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Speedo Corrector, Mk.3 By JOHN CLARKE Correct your car’s speedo after swapping the wheels, gearbox or differential If you have swapped your car’s instrument panel, gearbox or differential with one from a different vehicle, your speedometer and odometer may no longer be correct. The same thing applies if you have fitted wheels or tyres with a different diameter. The solution is to use our updated Speedo Corrector which can increase or decrease the indicated speedometer reading. It operates from 12V or 24V DC and is simple to set up. I F YOU HAVE made any of the aforementioned modifications to your vehicle, you will almost certainly need to correct the speedometer and odometer readings. The Speedo Corrector can adjust your vehicle’s speedometer to show the correct road speed. It will work with analog or digital speedometers that use a frequency signal for speed sensing. It will not work with older speedometers that use a mechanical cable unless you make a new speed pick-up with Hall Effect sensor and Main Features • Allows alteration of speedo reading so that it reads faster or slower over a wide range • Caters for three input signal types • Automatic or manual set-up of input signal type • LED indication of valid speed sensor signal being received during set up • 12V or 24V operation (set using a link) • Adjustable response rate to compensate for speedo lag and output • LEDilicon 32  S Chipvoltage rate adjustment indication magnets on a driveshaft. Nor will it work with some the latest vehicles that have speedometers that connect to the Controller Area Network (CAN) bus instead of using a dedicated speedometer signal. CAN bus is a communications system between sensors and instruments in the vehicle. The Speedo Corrector intercepts the signal from the speed sensor and then increases or reduces its frequency before it is applied to the speedometer. Note that the Speedo Corrector will not correct for non-linearities in the speedometer but fortunately most speedometers are proportional in the region of 40-100km/h and so correcsiliconchip.com.au Par t s Lis t The compact PCB assembly clips into a UB5 plastic utility box. An on-board trimpot allows its output pulse frequency to be adjusted so that the car’s speedo matches the speed read-out on a GPS. tion at one speed in this region should provide the correct speed reading at other speeds. You will need to be able to access the speedometer signal in your vehicle to be able to install the Speedometer Corrector. This may require disassembly of the dashboard or steering column (see below). Optimistic readings With most unmodified vehicles running with standard sized tyres, the speedometer will tend to read optimistically, showing a higher than actual speed. So a speedometer indication of 100km/h could mean you are actually travelling between 87.27km/h and 100km/h, depending on the particular speedometer’s accuracy. That’s because the Australian Design Rules (ADR) (ADR18/00 and ADR18/03) specify speedometers to have an accuracy that is within +10% +4km/h for speeds above 40km/h. Alternatively, at an actual speed of 100km/h, your speedometer could read anywhere between 100km/h and 114km/h and still be within ADR specs. Vehicles manufactured before 1995 are worse and could have speed­ ometers that are within ±10% of the actual speed. Should the speedometer be within the pessimistic 0-10% range, then the speedometer will show a slower speed than you are actually travelling. That means that you could inadvertently exceed the legal speed limit and risk a hefty fine or loss of licence. In that case, the speedometer certainly needs to be corrected so that it shows the true speed! siliconchip.com.au Note that the odometer in a vehicle is required to have an accuracy within ±4%. For a modified vehicle, the odo­ meter will require correction to bring it to within the ADR spec. Elsewhere in this issue, we have an article on head-up display (HUD) speedos based on GPS or the vehicle’s OBDII (on-board diagnostics) socket. However, while these devices will give you a more accurate speed reading than the vehicle’s speedometer, they will not correct the odometer which our Speedo Corrector can do, to bring it within the required accuracy range. That way, upon resale of the vehicle, the correct vehicle mileage will be shown. Both the speedometer and odometer use the same speed signal that’s taken either from a sensor in the gearbox or a wheel sensor that is also used for the anti-lock braking system (ABS). The common signal for both speedo and odometer means that altering the sensor signal will change both the odometer and speedometer readings. Australian Design Rules mean that the speedometer is typically less accurate than the odometer but the Speedo Corrector Mk.3 (ideally) should be calibrated for both to be within the ADR specification. A GPS speedometer can be used as a guide to the correct speed adjustment while roadside odometer check signs can verify the odometer accuracy. The Speedo Corrector Mk.3 is a major revision of the Speedo Corrector published in the December 2006 issue of SILICON CHIP. This new version is considerably smaller, making it easier 1 double-sided PCB, code 05109131, 78 x 46mm 1 UB5 box, 83 x 54 x 31mm (translucent blue, clear, black or grey) 2 2-way PCB-mount screw terminal blocks, 5.08mm pitch (CON1) 1 DIL18 IC socket 1 7 x 2 DIL pin header (2.54mm pitch) broken into 4-way & 3-way headers (JP2,JP3) 1 5-pin SIL header (2.54mm pitch) broken into 3-way & 2-way headers (JP1,LK4) 1 10kΩ 20-turn top-adjust trimpot (VR1) 1 10kΩ miniature horizontal mount trimpot (VR2) 5 jumper shunts 1 20MHz crystal (X1) 1 M3 x 10mm screw 1 M3 nut & shakeproof washer Semiconductors 1 PIC16F88-E/P microcontroller programmed with 0510913A. hex (IC1) 1 LM2940CT-5 TO-220 5V low dropout regulator (REG1) 4 BC846 (SOT23) NPN SMD transistors (Q1,Q2,Q3,Q5) 2 BC857 (SOT23) PNP SMD transistors (Q4,Q6) 1 15V 1W zener diode (ZD1) 1 8.2V 1W zener diode (ZD2) 1 bi-colour (red/green) 3mm or 5mm LED (LED1) 2 PC stakes (TPG & TP4) Capacitors 2 100µF 16V PC electrolytic 3 1µF monolithic multi-layer ceramic (MMC) 1 10nF MKT 1 1nF MKT 2 33pF NP0 ceramic Resistors (0.25W, 1%) 1 6.8kΩ 1 220Ω 0.5W 2 1kΩ 1 10Ω Resistor arrays 2 5-way 10kΩ resistor arrays (4610X-102-103LF) 1 4-way 1kΩ resistor array (4608102-102LF) to install in a vehicle. It now operates from 12V or 24V and includes the original features such as automatic or September 2013  33 Specifications Output ratio: adjustable from 1 to 1/6 the rate for lower output frequencies and from 1 to 6 times for higher frequencies. Adjustment resolution: < 0.4% for 1x to 2x and 1x to ½x adjustments; < 0.8% for 2x to 4x and ½x to ¼x; < 1.8% to x6 and x1/6 Minimum input or output operating frequency: 1Hz. Maximum input & output frequency to maintain maximum adjustment resolution: 1.2kHz. Response rate adjustments: 1s (fully anticlockwise), 500ms, 250ms (mid setting), 125ms and 62.5ms (fully clockwise) – set using VR2. Input and output types: pull-up, pull-down or AC. Output swing: 0-8.2V or 0-5V or 8.2V peak-peak AC or 5V peak-peak AC. Maximum input voltage: 50V RMS. Minimum input sensitivity: 0.7V peak (on high sensitivity setting); 2.5V peak (on low sensitivity setting). Power: 9-30V DC at 25mA. manual set-up to suit the speed signal sensor and an AC signal output to suit Nissan speedometers. The overall adjustment range has also been increased over the original version. And instead of using two expens­ive rotary switches (as in the 2006 version) to set the adjustment, we now use a low-cost multi-turn trimpot. A bi-coloured LED shows green for adjustments that increase the output frequency and red when the output frequency is reduced (with respect to the input signal). A test point is provided to allow a multimeter to monitor the amount of adjustment that’s set. Mechanical Speedo? The Speedo Corrector Mk.3 will work only on electronic speed­ o­ meters, ie, those that don’t have a mechanical rotating cable driving them. If you have an older car with a mechanical speedo, then you won’t be able to correct it – at least not using this circuit. Non-Linearity? The Speedo Corrector Mk.3 will not compensate for non-linear errors. In other words, if the speedo reads 10% high at 25km/h and 4% high at 100km/h, you won’t be able to use the Speedo Corrector Mk.3 to get the speedo accurate at all speeds. However, most speedo errors are proportional and so can be dialledout with the Speedo Corrector Mk.3. 34  Silicon Chip In practice though, it is usually not necessary to monitor the degree of adjustment. The relevant trimpot (VR1) is simply adjusted so that the speedometer or odometer reads correctly, compared with a GPS speedo or roadside odometer check markers (at 1km intervals). The Speedo Corrector is housed in small plastic case measuring 82 x 53 x 30mm. It can be concealed anywhere underneath the dashboard. Circuit description Fig.1 shows the circuit which is based on IC1, a PIC16F88-E/P microcontroller. It’s programmed to alter the incoming speed signal frequency by a factor set using trimpot VR1. Transistors Q2, Q3 & Q4 are included to provide for speedometer sensors that require pull-up or pulldown resistors. Q3 & Q4 are turned on by RA4 (pin 3) to provide pull-up via a 1kΩ resistor or Q2 is turned on by RA3 (pin 2) to pull the same resistor down, or all the transistors are left turned off if no pull-up or pull-down is required (in the case of an AC sensor). Whether or not Q2, Q3 & Q4 are turned on is controlled by IC1 in response to the links for JP2, connected to its RB2, RB4, RB5 & RB7 pins (8, 10, 11 & 13). As well as providing options for pull-up, pull-down etc, there is an ‘Autoset’ mode whereby the Speedo Corrector software will select each setting one at a time until the micro gets a satisfactory signal. With each selection, the program waits to check if it receives at least 20 cycles of signal within a 1-second period. If not, it moves on to the next selection. When it does receive signal, that input selection is stored in memory and used thereafter. Manual selection via the jumper links is provided for installers of the unit who already know the required input condition for particular vehicles. Manual selection can also be used should the automatic Autoset not work successfully on your vehicle. All the resistors on the circuit marked with an asterisk (*) are in resistor arrays: two 10-pin arrays comprising five 10kΩ resistors in each and a single 8-pin array comprising four 1kΩ resistors. The arrays save space on the PCB. After being pulled high, low or neither, the input signal is fed to the base of Q1 via a low-pass filter consisting of a 10kΩ resistor and 10nF capacitor and then via another 10kΩ resistor. A 6.8kΩ resistor at the base of Q1 can be either connected to 0V or left floating under the control of the RA2 output of IC1. When floating, Q1 will be switched on with a 0.7V input signal, corresponding to the high-sensitivity setting. When the 6.8kΩ resistor is connected to 0V, the signal level required to switch Q1 is increased to about 2.5V (the low sensitivity setting). The signal at Q1’s collector is filtered with a 1nF capacitor and fed to the RB0 input, pin 6, of IC1. This has an internal Schmitt trigger to ensure a clean signal. The microcontroller then increases or decreases the signal frequency according to the program and feeds it out from its RB1 output at pin 7 to the base of transistor Q5. Q5’s collector load is a 1kΩ resistor connected to the +8.2V or +5V supply, as selected by link JP1. Q5 drives Q6 which has two paralleled 1kΩ resistors (in the 8-pin resistor array, mentioned above). This is done to provide a relatively low impedance pull-down output. Links at JP3 provide the options for pull-down, pull-up or AC-coupling for the output signal. Note that the pullup signal comes from the collector of Q5 while the pull-down or AC signal comes from the collector of Q6. VR1 is used to set the degree of speedometer correction. The voltage at VR1’s wiper is applied to the AN0 input of IC1 and is converted to a 9-bit digital value. With the wiper centred, the speed signal passes through unchanged. Winding the trimpot clocksiliconchip.com.au LK4 10Ω +12V/ +24V 220Ω 0.5W REG1 LM2940-5T A K GND 1 µF ZD1 15V 1W +8.2V K 100 µF 16V MMC LK4 IN = 12V LK4 OUT = 24V 0V JP1 +5V OUT IN ZD2 8.2V 1W 1 µF MMC A +5V E Q4 BC857 10k* B 1k C C Q3 BC846 1k* B 10k* 3 6 10k B C Q1 BC846 RB4 RA4 RB7 RB0 1nF RA0/AN0 1 RA2 IC1 PIC1 6F8 8 PIC16F88 -E/P 2 E 10 X1 20MHz * PART OF RESISTOR ARRAY ZD1, ZD2 A 33pF 33pF 16 VR2 10k 4 = AUTOSET 17 1 µF 1k* 18 10k* λ 12 AR OSC2 RB 3 /PWM Vss 10k 7 RB1 5 RESPONSE 3 = PULLDOWN 8 RB6 OSC1 (20T) 2 = AC 13 TP2 15 1 = PULLUP MMC RA1/AN1 RA3 VR1 10k ADJUST JP2 11 TP1 10k* B RB5 RB2 6.8k Q2 BC846 Vdd C E 10nF 14 4 MCLR TP3 E 10k IN 10k* 10k* λ B E LED1 C 100 µF Q5 BC846 KR E Q6 BC857 2x 1k* 10k* 1k 9 1 2 3 1 = PULLUP JP3 2 = AC 3 = PULLDOWN TP4 TPG C B K OUT LM2940T-5V LED1 SC 2013 SPEEDO CORRECTOR MK3 KR AR BC846, BC857 C B E GND IN GND OUT Fig.1: the circuit is based on PIC microcontroller IC1. It takes the speedo signal and multiplies it according to the setting of trimpot VR1. The speedo signal frequency can be either increased or decreased. wise increases the signal frequency while winding it clockwise reduces the frequency. The bi-coloured LED (LED1) connected between pins 9 & 12 indicates frequency increase or decrease, as previously mentioned. When VR1 is set at mid-setting, both the red and green sections are driven equally and the resulting orange colour indicates ‘no change’ in output frequency, corresponding to a 50% duty cycle of the 19kHz pulse width modulation (PWM) signal at pin 9. At the same time, the voltage at test point TP4 will be at 2.5V. For other settings of VR1, the RB6 output at pin 12 will be either low or high; low for green and high for red. The LED brightness will vary slightly with the PWM duty cycle but this is siliconchip.com.au not sufficient to gauge the degree of adjustment off centre for VR1. Setting speedometer response Different speedos respond at different rates to a change in the signal frequency. The Speedo Corrector Mk.3 can compensate for this by varying its response period which can be adjusted from between 1s and 62.5ms. The required setting used depends on the response of the speedometer when the vehicle comes to a stop. If the speedometer takes too long to drop back to zero with a 1-second response, then it should be reduced with trimpot VR2. IC1 operates at 20MHz using crystal X1. This frequency was chosen so that the software program runs sufficiently fast to operate with speedometer signals up to 1.2kHz. Note that the Speedo Corrector Mk.3 will operate with signals above 1.2kHz but the accuracy of correction will be reduced. An internal power-on reset for IC1 is provided using the MCLR-bar input at pin 4 and is connected to the 5V supply via a 1kΩ resistor. This keeps the IC reset until the power supply voltage is correct. Power for the circuit is applied via a 10Ω resistor and a 15V zener diode (ZD1) to an LM2940-5T 5V automotive regulator, REG1. For 12V operation, ZD1 is shorted out with link LK4. For 24V operation, LK4 is removed and ZD1 effectively subtracts 15V from the supply applied to REG1. An 8.2V supply is provided using ZD2 and the 220Ω resistor. This supply September 2013  35 JP2 1 Pullup 2 AC 3 Pulldown 4 Autoset 10nF SPEEDOMETER 1nF CORRECTOR JP3 1k ARRAY2 5x10k 10Ω LED1 3 JP3 1 Pullup 2 AC 3 Pulldown LK4 out 24V BREAK OUT FOR CABLE GLAND CLEARANCE TP4 ARRAY1 CON1 IN OUT 0V +12/24V 6.8k TP1,2,3 1 2 15V 1 3 4 220Ω JP2 AR ZD1 IC1 PIC16F88 JP1 1 2 LK4 1 µF 1 µF VR1 1 µF LM2940 8.2V +5V 1k X1 +8.2V VR2 1 µF 05109131 C 2013 REG1 BREAK OUT FOR CABLE GLAND CLEARANCE 33pF 1 3 105109131 90150 100 µF ZD2 33pF TPG ARRAY3 4x1k BC857 Q6 Q5 Q4 Q3 Q2 Q1 100 µF BC846 TOP VIEW OF PCB BOTTOM VIEW OF PCB Fig.2: follow these two diagrams to build the unit, starting with the six SMD transistors (Q1-Q6) on the back of the PCB. Install link LK4 for 12V operation or remove it for 24V operation. The other linking options are explained in the text. ALTERNATIVE TO RESISTOR ARRAY USING SINGLE RESISTORS Fig.3: single resistors mounted end-on can be used instead of the resistor arrays. You would need 10 x 10kΩ and 4 x 1kΩ resistors. can be selected to give a higher signal output from the corrector which is necessary for reliable operation with some speedometers. Construction The Speedo Corrector is built onto a double-sided PCB with plated through holes. This board is coded 05109131, measures 78 x 46mm and is designed to clip into a plastic UB5 box measuring 83 x 54 x 31mm. A hole is made in one end of the box to allow a cable gland to be fitted to allow wire entry (input and output signals plus supply leads). Alternatively, the leads can be run out through a grommet and restrained inside the box using a cable tie. If you intend fitting a cable gland, it will be necessary to snap off a breakaway section located at one end of the PCB, to allow space for the cable gland nut inside the box (see photo). Fig.2 shows the parts layout on the PCB. First, check the PCB for any faults (rare), then start the assembly by installing the six SMD transistors on the underside of the PCB. Note that Q1, Q2 & Q5 are BC846s, while Q4 & Q6 are BC857s, so be careful not to get them mixed up. You will need a good light (preferably a magnifying lamp) and a finetipped soldering iron for this job. The procedure is straightforward: carefully place transistor Q1 in position, hold it down with some tweezers and solder one of its leads first. That done, make sure that it’s positioned correctly (remelt the solder and nudge it if necessary) before soldering the other two pins. Repeat this procedure for the remaining five SMD transistors, taking care to fit the correct type to each location. Once the SMD devices are all in place, flip the board over and install the single resistors and zener diodes. Table 1 shows the resistor colour codes but it’s a good idea to check each one using a digital multimeter before soldering it into position. Make sure that the zener diodes are installed with the correct polarity, ie, with the banded ends orientated as shown on Fig.2. Don’t get these two devices mixed up – ZD1 is a 15V zener, while ZD2 is an 8.2V zener. Table 1: Resistor Colour Codes o o o o o No.   1   2   1   1 36  Silicon Chip Value 6.8kΩ 1kΩ 220Ω 10Ω 4-Band Code (1%) blue grey red brown brown black red brown red red brown brown brown black black brown There are two PC stakes to be installed and these go in at test points TPG and TP4. PC stakes are not installed at TP1, TP2 & TP3, as these test points can be monitored by touching a multimeter probe on the plated PCB pads provided. Resistor arrays The resistor arrays are labelled 10X2-103 (5 x 10kΩ) and 8X-2-102 (4 x 1kΩ). These can be installed now and can go in either way around. Alternatively, you can use single resistors mounted end-on in place of the arrays, as shown in Fig.3. You would need to install 10 x 10kΩ resistors instead of the two 5-way arrays and 4 x 1kΩ resistors instead of the 4-way array. The 20MHz crystal (X1) and an 18pin IC socket for IC1 can be fitted next. The socket must be orientated with its notched end towards the adjacent edge of the PCB. Follow with regulator REG1; it’s mounted horizontally and secured with an M3 screw, shakeproof Table 2: Capacitor Codes Value 1µF 10nF 1nF 33pF µF Value IEC Code EIA Code 1µF 1u0 105 0.01µF 10n 103 0.001µF   1n 102 NA 33p    33 5-Band Code (1%) blue grey black brown brown brown black black brown brown red red black black brown brown black black gold brown siliconchip.com.au Take care to ensure that microcontroller IC1 and the other polarised parts are orientated correctly and don’t get the SMD transistors mixed up. The signal and power leads exit the case through a cable gland, as shown at right. washer and nut. Bend its leads at right angles before installing it and be sure to tighten it’s mounting screw before soldering the leads. Don’t do this in reverse order. If you solder the leads first, you could crack the PCB tracks as the mounting screw is tightened down. Now for the capacitors. The ceramic and MKT types can go in either way around but the 100µF electrolytic must be orientated as shown. The 4-way and 3-way dual-in-line pin headers for JP2 and JP3 are next. Push them all the way down onto the PCB before soldering their leads. Indicator LED LED1 is mounted so that it sits directly on (or very close) to the PCB. Make sure it’s orientated correctly with its anode (longer lead) going to the pad marked ‘AR’. That done, install trimpots VR1 & VR2 and the 4-way screw terminal block. VR1 is mounted with its adjusting screw towards the crystal. The 4-way screw terminal block is made by dovetailing two 2-way terminal blocks together. Push it all the way down onto the PCB and make sure its wire entry holes face outwards before soldering the pins. Initial tests Before plugging IC1 into its socket, connect a jumper across LK4 and apply 12V to the circuit (ie, between the 12/24V and the 0V input terminals). That done, check that the voltage between pins 5 & 14 of IC1’s socket is around 5V (you should get a reading that’s between 4.85V and 5.15V). If this is correct, disconnect the siliconchip.com.au power and plug microcontroller IC1 into its socket, taking care to orientate it correctly. Make sure that none of the IC’s pins are bent under the socket or splayed down the side during this procedure. With IC1 now in place, reapply power and adjust VR1 to its mid setting. This is indicated when both the green and red colours in LED1 flash. If the LED is red, rotate VR1 clockwise to reach mid setting. If the LED is green, rotate VR1 anticlockwise until mid setting is reached. Installing the jumpers Before installing the Speedo Corrector in your vehicle, you need to fit the relevant jumper links. First, either leave the jumper on LK4 for 12V operation or remove it for 24V operation. That done, install jumper JP1 in the 5V position but don’t fit a jumper to the JP3 header yet. Most readers should also install a jumper in position 4 on header JP2 (ie, in the Autoset position) for automatic setting up. The response trimpot (VR2) should initially be set fully anticlockwise for a 1s response time. In some cases, you may already know the required jumper settings for the vehicle (eg, if you’ve already installed a Speedo Corrector Mk.3 in a similar vehicle). In that case, fit a jumper in position 1 of JP2 for pullup, position 2 for AC or position 3 for pull-down. Low-sensitivity AC requires jumpers in both positions 2 & 3 but ignore this for the time being. The JP3 setting needs to duplicate the JP2 selection, ie, a jumper in position 1 for pull-up, position 2 for AC and position 3 for pull-down. As stated though, if you don’t know the settings, fit a jumper to position 4 (Autoset) of JP2 and leave the jumper off JP3. Installation Now for the installation but first a word of warning: in some cars, it will be necessary to partially dismantle the dash in order to locate the power supply wirer and speed input wire to the speedo. If you need to disassemble any of the steering wheel section, take care if an air-bag installed as this will have to be disabled. Generally this means disconnecting the vehicle’s battery and waiting for a set period before it is safe to disassemble the column. However, check the manual for your car and make sure you know exactly what to do to disable the airbag before proceeding. If in doubt, don’t! In practice, the Speedo Corrector must be connected to either a 12V or 24V ignition-switched supply, with the 0V line going to chassis. Be sure to use automotive cable for these connections and make sure you connect to a fused supply rail (eg, for the accessories). The signal input wire to the speedo must be cut so that the Speedo Corrector Mk.3 can be inserted in-line with it. This wire will usually come either directly from a speed sensor or it may come from the ECU and you can generally find it in the dashboard space behind the speedometer. A wiring diagram for your vehicle will come in handy for tracking down this wire. Depending on the vehicle, removing the dashboard panels can be a difficult undertaking and may not be September 2013  37 5 TP4 Voltage Versus Output/Input Ratio 4.5 4 TP4 (V) 3.5 3 2.5 2 1.5 1 0.5 0 1/6 1/4 1 1/2 2 4 6 OUTPUT RATIO Fig.4: you can use this graph to determine the voltage that needs to be set at TP4 for a given frequency output ratio. It works in reverse too – if the Speedo Corrector has been adjusted using a GPS, you can determine the output ratio from the graph after first measuring the voltage on TP4. something you want to do. In that case, tracking down the speed signal wire elsewhere in the vehicle is the way to go but, of course, you will need a wiring diagram. In other cases, it may be possible to find the dashboard disassembly instructions on the internet, especially for older cars. Once you’ve located the speed signal wire, cut it and connect the Speedo Corrector Mk.3’s signal input to the lead coming from the speed sensor or ECU. The corrector’s output is then connected to the wire running to the speedometer. Initially, you should make the leads to the Speedo Corrector Mk.3 long enough so that it can be dropped down from behind the dash and easily accessed by someone sitting in the front passenger seat. Once it’s all wired up, Tacho As Well? The Speedo Corrector Mk.3 will also work with electronic tachos that take their feed from the ECU (ie, all cars with engine management). The configuration procedure is the same as for use of the device as a speed interceptor, except that the “speed sensor” becomes the tacho output signal from the ECU. This application is particularly suited to engine and gearbox swaps. 38  Silicon Chip you can jump straight to the calibration section below if you have already manually set up the jumper links. Alternatively, for Autoset, you have to follow these simple steps: (1) Start the engine and check that LED1 lights red. (2) Drive the car for a minute or so with a passenger (note: the speedo will not be working at this stage). (3) Wait until the LED flashes green at a 1-second rate. This shows that the Speedo Corrector Mk.3 has automatically set itself to cater for the type of speedometer signal that is present and is receiving a valid signal from it. (4) Once a valid signal has been received, get the passenger to remove the Autoset jumper. Note that the power must still be on when removing the Autoset jumper in order for the settings to be stored. If this has been successful, the LED should now alternately be flashing red and green to indicate that the unit is operating normally (although the speedo will still not be working). (5) If the LED doesn’t flash, check the signal wiring from the speed sensor. If the wiring is correct, try the 8.2V setting for JP1 and drive the vehicle again. (6) If it is still “no go”, try manually setting the jumpers on JP2 and JP3 (they have to agree) and test each setting in turn. First, remove the Autoset jumper, then start with the Pullup jumper option (ie, position 1 for both JP2 & JP3) and drive the vehicle to see if the speedo works. If it doesn’t, change the settings until the speedo works. Position 2 (AC) for both JP2 & JP3 can be selected next, followed by position 3 (Pulldown). The final selection to try is low-sensitivity AC, ie, install jumpers in both positions 2 & 3 of JP2 and in position 2 of JP3. (7) If you got the speedo working with the Autoset function, you now need to install a jumper at JP3. It’s just a matter of trying each jumper setting in turn until the speedometer starts working. Alternatively, you can determine the set-up by making some simple voltage measurements. TP2 will be at 5V if the selection is Pulldown, while TP3 will be at 5V if the selection is Pullup. For AC, both TP2 and TP3 will be at 0V. Test point TP1 OK, so what’s the purpose of test point TP1? It’s there so that if an Auto­ set sets the input for AC, TP1 can be checked to see if the associated 6.8kΩ resistor is tied to 0V for low sensitivity or left floating for high sensitivity. This may be of interest to installers so that they can check what the settings are for each vehicle. For example, if the voltage between TP1 and TPG reads 0V (with power applied), then input to the 6.8kΩ resistor is probably tied to 0V. However, if you place your finger on test point TP1 to inject noise and the voltage changes, then TP1 is floating. This means that the input to the 6.8kΩ resistor is also floating. Calibration You will need an accurate reference to correctly calibrate the speedo. This can be provided by a GPS unit or a GPS speedometer. Just make sure that you have an assistant make the necessary adjustment as you drive! It’s simply a matter of adjusting VR1 in the Speedo Corrector Mk.3 until speedo gives the correct reading (ie, agrees with the GPS). You can also use the odometer check distances that are marked on some roads to check the accuracy of the odometer. Alternative approach You can also adjust the Speedo Corrector for a certain ratio based on known wheel, differential or gearbox siliconchip.com.au Helping to put you in Control 4-Beam Photoelectric Detector Another view of the completed unit. Note how a small section at the righthand end of the PCB is snapped off to provide clearance for the nut that’s used to secure the cable gland. ratio changes. Basically, test point TP4 allows you to monitor the ratio between input and output frequency. This test point nominally sits at 2.5V when the input and output frequencies are equal but goes above 2.5V when the output frequency is higher than the input frequency. Conversely, TP4 goes below 2.5V when the output frequency is lower. Note that TP4’s voltage is non-linear with respect to frequency changes. The accompanying graph (Fig.4) shows the relationship between the voltage at TP4 and the output:input frequency ratio. So to set the unit for a known output ratio, simply use the graph to read off the required voltage for TP4. Trimpot VR1 is then adjusted to bring TP4 to this value. If a high degree of accuracy is required, measure REG1’s output (Vreg) and then multiply the voltage read off the graph by Vreg/5. You can also use Fig.4 to look up the ratio that’s been set using VR1 if you have calibrated the unit against a GPS. It’s just a matter of measuring the voltage at TP4 and then looking up the ratio on the graph. For best accuracy, multiply the TP4 reading by 5/Vreg before checking the ratio. Note that the voltage reading will not provide an extremely accurate value to calculate the adjustment setting. That’s because the PWM output is loaded by the indicating LED. Final trims If you have manually set the input selection for AC, you can experiment by also placing a low-sensitivity jumper in position 3 of LK2. This may result in smoother operation of speedometer siliconchip.com.au compared to when this jumper is left out. Select the setting that gives best results (ie, jumper in or out). Additionally, when there is an Autoset selection of AC (both TP2 and TP3 at 0V), the sensor signal may have required a pull-down setting in order to allow satisfactory operation at high speeds without dropping out. An inherent pull-down is provided by the 6.8kΩ resistor on the base of Q1 but this may not be sufficient to pull the signal down fast enough at high frequencies. If you experience speedometer drop-out at high speeds, try installing a jumper at position 3 for JP2 to give manual pull-down. Another possible problem is that the speedo may some show some lag when the vehicle abruptly comes to a stop from a slow speed. When this happens, the speedo may show a reading for up to 1s after the vehicle stops. Speedo lag could also be evident when moving off from a standstill. In this case, the speedo initially shows 0km/h before then suddenly jumping to the correct speed reading. This problem can be overcome by adjusting response trimpot VR2. At its full anticlockwise position, the response lag is 1s. As the trimpot is adjusted clockwise, the response becomes faster at 0.5s and then 0.25s at mid-setting. Further rotation provides 0.125s and then 62.5ms at VR2’s full clockwise position. The optimal setting is when the adjustment provides the shortest lag while still reliably operating the speedo at slow speeds. Once the Speedo Corrector is working properly, the lid can be attached and the unit tucked up behind the SC dash out of sight. Through-beam laser sensor consisting of a transmitter and receiver. Alarm output has normally open and normally closed contact, up to 250 m outdoor & 750 m indoor detection distance. 13.8 to 24 VDC powered SKU: KPR-121 Price: $92.97 + GST SMS NET Data Logger It features 8 digital inputs, 4 digital outputs & 8 temp. channels. Configuration is setup by GSM mobile phone or via Ethernet. Up to 10 different numbers can be preset in the system. 9 to 15 VDC powered. SKU: LEC-050 Price: $699 + GST DIN Rail Mount Step Pulser Controls speed & direction of 2 stepper motors. It features on-board potentiometer for speed control, mini joystick for motor run & direction. Output frequency is between 70 Hz to 4.8 kHz. 8 to 30 VDC powered. External inputs for buttons/joystick SKU: KTD-277 Price: $49.95 + GST Wired Glass Breakage Sensor The sensor is used as an input device to an alarm system. When a glass breakage frequency has been detected, it will trigger a signal to the alarm system. Detection range up to 7 m. 12 VDC powered. SKU: KPR-114 Price: $22.40 + GST 2.5 mm Universal Terminal Universal DIN Rail Screw terminal offers a wire section of 2.5 mm2 with 2 side cable entry. Suitable for U type rails, TH35-7.5 & G-type railway G32-15L, G32-18. Other sizes are also available. SKU: TRM-007 Price: $0.79 + GST IRTemp Sensor Module Remote temperature sensing module for your Arduino! It features; on-board voltage regulator, communications interface, measurement temperature range from -33 to 220 °C & 1s response time. 3 to 5 VDC powered. SKU: FRA-020 Price: $34.95 + GST Asymmetrical Cyclic Timer DIN-rail mount cyclic timer with configurable on and off times. Features selectable “pulse first” or “pause first” for initial timing function. 4PCO relay outputs, selectable multi-time range from 1s to 100 days. 12 to 250 VAC/VDC powered. SKU: NTR-110 Price: $74.95 + GST For OEM/Wholesale prices Contact Ocean Controls Ph: (03) 9782 5882 oceancontrols.com.au September 2013  39