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GPS Boat Comp For all the boaties out there, this one could literally be a life saver! You’ll never be lost again: as well as telling you exactly where you are at the moment, it will also show you your speed and heading and can even navigate you back to your starting point – or to that secret fishing spot! It can even tell you how much fuel you’re using, along with a host of other vital information. B ack in January of this year we described the GPS Car Computer, a project that used a low cost GPS module to provide a variety of data for the motorist. The project essentially consisted of a microcontroller, a display and a GPS module and it was obvious from the outset that it could be used for other applications. One reader, Nigel Hall of Dee Why in Sydney (himself an avid boatie!), was quick with the suggestion that we should make a nautical version. Nigel then went on to put in a lot of his time into defining a typical set of boating requirements and testing the final product. So here is the result – the GPS Boat Computer, a small electronic device intended to provide the weekend boater with a host of useful information. It will show your speed in knots, your heading, fuel consumption rate and the total amount of fuel consumed. It will also show your latitude and longitude and a compass needle pointing north. Possibly the most handy feature is the ability of the GPS Boat Computer to memorise up to eight of your favourite fishing or diving spots and later guide you back to the exact same 78  Silicon Chip spot – even if it is in the middle of the ocean. The hardware This project illustrates a trend in modern electronics… the use of intelligent and general function devices that can be reprogrammed to suit a variety of purposes. An extreme example of this are the Mars rovers Spirit and Opportunity. They have been reprogrammed many times to cope with the various conditions and terrain that they have met during their exploration of the red planet. In a similar vein the GPS Boat Computer uses virtually the same hardware and circuitry as the GPS Car Computer described in January and February 2010. The major difference is in the firmware which completely changes the character of the device. You do not need a PIC programmer for this change in personality; the new firmware can be loaded via USB from your computer and the Car Computer will become the GPS Boat Computer. You could, if you wished, then load the Car Computer firmware (also via by Geoff Graham USB) and flip back to that personality. In fact, you could drive to the marina with your GPS Car Computer, load the new firmware (it only takes 20 seconds) and sail off with your GPS Boat Computer! This also means that if you want to build this project from a kit you can simply buy and build the kit of parts for the GPS Car Computer (from Altronics) and upload the new firmware to turn it into a GPS Boat Computer. The only thing that you might need to do is consider a different enclosure – and we will talk about that shortly. Using the GPS Boat Computer The GPS Boat Computer is quite easy to use. You have a number of screens that show useful information which you select by pressing the UP or DOWN buttons. These buttons will wrap around the available set of screens when you have reached the end. When you turn the GPS Boat Computer off it will remember the last screen and will automatically return to that when power is reapplied. All screens have something that can be configured or changed. For example, when the clock screen is showing you can set the time zone. To change a setting you press the SET button siliconchip.com.au puter The GPS Boat Computer in action on the water, in its spray proof housing designed by Nigel Hall. It is showing the speed (in knots), a compass needle pointing in the direction of north and the boat’s current bearing (159°). (courtesy Nigel Hall) and then use the UP/DOWN buttons to adjust the value. Pressing the SET button a second time will save the value and either take you to another option or return to the main display. Options Some options are in the form of a question. The screen above shows a typical example of this and when presented with this you select YES or NO by pressing the UP/DOWN buttons then press the SET button to confirm the selection. Speed, compass and heading When you start up the GPS Boat Computer for the very first time the screen that you will see is shown above. This displays your speed in knots, a compass needle pointing north and your heading in degrees. The speed is averaged over a few seconds and is reasonably accurate, even down to one or two knots. The compass and heading are both derived from the change in latitude and longitude as your boat moves through the water. So if the boat is stasiliconchip.com.au tionary, both of these will be blanked to prevent them showing random and incorrect values. Pressing SET will enable you to switch the display to reverse video (green lettering on a black background). This might help in situations of poor visibility caused by bright sunlight. Fuel consumption Pressing the DOWN button will take you to the next screen. This shows your current rate of fuel consumption and the total fuel consumed. This data is dependent on the installation of the optional fuel flow sensor (described later). The instantaneous reading (litres/ hour or gallons/hour) can be used to adjust the speed of the engine for an optimal cruising efficiency. To reduce jitter in the display the reading is averaged over several seconds. The total fuel consumption can be used to estimate the amount of fuel remaining in your tank. You would normally reset the total to zero when you fill the tank and this can be done by pressing the SET button and using the UP/DOWN buttons to select YES at the prompt. By pressing SET you can also calibrate the amount of fuel consumed. The way to do this is quite straightforward. Fill the tank, zero the total and take your boat for a run. When you return, refill the tank to the same level and use the calibration screen and the UP/DOWN buttons to set the actual amount of fuel consumed. If you enter the amount consumed in litres then all readings will be in litres, similarly if you use gallons then all readings will be in gallons. Engine run time The next screen is the engine run time shown above. This is mostly used to determine when engine maintenance is due. It is assumed that when +12V is present on pin 2 of the 6 pin connector that the engine is running, so this pin would normally be connected to the ignition circuit of the engine. Point Of Interest (POI) This powerful feature will memorise your October 2010  79 current location and later guide you back to within a few metres of the same spot. This is great for returning to your favourite fishing spot, dive location etc. To set a POI to the current location you simply press SET when on a POI screen then select YES when prompted. The POI screen illustrated will show your distance to the location while the needle and number will show the bearing that you should take. To return to a location you just follow the needle and watch the distance count down. As you get closer the distance display will switch to metres with a resolution of one metre. Because the Earth’s surface is spherical, accurate calculation of the heading and distance would require the use of spherical trigonometry and 64 bit floating point numbers… something that is just not possible for our overloaded microcontroller. So we cheated and pretended that the earth was flat and used simple trigonometry and Pythagoras’ Theorem instead. The result is that from a distance the heading/distance will be a little inaccurate but, as you get closer, the accuracy will improve considerably. Depending on the signal level and other factors the GPS Boat Computer will direct you to within a few metres of the exact location – and that is pretty good when you are looking for a spot in the middle of the ocean. The GPS Boat Computer will memorise up to eight points of interest and these are shown in sequence when you press the UP or DOWN buttons. To reduce the number of screens that you have to step through, only the first three are shown by default. However, it is easy to enable the other POI screens using the Hide/Show function (see below for a description of this function). You can also use points of interest as waypoints. To do this simply set them in sequence (ie, POI #1, POI #2, etc). When you reach one of them pressing the DOWN button will show you the next. This way it would be easy to run from one waypoint to the next. By pressing SET and selecting the appropriate option you can also clear a POI and that screen will not show any directional data when you step through it with the UP/DOWN buttons. One facility that would have been really handy would have been the ability to manually enter the coordinates of a POI. Unfortunately the microcontroller just did not have enough program space for this function, so we reluctantly had to leave it out. Coordinates The latitude and longitude screen displays your current location in degrees, minutes and fraction of a minute. This information (and much more) can also be sent to your laptop via USB for use by navigation and mapping software. Signal level The signal level screen shows how many satellites should be in the sky (the number in the top left) and the number that are currently being used by the GPS module (bottom left). The bar graph shows the signal level of every satellite that can be detected but the module may not use every one if some of the levels are too low. When you are on the signal level screen you can adjust the backlight The EM-408 GPS receiver module used in this project (and of course in the GPS car computer from last January). It is available as part of the kit from Altronics (as mentioned earlier, the GPS Car Computer can become the GPS Boat Computer), as a separate item from Altronics or from a number of sources on the internet. Other modules might work; we know this one does! 80  Silicon Chip brightness for day and night conditions by pressing the SET button. Clock The last screen displays the current time in 12 hour (AM/PM) format with the seconds shown on the bottom right. The time is derived from the GPS signal and is accurate to within 100ms. Pressing the Set button will allow adjustment of the time in steps of half an hour (ie, this sets the time zone – the exact time is always derived from the GPS satellites). Special Functions The GPS Boat Computer has a couple of special functions that make it easier to handle the various screens that can be displayed. The first function is Auto Scan mode where the display will automatically flip from one screen to the next every three seconds. When it reaches the end it will wrap around and continue on from the top. When your hands are full this is far easier than pressing the UP or DOWN buttons to show a new screen. To enter Auto Scan mode you should simultaneously press both the UP and DOWN buttons. To exit this mode press any single button. You may not want to see all the screens as you cycle through them so you can configure the unit to hide some of them. To set this up you must hold down the UP button when you apply power. This will put the unit into a mode where you can set the following characteristics for each screen: • Show. • Hide in auto scan. • Always hide. When set to “Always hide” that screen will be skipped as if it did not exist. The “Hide in auto scan” setting is useful if you want to hide some screens during the Auto Scan mode but still have them available when you manually step through the screens. A good example is the Engine Running Time screen which you do not need to see while in Auto Scan. While configuring the Show/Hide function the SET button will step you through the three settings described above and the UP and DOWN buttons will move you through the list of screens available for configuration. To exit this mode you simply resiliconchip.com.au move and reapply the power. Measuring Fuel Flow One of the features of the GPS Boat Computer is its ability to measure the amount of fuel consumed by the engine in litres or gallons per hour and as a total. This function is optional so you can ignore this section if you wish to. There are two choices when it comes to measuring fuel consumption. If your engine is diesel or fuel-injected you can measure the length of time that the fuel injectors are open. This is the same technique as used in the GPS Car Computer and only requires a connection to the fuel injector solenoid. The voltage on the solenoid lead is normally high and it is pulled low by the engine management unit to open the solenoid and inject fuel into the cylinder. Normally the pressure in the fuel line is reasonably constant and therefore the time that the solenoid is open directly corresponds to the amount of fuel consumed. If you have a carburetted engine then the alternative is to use a paddle wheel flow sensor. These have a miniature paddle wheel or small turbine which is rotated by the flow, magnets attached to the rotating shaft will then cause a reed switch or a Hall Effect sensor to switch on as the magnet swings past. As a result we get a series of pulses at the output, the faster the pulse rate, the faster the flow. Paddle wheel flow sensors are easy to find but it is much harder to find one that is suitable for use with fuel. This is because the O-rings in a normal flow sensor will perish in contact with fuel and will eventually leak – which is a very dangerous situation in any boat. So, if you decide to use a flow sensor, check the specifications and only use one that specifically states that it is suitable for use with petrol or diesel fuel. Also be aware that some O-rings may be specified as OK with ordinary (unleaded) petrol but may not be so with petrol with ethanol additives. We bought ours via eBay but this particular product has since disappeared from their listings. RS Components (australia.rs–online.com) have a suitable but expensive sensor (part no. 508-2704). A similar sensor is branded MGL Avionics and is available from www. lightflying.com.au or oregonlightsport.com and other online suppliers. It is intended for experimental aircraft siliconchip.com.au The paddle wheel fuel flow sensor that we purchased on eBay. It has three connecting wires – one for ground, one for +12V power and one for the signal output. The output is open collector so we soldered a 3.3kΩ resistor between the signal lead and +12V. This could be squeezed inside the 6-pin plug if there is enough space. (Courtesy Nigel Hall) but is also suitable for our application. The GPS Boat Computer itself can be calibrated over a wide range so it should work with almost any flow sensor that has a pulse output. You might also find a number of paddle wheel sensors designed for marine applications that provide a NMEA 2000 output in place of the simple pulse output. NMEA 2000 is a complex marine communications protocol and regrettably beyond the capabilities of the microcontroller in the GPS Boat Computer. Two different versions of the firmware are available from the SILICON CHIP website, one for flow sensor measurement and the other for fuel injector measurement. The file names are: • GPS Boat Computer V1.0A Update. hex – will use the paddle wheel flow sensor. • GPS Boat Computer V1.0B Update. hex – will use the fuel injector monitoring method. Both are easily loaded via USB from your computer and you can experiment by switching between them if you wish. If you do not want to use the fuel consumption feature you can load either version of the firmware and ignore the fuel consumption screen or hide it by using the Show/Hide function described earlier. USB Interface The GPS Boat Computer is equipped with a USB interface that can be used with a laptop computer for displaying your location on electronic maps, recording you track and similar tasks. Essentially, when the microcontroller receives some data from the GPS module, it will also send a copy to your laptop using a virtual serial connection over USB. You can see the data stream by using a serial emulator such as PuTTY or HyperTerminal but a better application is to use software such as BSGPS or The fuel flow sensor mounted in the fuel line of a Chrysler outboard as recommended by the manufacturer, ie, vertically between the fuel pump and the carburettor. (Courtesy Nigel Hall) October 2010  81 OziExplorer to display your position on an electronic map (use Google to search for any of these names). This type of software can use scanned copies of your charts and pinpoint your position on them. If you search on the Internet you will find a wealth of other software that will allow you to navigate, log your movements, play with the GPS Module and much more. You can also check www. maps-gps-info.com/fgpfw.html where almost 500 free GPS-related programs are listed. To use this feature you need to install the Silicon Chip USB Serial Port Driver on your laptop (available from the SILICON CHIP website). This will work with all modern versions of Windows and full instructions are included with the driver, so installation should be easy. The GPS Boat Computer will be listed on your laptop in the Device Manager under Ports (COM and LPT) as “Communications Port – Silicon Chip USB Serial Port” with a specific COM port number. When you configD1 1N5819 REG2 LP2950CZ-3.3 OUT +5.3V IN GND 10 F 16V 11 +5.3V 4 Vdd CVref K 100k 32 Vdd MCLR 1 2 RA0 +1.35V +3.3V 4 Tx 3 Rx 2 GND 25 3.3k RC1 RA3 Tx 6.8k RE0 RC0 RB1 RB2 6 CON2 1 4 26 23 2 24 3 18 USB TYPE B RD0 C1out RD1 Rx RD2 D– RD3 D+ RD4 Vusb RD5 RD6 220nF RD7 SET 36 S1 UP DOWN S2 37 38 S3 13 X1 20MHz 22pF 22pF 14 7 8 6 15 5 3 4 RA1 IC1 PIC18F4550 33 -I/P RB0 +5.3V JP1 16 RC2 RB3 RA5 RB4 RB6 RB5 RE1 OSC1 RE2 RB7 OSC2 Vss 12 Vdd CLK CS2 CS1 A0 +12V IN A 19 2 5 1 EN 10 100 F 16V OUT 470nF D2 1N4004 K 10k EM-408 GPS MODULE +5.6V GND 2x 100nF 22k REG1 LM2940CT-5 A 220nF 5 V+ ure software on your computer you will need to specify this number to establish communications with the GPS Boat Computer. If the software also needs to know the communications parameters you can specify 9600 baud with one stop bit and no parity. When using USB you should make sure that there is not a jumper on the pins marked JP1. This jumper is intended for when you want to only power the GPS Boat Computer via a USB cable connected to your laptop. However, in most cases the GPS Boat LED+ Vcon LCD CONT 3 SG12232A LCD MODULE RES E R/W 18 8 9 LED– D7 D6 D5 D4 D3 D2 D1 D0 GND 17 16 15 14 13 12 11 10 1 VR1 10k CON1 100nF 6-PIN MINI DIN 20 6 5 3 4 2 34 1 35 19 20 21 82k* 22 27 28 29 30 3.3k 17 C B Q1 BC338 E 7 82k 39 (FUEL FLOW SENSOR INPUT) 9 +5.3V 82k 10 (ENGINE RUNTIME INPUT) 8.2k* (NAVIGATION LIGHTS INPUT) 40 47k Vss 31 47k LDR1*  * SEE TEXT 1 2 3 4 5 PC BOARD EM-408 CONNECTIONS SC 2010 GPS BOAT COMPUTER 1N5819 1N4004 A A K LM2940, LP2950 BC338 K GND B E C IN GND OUT Fig 1. The full schematic for the GPS Boat Computer. It is dominated by the microcontroller which is mostly concerned with receiving data from the GPS module and driving the LCD. The other items of note are the GPS module and the two voltage regulators which provide 5.3V and 3.3V. 82  Silicon Chip siliconchip.com.au Why every boatie needs one of these: a true story! The USB interface connects to CON2 on the PC board. Normally a boardmounting socket fits here but it this case we need it to be waterproof so it’s off the board. (Courtesy Nigel Hall). Computer will be permanently connected to the boat’s battery and so you should not install the jumper. Doing this would cause 5.3V to appear on the USB connector and possibly damage your laptop. Circuit Details Fig 1 shows the circuit diagram for the GPS Boat Computer. It is identical to the GPS Car Computer with the addition of a couple of resistors (in spare locations on the PC board) and so it uses the same PC board and components. The circuit is dominated by the PIC18F4550 microcontroller, a modern eight bit device manufactured by Microchip. This has a number of features that are important to us. Firstly it has plenty of input/output pins as we need them to drive the graphics LCD module. This module uses eight signal lines for data and another 7 control lines, making for a total of 15 pins that the micro needs to manage the display. The LCD module is a graphical device which means that we can turn off and on any pixel in its 122 by 32 pixels array. We use this capability to show a variety of fonts ranging from large digits for good readability, to small letters when space is restricted. We also display some graphic symbols like a compass pointer. The microcontroller also has full USB functionality built in and we can simply connect the USB signal lines direct to the chip. As described before, this allows us to send GPS data to a laptop which can then use additional software and maps to track our position. The GPS module sends and receives data to/from the microcontroller using a standard 4800 baud, 8-bit serial protocol with voltage levels of about 2.7V for a logic high and zero for a logic low. The 18F4550 microcontroller needs a voltage higher than 2.7V to reliably detect a logical high. So we first feed the data from the GPS module through an analog comparator (in the 18F4550) to obtain voltage levels that can be used by the micro. The GPS Car Computer article in January 2010 provides more detail of how this works. Sending data to the GPS module is a little simpler. The 3.3kΩ and 6.8kΩ resistors form a voltage divider to drop the 5V transmit data signal from the microcontroller to a level compatible with the GPS module which runs at 3.3V. The three front panel push buttons are connected directly to pins 36, 37 and 38 of the microcontroller. Internal pullup resistors are used to hold the inputs at 5V and therefore siliconchip.com.au Purely by co-incidence, as this feature was being prepared for publication one of the SILICON CHIP staff members, who owns a boat, was talking to a young acquaintance about boating in general. The young man admitted that he had owned a boat previously but had sold it after getting the fright of his life, swearing off boating for good! It transpired that he and some mates had taken the boat out fishing one moonless night on Pittwater, north of Sydney. For those who don’t know the area, it is a long, wide and relatively unpopulated waterway off Broken Bay, which itself is the very deep estuary leading to the mouth of the Hawkesbury River. They’d been fishing for quite a while and in the early hours of the morning it dawned on them that they didn’t have a clue where they were. They could have been anywhere between the southern end of Pittwater and some 20km away in the Hawkesbury itself. They didn’t know whether the lights they could see (kilometres away) were the suburbs on the eastern side of Pittwater, those on the northern side of Broken Bay or, indeed, the towns on the Hawkesbury. After driving around for some time trying (they didn’t know how long) to get their bearings in the pitch black, running low on fuel, they also didn’t know if they were headed upstream, back towards their launch site, or even straight out to sea (next stop, South America!) Compass? What was that? With no light and little or no swell to listen to, they didn’t know if they were close to any shore (almost all rocky) or thousands of metres from land. They were, quite literally, panicking – and as any authority will tell you, panic can kill! Fortunately, they eventually spotted the lights of a larger boat at anchor and managed to wake the (rather unhappy!) skipper to ask for help. The story had a happy ending – with directions, they managed to find the boat ramp around dawn – but it did prompt the very relieved owner to get rid of his boat! Now, just think of how much easier their lives would have been if they had one of these GPS Boat Computers on board: not only would it tell them where they were, it would also navigate them back to their launching ramp and/or any other “way points” they entered. And if they had happened to find that elusive, productive fishing spot (which they didn’t!) next time they went out (which they didn’t!), they could have navigated straight to it (which, of course, they didn’t!). We believe that a device such as this should be mandatory in every small craft – just in case. We believe that it’s as essential as life jackets and flares. Larger boats, especially more recent ones, tend to have GPS navigation and computing “built in” but small boats, by and large, do not. Even a hand-held GPS would be better than nothing but this device gives you extra features that the hand-held units do not. As our story shows, you don’t have to head offshore to get yourself into trouble. October 2010  83 * 10 F 10k X1 20MHz REG2 IC1 PIC18F4550 CON4 3.3k 100nF S2 100nF VR1 6.8k 10k S3 (TO LCD MODULE) 82k 100 F LP2950 Q1 BC338 47k 1 10 3.3k 22k 82k 47k CON3 CON1 Navigation Lights (pin1) 0V [Ground] (pin3) Fuel Injector/Sensor (pin5) R2 * S1 470nF R1 * LDR 100k CON2 CON5 1 REG1 LM2940 D1 5819 ^ D2 1N4004 1 PIEZO BUZZER 220nF 100nF 4 JP1 TO GPS MODULE 22pF 2 220nF 3 22pF ^ PIEZO BUZZER NOT REQUIRED IN GPS BOAT COMPUTER VERSION DOUBLE-SIDED BOARD - TOP LAYER ONLY SHOWN Fig.2: the PC board component overlay, D- (white) along with the D+ (green) connections for 0V [ground] (black) CON1 and CON2. +5V(red) shield The options for LDR or Nav Light control (R1/R2/ LDR) are shown Unused (pin6) in the table +12V Power (pin4) Engine Running (pin2) below. 1 LDR Navigation Light *LDR Install LDR 47kΩ resistor *R1 8.2kΩ resistor Leave Empty *R2 Leave Empty 82kΩ resistor The completed PC board. This prototype differs slightly from the final board, particularly around IC3 (REG2) and also the CON1 and CON2 connectors are shown here on the PC board. The board is compact but all components fit in with plenty of space. when a button is pushed the microcontroller will detect this as an input dropping to 0V. The remaining connections to the microcontroller are standard. The 220nF capacitor on pin 18 provides smoothing for the micro’s internal 3.3V supply. A 20MHz crystal connected to pins 13 and 14 provide the main clock for the chip. Finally, the transistor Q1 connected to pin 17 is used to control the brightness of the LCD backlight by pulse width modulation (PWM). The GPS Car Computer included a piezo buzzer for the over speed alarm but this is not used by the GPS Boat Computer firmware. We left it out of the circuit diagram and you do not need to install it if your device will always be operating as a GPS Boat Computer. External Connections All external connections are made through a 6 pin connector, CON1. 0V and 12V are on pins 3 and 4 of the connector and three other pins are used to monitor events in the boat. Pin 5 is used for the fuel injector solenoid or paddle wheel flow sensor input. Pin 1 is used to detect when the boat’s navigation lights are on (required if the LDR is not used) and Pin 2 is used to detect when the engine is running. All of these inputs use a voltage divider formed by 82kΩ and 47kΩ resistors to drop the input voltage to a level that is compatible with the microcontroller. If you are building the GPS Boat Computer from a GPS Car Computer kit then the only additional components that you need are an 82kΩ resistor at R4 and a 47kΩ resistor at R5, both for the Engine Running Time input. R3 and R6 are left vacant (as in the Car Computer) as the associated input is also not used in the GPS Boat Computer. Note that when using the boat’s navigation lights for A close up of the circuitry before being mounted in its sprayproof case. Again, this shows CON1 and CON2 as being PC board mounting. 84  Silicon Chip siliconchip.com.au control a 47kΩ resistor is installed vertically in the position marked for the LDR and pin 1 on CON1 must be wired to the circuit powering the boat’s lights. The microcontroller determines if it is day or night by monitoring the voltage at pin 40. A high voltage means that it is night and low means day. By using the following table when you assemble the PC board you can tell the Boat Computer that it is day or night via a light dependent resistor (LDR) or the boat’s navigation lights. Construction All the components are mounted on a single PC board which makes construction relatively easy. Fig.2 shows the component overlay – follow this diagram rather than that on any PC board, as some early PC boards had an incorrect screen print overlay. The PC board is double-sided and uses plated-through holes so you need to take a little care with soldering. Use a temperature-controlled soldering iron and only hold the iron on a joint for a few seconds. With plated-through holes it is difficult to remove a component so be careful that you have selected the right component with the correct orientation before you apply the iron. Start with the low profile components such as resistors and work your way up to the taller components such as the capacitors and transistor. Note that resistors R3 and R6 are marked on the PC board but not installed as they are reserved for future expansion. Don’t install the microcontroller or the GPS and LCD modules just yet, as you need to check the power supply voltages first. Be careful with D1 and D2 as they look alike. The same applies to Q1 (the transistor) and IC3 (the regulator), both are in TO-92 packages and can easily be confused. When soldering in the crystal (X1) ensure that it sits a millimetre or two above the PCB so that there is no danger of the metal case shorting the connecting pads underneath. The LM2940 regulator (IC2) sits on top of a small heatsink. Use a small amount of thermal grease between the regulator and the heatsink to ensure that the heatsink can do its job. Before screwing down the regulator check that the heatsink does not touch the solder pads on either side of the heatsink. The spacing is very close here but the heatsink can be moved around to ensure that it has adequate clearance. Once this is correct you can tighten the screw and nut. Finally solder the regulator’s leads – this is left to last so that the solder joint is not stressed. The PC board has provision for an extra connector (CON3) which also can be seen in photographs of the prototype. Ignore this, as it is intended for use with a device like the 5.3V siliconchip.com.au 100nFF 100n 22pFF 22p 22pFF 22p TO GP GPS S MO MODU DULE LE CON5 CO N5 1 10 F 10k X1 20MHz IC1 IC 1 PIC PIC18F 18F4550 4550 3.3k 3. 3k 100nFF 100n REG2 RE G2 LP2950 LP 2950 D2 1N 1N4004 4004 220nFF 220n Fig 3. Before you plug in the microcontroller and connect the GPS module you should check that these voltages are present. Both have a tolerance of ±150mV. If you cannot measure the correct voltages you should check D1, D2, IC2, IC3 and the power connection. 3.3V Parts List – GPS Boat Computer. 1 PC board, code 05101101, 140mm x 57mm 1 GlobalSat Technology EM-408 GPS module – available from Altronics (K1131) or via the ’net. 1 SG12232A 122 x 32 dot matrix LCD (Altronics Z7052) 1 20MHz low profile crystal (X1) 1 high output sealed mini buzzer, PCB mounting (Altronics S6105) 1 2-pin header 1 20-pin header 1 20-way single row header socket (8mm high socket base) 1 micro U-style heatsink for TO-220 (19x19x9.5mm) Semiconductors 1 PIC18F4550-I/P microcontroller (IC1) (available from www.futurlec.com) 1 LM2940CT-5 or LM2938ET-5.0 5.0V voltage regulator – TO-220 package (IC2) 1 LP2950CZ-3.0 voltage regulator TO-92 Package 3.3V (IC3) 1 BC338 transistor (Q1) 1 1N4148 diode (D1) 1 1N5819 Schottky diode (D2) Capacitors 1 100µF 16V electrolytic (105°C rating) 1 10µF 16V tantalum 1 470nF MKT 2 220nF MKT 3 100nF monolithic 2 22pF ceramic Resistors (0.25W 5%) 1 10Ω 2 3.3kΩ 1 6.8kΩ 1 8.2kΩ 1 10kΩ 1 22kΩ 3 47kΩ 3 82kΩ 1 100kΩ 1 10kΩ trimpot (vertical mount, front adjust) 1 LDR (light dependent resistor) 10kΩ to 1MΩ (Altronics Z1621) (optional – see text) Parts List for the Sealed Case 1 UB3 box [Jaycar HB6013 (black) or HB6023 (grey)] 1 IP67 waterproof USB “type B” female chassis connector, (Altronics P9725) 1 USB sealing cap (Altronics P9840) [for when the USB connector is not in use] 1 IP67 6-pin locking chassis mount male connector (Altronics P9366) 1 IP67 6-pin locking female line connector (Altronics P9356) 3 SPST momentary pushbutton switches, black solder tail (Altronics S1084 or Jaycar SP-0700) 6 PC Pin Sockets (Jaycar HP1260) 1 3mm thick Perspex or acrylic sheet, 3mm – cut to size for UB3 box (Jaycar HM-9509) 4 12mm M3 tapped spacer** 4 10mm M3 untapped spacer** 4 20mm M3 screw** 4 6mm M3 screw** 1 10mm M3 screw**    ** preferably nylon or 9 M3 star washer**     marine-grade 4 M3 flat washer** stainless steel 1 M3 nut** 100nFF 100n 6.8k 6. 8k 10k October 2010  85 Microchip PICkit 3 during software development. With the case design shown there is plenty of space between the main board and the LCD module so you can use an IC socket for IC1, which makes fault-finding and testing much easier. When handling the microcontroller and LCD you should take the standard precautions against electrostatic discharge which could zap these devices. This means making sure that your work surface, your soldering iron and you, are all grounded. The LCD is not installed yet but its connectors can be. It plugs into a 20-pin connector on the main board via a single row 20-pin header strip. Start by inserting the long pins of the 20-way pin header strip through the matching holes on the LCD from the bottom. The plastic spacer should be flush on the underside of the display’s PCB and the shorter pins underneath. Solder and trim the pins on the top of the board while ensuring that the spacer underneath remains flush with the board. Then remove the plastic spacer leaving just the pins. This is best done with a fine screwdriver – lever down one end of the spacer by a few millimetres, then the other end followed by the middle. After repeating this a few times the plastic spacer will slide off the pins. The GPS module is supplied with a cable with identical connectors on each end. Cut off one of the connectors, bare the wires and solder to the pads marked CON5. The grey wire goes to pad 1 which is marked accordingly (the left hand pad when viewing the board with the silk screen printing the right way up). The other wires should be soldered in the same sequence as they emerge from the connector. then need to load the GPS Boat Computer firmware from your computer using the USB interface. Testing The firmware for the microcontroller is loaded in a two step process as illustrated in Fig 4. First the full copy of the GPS Car Computer firmware version 1.1 needs to be programmed into a blank microcontroller using a PIC programmer. A copy of this firmware can be found on the SILICON CHIP website under Downloads for January 2010. You only need to do this once and from then on new firmware will always be loaded via the USB interface. If you built your device from a kit of parts then the supplier should have already programmed the chip for you – so you can skip this and move onto the next step. As Fig.4 shows this firmware contains a bootloader. This is a small portion of software, 2KB in size, which sits in the bottom of memory and watches to see if the SET button is held down while power is applied. The best way to load this software is to disconnect the GPS Boat Computer from a power source (eg, unplug CON1), place a jumper on JP1, and connect the GPS Boat Computer to your computer (via a USB cable plugged into CON2) while holding down the SET button. Placing the jumper on JP1 means that the GPS Boat Computer will be powered from the USB interface. When this condition is detected the bootloader will take control of the USB port and reconfigure it to pretend that As a final check, closely inspect the board with a high power magnifying glass. Carefully check every solder joint for blobs, shorts or poor joints. With all components in place (except the microcontroller, switches, GPS and LCD) you should make a quick test to ensure that the voltages are correct. With 12V power applied you should be able to measure about 5.3V between pins 11 and 12 of the microcontroller socket. Between pins 2 and 5 of the GPS connector (CON5) you should be a ble to measure 3.3V. Both could vary by plus or minus 150mV. Refer to Fig.3 for the measurement points. If you cannot measure the correct voltages you should check D1, D2, IC2, IC3 and the power connection. You can now insert the pre-programmed PIC18F4550 into its socket (again, follow the component overlay on P84, as some PC boards show this upside down!), then plug the LCD and GPS into the PC board. When you apply 12V power the LCD should immediately show the firmware version followed by a message indicating that it is searching for satellites. You may need to adjust the 10kΩ trimpot to get an image on the display and then continue adjusting it for a good contrast. The device will start-up as a GPS Car Computer as that is the initial firmware loaded in the chip by the kit supplier. As explained in the next section, you GPS CAR COMPUTER GPS BOAT COMPUTER BOOT LOADER BOOT LOADER Fig.4a: a “factory fresh” or blank microcontroller must first be programmed using a PIC programmer such as the PICkit3. This will load two components, a bootloader, which is responsible for future program updates and the GPS Car Computer firmware. If your microcontroller came in a kit then the kit supplier should have already programmed the microcontroller and you can skip this step. 86  Silicon Chip Loading the firmware Fig.4b: to load the GPS Boat Computer firmware, you should hold down the SET button while applying power. The bootloader will take control and establish communications with your computer over the USB interface, allowing you to upload new firmware via USB – no programmer is required. Using this method you can also load other updates or revert to the GPS Car Computer firmware. siliconchip.com.au Fig.5: while the electronics is basically the same, there are some layout differences between this diagram and the GPS Car Computer from last January – mostly to do with ensuring moist air or even the occasional greenie doesn’t play havoc with the works! THIN BEAD OF NEUTRAL CURE SILICONE SEALANT FRONT PANEL PUSHBUTTON SWITCHES FRONT PANEL MOUNTING SCREWS CLEAR FRONT PANEL (RECESSED INSIDE THE UB3 BOX) LCD MODULE LCD MODULE PC BOARD 12mm LONG UNTAPPED SPACERS 20-WAY SIL SOCKET 10mm M3 TAPPED SPACERS MAIN PC BOARD BACK OF UB3 BOX IP67 RATED USB CONNECTOR (CON2) it is a Microchip PICDEM FS evaluation board. Your computer will recognise this new device and prompt you to load the appropriate device driver (included in the software package). To upload the GPS Boat Computer firmware you need to run software that knows how to reprogram the PICDEM FS board (which is what the microcontroller is pretending to be). As shown in Fig.4 this software will overwrite the upper portion of the firmware while still leaving the bootloader (that is stored in lower memory) in control. When you subsequently remove and reapply the power (without holding down any buttons) the micro will run the firmware in the upper portion of memory and your gadget will have changed to a GPS Boat Computer. While this process might sound complex reprogramming only takes 20 seconds and all the necessary software and instructions are included in the software package on the SILICON CHIP website. The software package also includes a USB-loadable version of the GPS Car Computer firmware so that you can go back to that if you need to. However, you should note that all settings will be lost if you do this. Troubleshooting With only a few active components in this project it should be easy to track down any faults. Firstly, check the two supply voltages as described earlier, as nothing much will happen if they are not correct. Next, check the microcontroller. This is best done by carefully measuring the voltage between pin 4 and pin 12, which should be between siliconchip.com.au 20mm M3 SCREWS WITH STAR LOCKWASHERS 6-PIN MINIATURE IP67 LOCK DOWN CONNECTOR (CON1) 1.2V and 1.5V. This voltage is created by the internal voltage reference and implies that the firmware is running and that the microcontroller is OK. In the absence of this voltage, check pins 13 and 14 with a ’scope for a 20MHz sine wave, indicating that the main clock is present. Next is the LCD. First check the voltage on pin 3 of the LCD (VCON) – it should be under 0.5V. This voltage is controlled by the 10kΩ trimpot (contrast) and if not correctly adjusted the display will appear blank. The microcontroller only sends data to the LCD and does not expect any response. So, even with the LCD removed or faulty, you should still see signals on the data lines to the LCD. If the LCD is blank or showing rubbish the only things that you can do is check that it is plugged in correctly (watch for bent pins!) and that there are no solder bridges on the connector. With the microcontroller running and the LCD showing the startup message the only other fault would be with the GPS module. The microcontroller will display an error message if the module is not connected or running, 6mm M3 MACHINE SCREWS WITH STAR & FLAT WASHERS ALL SCREWS, NUTS, WASHERS ETC SHOULD BE MARINE GRADE STAINLESS STEEL so that type of fault should be obvious. Don’t worry if the GPS Boat Computer initially sits with the LCD showing a message saying “SEARCHING”. The GPS module normally keeps track of the available satellites in its internal memory, which is kept alive by a super capacitor. If this capacitor has lost its charge, the module will have to reload the tracking information from a satellite - and this can take up to 15 minutes. This only happens once, subsequently the GPS will use its memory of the data and start up in 45 seconds or less. If, after a long wait, the GPS module still cannot get a signal you should try moving the unit outside or near a window so that it can “see” the sky. While it is searching you can press the Set button to get the Signal Levels display – this will show you how many satellites can be seen and their signal levels. It is possible for the GPS module or the microcontroller lock up or crash. If this happens you can press and hold the DOWN button while plugging the GPS Boat Computer into power. This will cause the microcontroller to reset +12V GPS BOAT COMPUTER CON 1, PIN 5 +0V Fig.6: the connections we made to our flow sensor. The 3.3kΩ resistor is required to pull up the output voltage as the sensor used an open-collector output. Your sensor will probably be similar but check the documentation. October 2010  87 Resistor Colour Codes o o o o o o o o o No. Value 1 100kΩ 3 82kΩ 3 47kΩ 1 22kΩ 1 10kΩ 1 8.2kΩ 1 6.8kΩ 2 3.3kΩ 1 10Ω 4-Band Code (1%) brown black yellow brown grey red orange brown yellow violet orange brown red red orange brown brown black orange brown grey red red brown blue grey red brown orange orange red brown brown black black brown itself to the default settings and send a command to the GPS module also resetting it to its factory defaults. Spray Proof Enclosure The original GPS Car Computer was designed for use in a car and therefore no attempt was made to protect its internals from the elements. This is definitely not acceptable in a marine environment. We recommended a case that can be completely sealed so that the electronics are protected from corrosive salt air (it doesn’t even have to be salt spray). It’s not so much that the case needs to be waterproof to stop water getting in – if that situation occurs you’re in much more trouble than a GPS Boat Computer can assist with – but the moist air on a boat usually gets into everything and starts attacking any metal it can. Nigel Hall, who suggested the GPS Boat Computer, also developed an alternative case and we describe it here. Nigel’s design comprises a Jaycar UB3 “jiffy” box (130 x 67 x 43 mm) with a front panel fabricated from a sheet of clear Perspex or Acrylic. The push buttons are mounted on the front panel while the USB connector (CON2) and the 6 pin connector (CON1) are panel mounting components and are attached to the rear panel. These connectors are IP67 rated (immersion up to 1m) and have a rubber sealing washer which is best installed on the inside of the box. While the front panel push buttons are not rated at such a high standard they should be adequate. These switches and connectors replace the corresponding board mounted components used in the GPS Car Computer so they need to be wired to the solder pads for the original components. Fig.2 illustrates the wiring 88  Silicon Chip 5-Band Code (1%) brown black black orange brown grey red black red brown yellow violet black red brown red red black red brown brown black black red brown grey red black brown brown blue grey black brown brown orange orange black brown brown brown black black gold brown for the connectors (CON1 and CON2) and this should be implemented using lightweight hookup wire running from solder stakes on the PC board to the connectors. The front panel buttons also connect to the PC board with lightweight hookup wire The best way to do this is use short wires and PC pin sockets (Jaycar HP1260) to plug the leads onto pins soldered onto the main board. This will allow you to easily remove the front panel for testing without having to use long and unsightly wires which could be seen through the clear front panel. Assembly As Fig.5 shows, the completed assembly of main PC board and the LCD module are separated by spacers and mount using more spacers onto the bottom of the box. When putting everything together it is best to first attach the LCD module to the main board using the 20mm machine screws which run through the 12mm Capacitor Codes Value F value IEC Code EIA Code 470nF 0.47uF 470n 474 220nF 0.22uF 220n 224 100nF 0.1uF 100n 104 22pF – 22p 22 untapped spacers and fasten onto the 10mm tapped spacers. This assembly can then be easily lowered into the box and secured by the 6mm screws through the bottom of the box. To allow the GPS module to fit in its position you will need to trim some of the plastic ribs. You’ll also need to drill a hole in the rear so that the external antenna connector can poke though. This also helps to hold the module in position. Normally you will not need access to this connector so you can cover the hole with a square of adhesive tape to keep the elements out. Even better for waterproofing is a dob of neutral-cure silicone sealant – but you must be sure you’re never going to connect an external antenna! In the Jaycar UB3 box the top of the mounting pillars (which secure the front panel) sit about 3mm below the top edge of the box. This allows you to sit the front panel inside the edges of the box and, using some marinegrade stainless steel screws (not the ones supplied with the box!), securely fasten the front panel to the mounting pillars. This cannot be easily achieved with the Altronics version of the UB3 box, as their mounting pillars extend to the top of the box, preventing you from The rear of the prototype spray-proof case showing the mounting screws, weatherproof connectors and the hole drilled for the GPS module’s external antenna connector. This hole should be sealed when not in use. (courtesy Nigel Hall). siliconchip.com.au easily recessing the front panel. You could grind down these pillars to allow for recessing but achieving the same level on each pillar migh be difficult. For protection, immediately before screwing the front panel in place (and only after all testing and troubleshooting) a thin bead of silicone sealant can be run around the edge of the Perspex or Acrylic lid to properly seal it. As a final touch you could, if you wished to hide the electronics, attach a label (with a cutout for the LCD) on the inside surface of the clear front panel. Wherever possible, the screws, nuts, washers and spacers used should be marine-grade stainless steel (which you may have to source from a ships’ chandlery). Even with a sealed case standard hardware will corrode on a boat, often quite quickly. One unfortunate outcome of a sealed case is that it could get quite hot inside due to the heat generated by the LM2940 regulator (IC2). To reduce this, you could place an external 12Ω 5W resistor in series with the 12V supply (on pin 4 of CON1). This will reduce the supply voltage to the GPS Boat Computer by 3 volts and correspondingly reduce the heat generated by the regulator by up to 40%. Installation There are five connections that you need to make from the mini-DIN power and input connector (CON1) to your boat’s electrical system. These are illustrated in Fig.2 and consist of: • Pin 4, which is the main power (+12V) input to the GPS Boat Computer and should be connected to a power source that is powered on whenever you would want to use the GPS Boat Computer. This is not usually the engine ignition switch, as there are times when you want to know your position without the engine running (eg, drifting over a fishing ground).    As explained in the previous section, if you are using the sealed case design you should also install an external 15Ω 5W resistor in series with the +12V supply to reduce the heat generated inside the case. The supply must also be protected with a 500mA fuse either inline or via a fuse block. • Pin 3 is the ground (negative). • Pin 2 should connect to the engine ignition circuit and is used to determine the engine’s running time. siliconchip.com.au This input should be at +12V when the engine is running and zero volts when not. • Pin 1 is used to control the brightness of the display when an LDR is not used. It should be wired to the circuit for the boat’s navigation lights so that +12V is present on the line when the navigation lights are illuminated (ie, after sunset). • Pin 5 is the input for the fuel consumption measurement and should be connected to either the fuel injector solenoid or fuel flow sensor depending on the version of the firmware loaded. • Pin 6 is not connected. It is available for future development. If you are using the fuel injector sense method you will have to connect pin 5 on CON1 to the negative lead of one of the fuel injector solenoids, preferably near the engine management unit as that position should be more protected from salt spray and other environmental hazards. If you are using a paddle-wheel sensor you will probably need to connect it to the same source of power used by the GPS Boat Computer and install a pull-up resistor on the output line which connects to the GPS Boat Computer. Fig.6 shows the connections that we made to our sensor – yours will probably be similar. The reason for the resistor is that most paddle-wheel sensors have an open collector output where a transistor in the sensor will pull the output low and the resistor is needed to pull it high again when the transistor is turned off. Typically a 3.3kΩ resistor wired to the 12V supply will be sufficient but your sensor might already have the resistor built in, so check the documentation. You should also refer to the documentation for your device when determining how and where it should be mounted. Generally the manufacturer will recommend that it be mounted vertically between the fuel pump and the carburettor but before any pressure regulator. This is to minimise the formation of vapour pockets. So, that is the GPS Boat Computer. All that is left is to wish you “happy navigating” (and perhaps “great fishing!”). For up to date errata, notes and new firmware go to http://geoffg.net/ boatcomputer.html SC Helping to put you in Control Control Equipment Port Powered Isolated RS232 to RS485 Converter Optical isolation effectively protects this RS-232 to RS -485 converter from transient surges, ground loop, and lightning. TOD-008 $52.50+GST Capacitive Proximity Switches Available in M12, M18 and M30 diameter. They are 4 wire NO+NC and are available with NPN or PNP outputs. IBC-009 From $49.00+GST DIN Rail Springcage Terminals. So much faster to use than screw terminals. A screwdriver is used to open the terminal, allowing insertion of the wire. TRM-215 From $0.99+GST myPCLab Compact Data Acquisition tool connects to a PC via a USB port and monitors 2 universal analog inputs (Thermocouple, RTD, 4-20mA and volts). NOV-010 $129 +GST Split Core Current Transformer. Want to measure AC current consumption. This small current transformer outputs 020mA AC over 0-60A AC primary current. ALT-051 $29.95+GST Freetronics Ethernet Shield with POE. Let your Arduino controller do Twitter updates automatically, serve web pages, connect to web services, display sensor data online, and control devices using a web browser. FRA-002 $40.85+GST Ph: 03 9782 5882 New, Easier to Use Website www.oceancontrols.com.au October 2010  89