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Pt.3: By JOHN CLARKE Water Tank Level Meter: Telemetry Base Station Designed to team with up to 10 Water Tank Level Meters, this Base Station lets you monitor water levels from a remote location (eg, inside your home). As a bonus, it also includes an option for electric pump control. T HE ABILITY TO MONITOR water tank levels from a remote location can be very useful in certain circumstances. This particularly applies if you have several water tanks or if the tanks are hard to access, or you want to include automatic pump control. This Base Station is intended for use with the telemetry version of the Water Tank Level Meter described in the November & December 2007 issues of SILICON CHIP. It has an inbuilt 433MHz wireless receiver and can handle data transmissions from up to 10 level meters and display the results on a 2-line 32-character LCD module. In bargraph mode, it can show up to 10 tank levels simultaneously, while the 80  Silicon Chip digital readout mode shows individual tank levels to 1%. As shown, the Base Station is a compact unit that can be placed on a shelf or a desk or attached to a wall via integral mounting brackets. The display is backlit so that it can be readily seen under all lighting conditions. The only controls are four pushbutton switches situated in a line immediately below the LCD module. These are used to control the display format and to set up pump control. Power for the Base Station comes from a 9V DC 200mA plugpack. Display format As mentioned, the display can be switched to operate in one of two formats. The first format shows all enabled tanks and their levels as an 8-level bargraph on the one display (All Tanks View diagram). In this format, the top line shows the word “LEVEL” and the tank levels are displayed as a rectangular tank with sides. Each tank level is shown by the height of the bars in the tank and each bar corresponds to a 12% or 13% step in level. So, for example, with only the bottom bar showing, the level is above 12%. For two bars the level is above 25%, while four bars represent a level above 50%. If the tank is full (ie, at 100%), the tank symbol is just a full rectangular block (ie, all bars are on). Conversely, an empty tank or one that is below 12% in level shows an “e” for empty. The second line in the display shows the word “TANK” and the number of each tank is displayed directly beneath each of the tank level bargraphs. As mentioned last month, each Water Tank Level Meter is assigned a tank siliconchip.com.au number using a 0-9 BCD rotary switch. These selected numbers are the ones that are displayed for each tank. Note that only the tanks that are monitored with a Water Tank Level Meter need to be shown on the display. So if you only are monitoring Tank 1 for example, then that number is all that needs to be displayed. Basically, you can enable which tank numbers the display will show. If only five tanks are enabled and they utilise numbers from 1-5, then each consecutive number will be separated by a space. If there are more than five tanks or if numbers above five are used, then there is no space between each consecutive tank number on the display. In practice, the tanks are displayed from left to right in a 1-9 and then 0 sequence. However, if one or more of these tank numbers is not enabled, the display will include a space where the tank number would otherwise be positioned. View switch Pressing the View switch accesses the alternative digital display format (Individual Tank Detail diagram). In this mode, individual tank data is shown. For example, if tank 1 is selected, the first line will show: “TANK1” followed by “LEVEL” and then the water tank level value as a percentage. For example it may show “27%”. The levels can range from 0-110%. If no tanks are enabled in this mode, the display will show “TANK ERROR ENABLE A TANK!” (we describe how to do this a bit further on). The second line in this display format shows the temperature reading in °C and this can range from -99°C through to +99°C (this is the temperature inside the corresponding Water Tank Level Meter). Following this is the word “CELL” and then the cell voltage (eg, 1.21V). If the cell voltage is below 1.15V, then a small cross will be displayed just before the voltage value. This indicates that the cell in the level meter in not charging correctly which may soon prevent it from operating. Each enabled tank can be checked in sequence using the Up () or Down () switches to select the tank number required. Note that only enabled tanks will be displayed. For example, if you have enabled tank 1, tank 3 and tank 4, then the Up switch will cycle between siliconchip.com.au Data for the Telemetry Base Station is transmitted from one or more Water Tank Level Meters (up to 10), as described in the November & December 2007 issues of SILICON CHIP. 1, 3, 4, 1, 3, 4, etc. Similarly, the Down switch will cycle between these numbers in the reverse sequence. Note that if you have only enabled one tank, the Up and Down switches will have no effect. If the base station has not received any data from the selected Water Tank Level Meter it will show a question mark (?) in the space that normally shows tank level. In greater detail, this will be shown in place of the bargraph for the “All Tanks View” mode and in place of the the level and temperature value portions for the “Individual Tank Detail” format. In addition, a ‘?’ is initially displayed for level, temperature and cell voltage when the Base Station is switched on, before it receives data from the Water Tank Level Meter. The ‘?’ will reappear after data for that particular tank has not been received for more than an hour. However, the cell voltage will still be displayed and will show the last measured voltage before transmission was lost. Loss of reception for over an hour Typical Base Station Display Readings ➊ (1). The “All Tanks View” format gives a graphical view of all enabled tanks and their contents. ➋ (2). The alternative “Individual Tank Detail” format shows detailed data for each tank in digital format. ➌ (3). Pressing the Set switch brings up the tank options. This is the display if a tank is not enabled. ➍ (4). The unit can be programmed to separately control up to 10 pumps, turning then on or off at set levels. January 2008  81 Features & Specifications Features Monitors up to 10 Water Tank Level Meters Digital readout shows 1% level resolution for individual tanks Switchable bargraph level display for monitoring all tanks simultaneously Temperature and cell voltage monitoring for each tank meter Can automatically control up to 10 electric pumps Automatic pump-off switching with water level and temperature Water level threshold adjustment for pump off Temperature threshold adjustment for pump off Specifications Number of tanks monitored: 10 maximum Bargraph display: eight levels plus “e” for empty, corresponding to levels of 0, 12, 25, 37, 50, 62, 75, 87 & 99% Individual display: percentage display from 10-110% in 1% steps; temperature from -99°C to +99°C.; cell voltage with 2-digit 10mV resolution Pump Control: up to 10 pumps Temperature threshold: pump switches off for temperatures below the setting from -9°C to +99°C; adjustment can be made in 1°C steps. Level threshold: pump switches off for level settings below 50%. Alternatively, pump switches on for level settings above 50%. Adjustment is available in 1% steps from 0-100% Invalid data: displays shows a “?” if no valid data at power up and after one hour without fresh data. Power: 9-12V DC <at> 100mA Encode: 16 selections to help prevent reception of a neighbouring signal can mean that the Water Tank Level Meter has a low cell voltage and has ceased transmitting. The last measured cell voltage before data was lost can help solve the problem. Cell voltages at or below 1.10V reveal that the cell is discharged. Alternatively, the Water Tank Level Meter could have met with a much more catastrophic disaster! Enabling a tank As noted above, a tank must be enabled for the Base Station to display its data. To do this, you first press the Set switch so that the tank options are displayed. If a tank is not enabled, the display will show, for example, <TANK1>OUT on the top line. To select the required tank number, you press the Up () switch to successively select numbers 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, etc. That done, you enable the selected tank by pressing the Down () switch. This changes the display 82  Silicon Chip so that it now shows the PUMP ON or OFF indication and settings on the second line of the LCD. Once a tank has been enabled, you can continue to enable more tanks by pressing the Up switch to find the tank number and then the Down switch to enable the tank as required. That done, it’s just a matter of pressing the View switch to return to the main display format. Pump control Once a tank has been enabled, the menu for its pump control can be displayed by pressing the Set switch. The display then shows various options for controlling an electric pump associated with that tank. First, however, note that the pump number for a particular tank is the same as the tank number; ie, a pump associated with tank 1 is pump 1, a pump associated with tank 2 is pump 2 and so on. Initially, when a tank is first enabled, the pump is set to OFF. To turn the pump on, first press the Set switch to display <OFF> following the word PUMP. The setting is then changed from OFF to ON by pressing either the Up () or Down () switch When this is done, the pump switches on and the word “ON” will be displayed, provided the pump control threshold values are OK. The pump control threshold values are shown on the second line of the LCD. This line starts with “OFF <at>” (off at), followed by a level setting in percent (eg, 5%) and a temperature setting in °C (eg, -2°C). In practice, the pump will not switch on if the temperature is below the threshold value or if the water level is beyond the threshold value. Conversely, if a pump is on, it will switch off if the values received from the level meter are below the temperature threshold or beyond the water level threshold setting. The water level setting threshold works in two ways. First, suppose you are using a pump to extract water from a tank, as is normal if the tank is used to supply water for a house. In this case, the unit would be set to automatically switch off the pump when the tank water drops below the set threshold. This is done to prevent the pump running continuously when the tank water has been depleted. Basically, the unit will switch off the pump if the level threshold is set to 50% or less. Typically, the threshold would be set well below 50%, at say 15% or 10%. Conversely, you might want to use a pump to fill a tank from another supply; eg, from a bore or from another tank. In this case, you want the pump to switch off when the water level reaches the preset value so the tank does not overflow. For the Base Station pump control, a level setting that is over 50% will switch the pump off when the water level reaches the set threshold. So the pump automatically switches off for rising or falling levels, depending on whether the setting is above or below the 50% threshold. Note that the Base Station does not directly control the pump (or pumps). Instead, it transmits a UHF signal to a UHF Remote Control Mains Switch and this in turn switches the pump on or off. The UHF Remote Control Mains siliconchip.com.au Fig.1: the Base Station uses a 433MHz receiver module to pick up data from the Water Tank Level Meter(s). This data is then fed to PIC micro IC1 which in turn drives the LCD module. The 433MHz transmitter is only necessary for pump control. Switch will be described in SILICON CHIP next month and you will need to build one of these for each pump you wish to control. Temperature control If the outside temperature is at or below 0°C, the water in the pipes that connect to the tank may freeze. If that happens, then having a pump start up could destroy both the pump itself and the connecting hoses. For this reason, the unit includes temperature control. This automatically switches the pump off if the temperature drops below a preset value. siliconchip.com.au The actual threshold setting will depend on the climate at your location and how well the pipes are protected from the environment. If your pipes are underground, then they may never freeze up. Conversely, if the pipes are exposed, then they may easily freeze. Generally, you would set the temp­ erature to around -2° C. That’s because the water in the pipes is not likely to freeze until the temperature drops several degrees below zero for a reasonable period of time. Remote Control Mains Switch In operation, the UHF Remote Con- trol Mains Switches receive the on or off signals from the Base Station to control the pumps. These switches are each assigned a number from 0-9, corresponding to the tank number and its pump. This ensures that the correct UHF Remote Control Mains Switches respond to signals from the Base Station. Another important feature of each UHF Remote Control Mains Switch is brownout detection. A brownout occurs when the mains voltage drops well below its normal value, due to a fault condition in the mains supply. This not only affects the brightness of lights but more seriously, can cause January 2008  83 Fig.2: follow this parts layout diagram to build both the main board and the switch board. Take care with the orientations of the 433MHz receiver and transmitter modules – their pin assignments are clearly marked on their PC boards. Note also that switches S1-S4 must be installed with their flat sides as shown. This view shows the completed main-board assembly, prior to installation of the LCD and switch modules. Note the the PIC microcontroller is not normally plugged into its socket until after the initial power supply checks have been completed. pumps and other electric motors to burn out. That’s because, at low voltage, electric motors draw excessive current (and thus overheat) when they do not spin at their normal RPM. To prevent this, the UHF Remote Control Mains Switch switches off the supply to the pump if a brownout is detected (more on this next month). Circuit details The circuit for the Water Tank Level Meter Base Station is really quite sim84  Silicon Chip ple. As shown in Fig.1, it’s based on a PIC16F88 microcontroller (IC1) and a 2-line x 16 character LCD module. Apart from that, there’s just a couple of 433MHz receiver & transmitter modules, a BCD switch, four pushbutton switches and a few sundry bits that are mainly in the power supply. Of course, some of the components are quite complex in themselves, such as the 433MHz receiver and transmitter modules, the LCD module and the microcontroller. However, these can be considered simply as “building blocks”, since we don’t need to know too much about their internal operation to make them work as intended. IC1, the microcontroller, is at the heart of the circuit. It monitors the signal from the 433MHz receiver and in turn drives the LCD and the 433MHz transmitter that provides pump control. It also monitors pushbutton switches S1-S4 and the encode switch (S5). Note that while the 433MHz receiver is vital to receive data from the level meters, the 433MHz transmitter is only necessary for pump control. If you don’t intend to use this unit for pump control, then the transmitter can be omitted. As shown in Fig.1, the data received by the 433MHz Rx (receiver) module is applied to the RA5 input of IC1 via a 1kW current limiting resistor. This resistor is included because IC1 can latch up if excessive current flows into or out of this pin if the input goes above +5V or below 0V. In operation, IC1 reads the data signal by clocking it in at a rate set by the transmission locking pulse. This data is then accepted by IC1 if the format is correct and the encode value matches the setting of BCD switch S5 (ie, the encode switches in the level meters and the Base Station must match each other). If the encode settings do not match, then the data signal will be rejected. siliconchip.com.au S5 is connected to the RB4, RB5, RB6 and RB7 inputs of IC1 and can pull these inputs to ground when its ‘2’, ‘4’, ‘1’ & ‘8’ switches are closed respectively. Basically, it is a rotary switch with 16 settings ranging from 0-9 and A-F. For the 0 setting, all switches are open and for the F setting all switches are closed. Settings in between 0 and F have different combinations of open and closed switches. For example a ‘1’ position will tie IC1’s RB6 input to ground. Conversely, each RB4-RB7 input will be pulled to the +5V supply rail when its corresponding switch is open. That’s because each of these inputs has an internal pull-up resistor of about 20kW. In operation, each switch setting can be checked by IC1 because a low voltage on the input means that the switch is closed, while a high voltage means that the switch is open. Switches S1-S4 (View, Set, Down & Up) on the RB0-RB3 inputs are monitored in a similar way. Ports RA0-RA3 & RA6-RA7 are used to drive the LCD module. As shown, RA0-RA3 drive the D4-D7 data lines, while RA6 & RA7 drive the register select (RS) and enable (EN) lines respectively. Trimpot VR1 sets the display contrast voltage. Driving the transmitter The pump control signal appears at IC1’s RA4 (pin 3) output and is fed to the 433MHz transmitter. In practice, the Base Station can individually control up to 10 UHF Remote Control Main Switches, which in turn switch the pumps on and off as required. The data transmission protocol is as follows: initially a 50ms transmission is sent to set up the receiver so that it is ready to accept data. That done, a 16ms locking signal is sent, followed by a 4-bit encode number and a 4-bit tank number. An 8-bit pump-on or pump-off signal is then sent. This is either 162 for pump-on or 150 for pump-off. Finally, an 8-bit stop code with a value of 204 is sent. These stop bits indicate that the Installing The 433MHz Receiver & Transmitter Modules These larger-than-life-size photos clearly show how the receiver (top) and transmitter (right) modules are installed on the main PC board. You can leave the transmitter module out if you don’t intend to use the pump control feature. signal is for pump control and differ from those used for the transmissions from the Water Tank Level Meters. IC1, the LCD module and the 433MHz transmitter and receiver modules. Power supply The Water Tank Level Meter Base Station is built using two PC boards – a main board coded 04101081 (115 x 65mm) and a switch board coded 04101082 (63 x 15mm). The latter carries just four pushbutton switches (S1-S4) and two 4-way SIL header strips. These boards are housed in a bulkhead style case fitted with a clear lid and measuring just 120 x 70 x 30mm. Note that if you intend including Power for the circuit comes from an external 9-12V DC plugpack supply. Diode D1 provides reverse polarity protection, while zener diode ZD1 clamps any voltage spikes to 16V. A 10W resistor in series with the supply rail provides current limiting. A 100mF capacitor decouples the supply rail which is then fed to 3terminal regulator REG1. This produces a regulated +5V supply rail, with further supply bypassing provided by another 100mF capacitor directly across REG1’s output. Additional 100mF, 10mF and 100nF bypass capacitors are also used to decouple the supply to microcontroller Construction Capacitor Code Value mF Code IEC Code EIA Code 100nF 0.1mF 100n 104 Resistor Colour Codes (Receiver) o o o siliconchip.com.au No. 1 1 Value 1kW 10W 4-Band Code (1%) brown black red brown brown black black brown 5-Band Code (1%) brown black black brown brown brown black black gold brown January 2008  85 The LCD and switch modules simply plug into their respective socket strips on the main PC board. pump control, then the 433MHz transmitter and its associated components must be installed. Begin construction by checking the PC boards for any defects such as shorted tracks or breaks in the copper areas. That done, check that the hole sizes are correct. In particular, the holes for the four corner mounting screws, the four LCD mounting points and for REG1 should be 3mm in diameter. Check also that the main PC board fits into the box. It should have a circular cut-out at each corner so that it clears the corner pillars. If necessary, cut these out and file the edges of the board until it is a neat fit. That done, you can now begin installing the parts. Fig.2 shows the parts layout diagram. Install the two resistors first, taking care to use the correct value at each location. It’s just a matter of using a digital multimeter to check their values, before soldering This view shows how the 3-way & 4-way pin headers are installed on the switch board – see text. them in position. The three wire links can go in next, followed by PC stakes for the receiver antenna connections. You should also install additional PC stakes for the transmitter antenna connections if pump control is to be used. Follow these with diode D1 and zener diode ZD1, taking care with their orientation. That done, install a socket for IC1, making sure that the notched end goes to the left; ie, towards the 100nF capacitor. Don’t install IC1 yet, though – that step comes later, after some initial power supply checks. Next on the list are the 4-way and 3-way SIL (single in-line) sockets (used later to mount the switch PC board). These two sockets can be made by using a sharp knife to cut down an 8-pin DIL (dual in-line) IC socket. Clean up the edges with a small file before mounting the sockets. Similarly, you also need to install two 7-way SIL socket strips to accept the connections for the LCD module. These can be made by cutting and filing a 14-pin DIL IC socket. Now for the capacitors. Note that three of these are electrolytic types and must be oriented with their polarity as shown. In addition, the 100mF capacitor to the right of IC1 must lie horizontally on the PC board; ie, it’s installed with its leads bent down by 90° (see photo). Note also that there are three 100nF capacitors on the board. The two ceramic types go in adjacent to the 433MHz receiver and transmitter modules, while the 100nF MKT capacitor is positioned immediately to the left of IC1. Regulator REG1 is installed so that its metal tab sits flat against the PC board. The procedure here is to first bend the regulator’s centre lead down through 90° some 5mm from its body, after which its two outer leads can be bent down about 7mm from the body. That done, the device is fitted to the board and fastened using an M3 x 6mm screw and nut before soldering its leads. Don’t solder the leads before bolting the device to the PC board. If you do, you could stress and fracture the PC tracks as the device is tightened down. The DC socket, BCD switch S5 and trimpot VR1 can now go in. Be sure to orient the BCD switch exactly as shown and set it to the same number as the encode switches in the Water Tank Level Meters. 433MHz modules The main board assembly can now be completed by installing the 433MHz receiver and transmitter modules. As previously stated, the latter is only necessary if pump control is required, otherwise simply leave it out. Make sure that these parts are correctly oriented (see photos) – their pins are clearly marked. You will also need to install the antennas for these modules. These antennas are made using 170mm lengths of hook-up wire, each running from its module’s antenna PC stake to a PC stake at the opposite corner of the board. Switch board The switch board should only take a few minutes to assemble. Begin by installing the four push86  Silicon Chip siliconchip.com.au JOIN THE TECHNOLOGY AGE NOW with PICAXE This tab on the back of the LCD module must be bent flat against the PC board, in order to clear PIC micro IC1. Fig.3: the LCD module plugs into the 14-way DIL header and is supported on four M3 x 10mm tapped Nylon spacers. button switches, making sure that each switch has its flat side oriented as shown. That done, the 3-way and 4-way headers can be installed. These headers are installed on the track side of the PC board (see photo). Install each one so that its pins protrude about 1mm above the board surface, then solder the pins and slide the plastic spacer towards the PC board until it rests against the solder joints. The assembled switch board can then be plugged into the main board. Mounting the LCD module The LCD module is connected in similar fashion to the switch board. In this case, you have to carefully solder a 14-pin DIL header to the module and once again, this has to be installed from the underside of the PC board. Push the header in so that its pin length below the PC board is exactly 8mm (an 8mm-wide cardboard strip makes a handy alignment tool). That done, carefully tack solder a couple of pins, make any adjustments as necessary, then complete the soldering. Note that you will need a soldering iron with a very fine tip for this job, to avoid butchering the fine tracks on the top of the LCD module. Applying power Now for the smoke test. This is done with IC1 out of its socket and the LCD module unplugged. siliconchip.com.au First, apply power and check that there is 5V between pins 14 & 5 of IC1’s socket. If this is correct, switch off and install IC1 with its notched end towards the 100nF capacitor (see Fig.2). Next, install four M3 x 10mm tapped Nylon spacers on the main board to mount the LCD module. Secure these using M3 x 6mm screws, then plug the LCD module in and secure it to the spacers using another four M3 x 6mm screws. Note that there is a tab beneath the LCD module which interferes with IC1 when you attempt to mount the module in place. This tab must be bent over to lie flat against the LCD module’s PC board to avoid this problem. The completed assembly can now be installed in its case. If you are building from a kit, the case will probably be supplied with a screen-printed label and with all the necessary holes drilled. If not, then you will have to drill the holes yourself. You will need four 10mm holes in the lid of the case to clear the switch caps, plus a 6mm hole in the side of the case to give access to the DC socket. The latter is located 9mm down from top of base and 12mm in from the side. The switch holes in the lid can be drilled using the front panel label shown in Fig.4 as a template. These can initially be drilled out to about 5mm using a small pilot hole to start Developed as a teaching tool, the PICAXE is a low-cost “brain” for almost any project Easy to use and understand, professionals & hobbyists can be productive within minutes. Free software development system and low-cost in-circuit programming. Variety of hardware, project boards and kits to suit your application. Digital, analog, RS232, 1-Wire™, SPI and I2C. PC connectivity. Applications include: Datalogging Robotics Measurement & instruments Motor & lighting control Farming & agriculture Internet server Wireless links Colour sensing Fun games Distributed in Australia by Microzed Computers Pty Limited Phone 1300 735 420 Fax 1300 735 421 www.microzed.com.au January 2008  87 Parts List 1 PC board, code 04101081, 115 x 65mm 1 PC board, coded 04101082, 63 x 15mm 1 bulkhead case with clear top, 120 x 70 x 30mm (Jaycar HB6082 or equivalent) 1 9VDC 200mA plugpack 1 LCD module with backlight (Jaycar QP-5516 or equivalent) 1 PC-mount 2.5mm DC socket 1 433MHz receiver module (Jaycar ZW-3102 or equivalent) 1 433MHz transmitter module (Jaycar ZW-3100 or equivalent) (optional for pump control) 4 click-action PC-mount switches (S1-S4) 1 0-F 16-position BCD switch (S5) 1 14-pin DIL header (2.54mm pin spacing) 1 4-way SIL header (2.54mm pin spacing) 1 3-way SIL header (2.54mm pin spacing) 1 14-pin DIL IC socket (cut to suit the 14-pin DIL header) 1 8-pin DIL IC socket (cut to make 4-way & 3-way SIL sockets) 1 18-pin DIL IC socket 4 M3 x 9mm or M3 x 10mm tapped Nylon spacers 9 M3 x 6mm screws 1 M3 nut 4 No.4 x 6mm self-tapping screws 1 80mm length of 0.7mm tinned copper wire 1 170mm length of medium-duty hookup wire 1 170mm length of mediumduty hookup wire (optional for pump control) 2 PC stakes 2 PC stakes (optional for pump control) 1 10kW horizontal trimpot (code 103) (VR1) Semiconductors 1 PIC16F88-I/P microcontroller programmed with water tank level receiver.hex (IC1) 1 7805 5V regulator (REG1) 1 1N4004 1A diode (D1) 1 16V 1W zener diode (ZD1) Capacitors 3 100mF 16V PC electrolytic 1 10mF 16V PC electrolytic 1 100nF MKT polyester 1 100nF ceramic 1 100nF ceramic (optional for pump control) Resistors (0.25W, 1%) 1 1kW 1 10W Fig.4: this full-size front-panel artwork can be photostated and used as a drilling template for the case lid. The panel artwork can also be downloaded from our website, printed out and attached to the lid using double-sided adhesive tape – see text. 88  Silicon Chip with and then carefully reamed out to 10mm. That done, the front-panel artwork can be downloaded from the SILICON CHIP website, printed out on a colour printer and attached using doublesided adhesive tape. It can then be protected by using a single layer of clear self-adhesive film (eg, wide sticky tape) and the holes cut out with a sharp utility knife. Alternatively, you can trim the label to fit inside the lid by making cutouts for the four corner pillars. It can then be attach­ ed using a smear of clear silicone sealant. The board assembly simply sits on integral standoffs on the bottom of the case and is secured using No.4 self-tapping screws. That done, apply power, and adjust trimpot VR1 for optimum contrast on the LCD. The assembly can now be completed by attaching the lid and mounting brackets using the four screws supplied with the case. Setting up At this stage, when power is applied, the display should show a question mark (ie, “?”) for tank 1’s level. You now need to enable the tanks that are to be monitored using the procedure described earlier. Once that’s done, the correct level will be displayed for each tank. The Base Station needs to be positioned so that it can receive signals from all the Water Tank Level Meters that are to be monitored. In each case, when a valid signal is received, the display will show the signal level for that tank instead of a question mark. During our trials, we found that there were places inside the house where the reception was unreliable, particularly when the Water Tank Level Meter was more than 100m away. In practice, it’s a matter of finding the best place to receive signals from all the level meters. In addition, it may be necessary to position each level meter so that it is on the side of the tank that faces the Base Station. The antenna can also play a role here and an antenna consisting of a length of 1mm wire that extends straight out of the Water Tank Level Meter (ie, from the transmitter) can improve reception at the Base Station. Some experimentation with the antenna orientation may also be SC necessary. siliconchip.com.au