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By JOHN CLARKE Shift Indicator & Rev Limiter For Cars If you drive your car for optimum performance, you will want this Shift Light Indicator to indicate just when to change gears. As a bonus, it incorporates a Rev Limiter which throttles back the fuel injectors. I F YOU ARE INTERESTED in driving your car for best acceleration or fuel economy, you will know that an engine’s torque peaks at a lower RPM than the peak power. You will also know that when driving for maximum fuel economy, it is wise to keep engine revs reasonably low and to get into the The gear shift and rev limit points are indicated by four LEDs. The LDR at far left is part of the dimming circuit. 66  Silicon Chip highest gear as soon as possible. But whether driving for best acceleration or economy, you don’t want to be watching the tacho to judge each gear change. That would distract your attention from the road. Having a Shift Light Indicator is the way to go. You will see LEDs light up without having to divert your eyes from the road. Our Shift Light Indicator has three LEDs to indicate shift points and a fourth LED for the Rev Limiter. How you set the individual LED RPM values is up to you. For example, you could set the three LEDs to give a ‘ready’, ‘set’ and ‘go’ indication for each gear change. Rev limiting can be hard or soft. Hard limiting simply switches off power to the fuel injectors and the engine immediately “dies”; power does not came back until the RPM falls below a threshold value. Soft limiting reduces the fuel injector duty cycle in stages so that the power is not killed abruptly. Either way, the engine is protected from damage due to over-revving. Note that many cars these days already have inbuilt rev limiting, so you may choose not to implement this feature. Connections The Shift Light Indicator (SLI) can either connect to the tachometer signal from the car’s ECU (engine control unit) or to the ignition coil where there is no ECU. We have catered for just about every conceivable engine configuration: 1 to 12-cylinder 4-stroke, 1 to 6-cylinder 2-strokes and 2 & 3-cylinder asymmetrical 4-strokes. Other connections required are +12V power, 0V (chassis), ground and to the fuel injectors. siliconchip.com.au Measuring engine revs We measure engine revs in RPM (revolutions per minute) by monitoring the tachometer signal from the car’s ECU. This delivers one pulse for every cylinder firing (ie, each spark plug firing). We also need to know the engine FULL SOFT LIMITING LIMIT LED4 ON (HARD LIMIT ON) LIMIT LED4 OFF (HARD LIMIT OFF) SHIFT3 LED OFF SHIFT3 LED ON SHIFT2 LED OFF SHIFT2 LED ON HYSTERESIS SHIFT1 START OF SOFT LIMITING Each shift point can be set and operates independently from the others. While the software has them labelled as Shift1, Shift2 and Shift3, they can each be set anywhere between 0 and about 12,500 RPM, in 25 RPM steps. Setting shift points is easy and is done with a trimpot that produces a voltage directly proportional to RPM. So if a shift point is required at 5500 RPM, you set the trimpot wiper to 0.55V. You then press a switch to store the value. The Shift LEDs light to indicate RPM at and above the stored values, as shown in Fig.1. An adjustment is provided to prevent them from flickering on and off when the RPM is hovering around the shift point. This adjustment causes the Shift LEDs to go out at an RPM lower than the shift setting. The difference in the thresholds is called the “hysteresis”. HYSTERESIS SHIFT2 SHIFT1 LED OFF Shift points HYSTERESIS SHIFT3 SHIFT1 LED ON The SLI unit can be located in a convenient location under the car’s dashboard while the separate display involving four high brightness LEDs can be mounted on the dashboard. The shift LEDs have automatic dimming so that they will not be too bright when driving at night but the Rev Limiter does not have dimming – when it comes on, you will be fully alerted! RPM HYSTERESIS (LIMITING) Fig.1: this diagram shows how the shift LEDs light to indicate RPM at and above the stored values. Note that a degree of hysteresis is built into each shift point, to prevent LED flicker at the critical values. type (2 or 4-stroke) and the number of cylinders in order to calculate engine RPM. For example, a 4-cylinder 4-stroke engine has two cylinder firings per revolution, a 6-cylinder has three firings, a V8 has four firings per rev and so on. A particular problem in measuring engine RPM is that we cannot just count pulses over a one minute or even 10-second period. That would mean that the SLI just would not react fast enough. Instead, we could use a 300ms period which gives a count of 10 for a 4-cylinder 4-stroke engine running at 1000 RPM. But even this period is too long when you consider how fast engine RPM could change – it could easily go from 1000 RPM to 6000 RPM or more, in that short time. In addition, a counting period of just 300ms means that the RPM cannot be measured accurately. That previous count of 10 pules might mean the RPM is 900 or 1100 RPM, a 200-RPM uncertainty – not very good. There is a better way, as shown in Fig.2, the block diagram of the cir­cuit. Here the RPM signal from the engine is filtered to prevent triggering on transient signals and then instead of counting the pulses, we measure How Rev Limiting Is Achieved T HIS PROJECT achieves rev limit­ ing by cutting power to the fuel injectors and this involves switching the injector positive (+12V) supply rail. This can be done using one of two methods – either by using a relay to switch the supply for hard limiting or by pulse width modulating power Mosfets to give soft limiting – ie, a gradual reduction in engine power. Fig.7(a) shows the standard fuel injector setup. As can be seen, the positive terminals of the fuel injectors are all connected to a common +12V supply rail. The engine management siliconchip.com.au computer (ECU) switches the negative side of each injector. Hard limiting is achieved by wiring the relay in series between the positive terminals of the fuel injectors and the +12V injector supply rail. This relay, which is controlled by the limiter circuit, switches off the injectors (by opening its contacts) when the rev limit is reached and this immediately cuts engine power. Fig.7(b) shows this scheme. Alternatively, soft limiting is achieved by wiring two parallel power Mosfets in series between the fuel injectors and the +12V injector supply rail. These Mosfets are then pulse width modulated (PWM) by the limiter circuit when the rev limit is reached, which means that the injector supply rail is also pulse width modulated. The higher the revs go, the lower the PWM duty cycle. As a result, the engine power is gradually reduced when the rev limit is reached. Fig.7(c) shows this scheme. Why do we also include the relay in the soft limiting circuit? It’s there for added reliability, as explained in another panel. February 2008  67 SHIFT1 (LED1) COMPARE IC1 PIC 16F88-I/P RPM SIGNAL FILTERING RB0 CAPTURED COUNTER VALUE COUNTER SHIFT 1 SETTING RA6 SHIFT 2 SETTING SHIFT2 (LED2)  RA7 COMPARE RPM SHIFT3 (LED3) SHIFT3 SETTING 2MHz SIGNAL RPM FACTOR RA0 HARD/SOFT LIMITING RB4 RB1 RB3 RB2 LIMIT (LED4) COMPARE 8 4 2  COMPARE AVERAGE S3 BCD SWITCH ENGINE FORMAT  1 LIMIT SETTING COM  RA1/ RA2 Fig.2: block diagram of the Shift Indicator & Rev Limiter. It measures RPM by using the tacho signal to gate a 2MHz signal into a counter. The counter value is then divided into the RPM factor as set by BCD switch S3 to give engine RPM. the time between them, using a 2MHz signal. What happens is that each firing pulse gates the 2MHz signal to a counter. The next pulse places the count in memory and clears the counter which then proceeds to count again. For example, if the RPM signal is 33.333Hz, the counter will reach 60,000 between pulses. This value is divided into the RPM factor which for a 4-cylinder 4-stroke engine is 60 million. So in this case, the result of the division is 1000 RPM. Each RPM calculation takes 888ms; well before a new count is available. This RPM value is then compared against the settings for shift1, shift2 and shift3. ECU (LO). The ignition coil signal is filtered using one or two 47nF capacitors (LK1 adds the second capacitor) and then AC-coupled via a 2.2mF capacitor to the next stage comprising a 100kW resistor and 16V zener diode clamp (ZD2). Diodes D5 and D6 clamp the signal between +5.6V and -0.6V before it is fed to the RB0 input at pin 6 of IC1. The inputs that connect to the BCD switch and to the Select (S1) and Set (S2) switches are normally pulled to +5V via internal resistors. When the respective switch is closed, its input is pulled low. Switches S1 and S2 are continuously monitored by IC1. Circuit description Engine selection The full circuit is shown in Fig.3. It is based on IC1, a PIC16F88-I/P microcontroller which monitors the RPM signal. It then makes the RPM calculations and comparisons with the set shift and limit levels and drives the associated LEDs and limiting circuitry. IC1 operates at 8MHz and is powered from a 5V supply derived from 3-terminal regulator REG1. Two RPM signal input options are provided: either from the ignition coil negative terminal (HI) via a 22kW resistor or the nominal 5V signal from the BCD switch S3 selects the engine type. This has four switches (at RB4, RB3, RB1 & RB2) and provides 16 possible combinations, ranging from all switches open to all closed. The settings for S3 are checked by IC1 when it is first powered up; this sets the required engine type for RPM calculations. VR1 provides the RPM values for the shift and limit settings. The series 30kW and 10kW resistors connected to the trimpot’s wiper reduce the maximum voltage at TP1 to 1.25V. 68  Silicon Chip In practice, VR1 is adjusted to provide the desired RPM voltage at TP1 and 1V is equivalent to 10,000 RPM. So to set the RPM to 5500 RPM, VR1 is adjusted so that the voltage at TP1 is 0.55V. Trimpot VR2 sets the hysteresis range for each shift and limit setting. A 5V setting at TP2 provides 500-RPM hysteresis and 1V gives 100-RPM hysteresis. Trimpot VR3 sets the ambient light threshold for dimming the LEDs. The LEDs are bright enough to be easily seen in daytime driving and therefore need to be dimmed for night-time driving. The ambient light is monitored by a Light Dependent Resistor (LDR1) and it is connected in series with a 10kW resistor and trimpot VR3 to provide a voltage at IC1’s AN5 input. The 10mF capacitor at the AN5 input averages out changes in ambient light. This prevents the display rapidly changing in brightness if passing along a street lit area at night. Dimming is achieved by driving the LEDs with a duty cycle that can be varied from 1.56% through to 100% (full brightness) in 63 steps. Microcontroller outputs Apart from the three shift LED outputs at pins 15, 16 & 17, there are siliconchip.com.au siliconchip.com.au February 2008  69 Fig.3: the circuit is based on PIC16F88-I/P microcontroller IC1. This stores the shift and limit settings and compares these against the incoming RPM signal that’s fed to its RB0 input at pin 6. IC1 then drives shift LEDs1-3 at its RA6, RA7 & RA0 outputs accordingly. The RA1 output drives the soft limiting circuitry (Q1, Q3, Q5 & Q5), while RA2 drives relay RLY1 via Q2 to provide the hard limiting option. Fig.4: install the parts on the PC board as shown on this parts layout diagram. You can either mount LEDs1-4 & the LDR on the main board as shown, or you can mount these parts on a separate display PC board (shown at bottom right). The two boards are connected together via a 16-way ribbon cable fitted with IDC line plugs. two rev limiting outputs at pins 18 & 1 (RA1 & RA2). Pin 1 (RA2) drives transistor Q2 and this in turn drives an external relay (RLY1) for the hard limiting function. Diode D2 clamps any back-EMF spikes produced by the relay’s coil when the transistor is switched off. Pin 18 (RA1) drives transistor Q1 and this then drives the gates of Pchannel Mosfets Q4 & Q5 for the softlimiting function. Q4 & Q5 control the positive supply to the motor’s fuel injectors and this can be progressively reduced by varying the duty cycle of the pulse width modulation drive. In operation, P-channel Mosfets Q4 & Q5 provide “high side” switching of the injector supply rail. Normally, the RA1 output at pin is set high to turn on transistors Q1, Q4 & Q5 so that the injectors are fully powered. Above the set RPM limit, IC1’s RA1 output (pin 18) will switch Mosfets Q4 & Q5 with a duty cycle which is reduced gradually until there is no injector drive once the motor is over the set limit. The pulse frequency to the injectors is 30.5Hz. Mosfets Q4 & Q5 are driven in the following way: when Q1 is switched off, the base of transistor Q3 is pulled high via a 2.2kW resistor to +12V. This turns on Q3 and so its emitter pulls the gates of Q4 & Q5 towards the +12V supply and switches them off. However, when Q1 is switched on, Q3 is switched off and its emitter is pulled down to 0V via diode D3. This pulls the gates of Q4 & Q5 low and switches them on. Diode D4 is included to protect Q4 & Q5 from the back-EMF spikes produced by the injectors when they turn off. Power supply Power for the circuit is derived from the vehicle’s +12V rail via diode D1. This provides protection if the supply Table 2: Capacitor Codes Value 47nF 10nF mF Code IEC Code EIA Code 0.047mF 47n 473 0.01mF 10n 103 Table 1: Resistor Colour Codes o o o o o o o o o o No. 1 1 1 5 2 2 5 2 1 70  Silicon Chip Value 100kW 30kW 22kW 10kW 2.2kW 1kW 220W 100W 47W 1W 5% 4-Band Code (1%) brown black yellow brown orange black orange brown red red orange brown brown black orange brown red red red brown brown black red brown red red brown brown brown black brown brown yellow violet black gold 5-Band Code (1%) brown black black orange brown orange black black red brown red red black red brown brown black black red brown red red black brown brown brown black black brown brown red red black black brown brown black black black brown not applicable siliconchip.com.au Fig.5: the mounting details for REG1 & Mosfets Q4 & Q5. Each device is electrically isolated from the case using an insulating washer and bush (see photo). Make sure that all polarised parts are correctly oriented when installing them on the board. The locating slot in the IDC header goes towards the bottom edge. Don’t install the IC until the supply has been tested. is connected the wrong way around. A 16V zener diode (ZD1) clamps any spike voltages which may occur on the battery supply and further filtering is provided by the 100mF capacitor for the supply to REG1, a 7805 5V regulator. The 5V rail from REG1 is used to power IC1. Construction The Shift Light Indicator is built on a PC board coded 05102081 (101 x 81mm), while a separate display board coded 05102082 (42 x 19mm) carries the display LEDs. Alternatively, the LEDs can be mounted on the main board. If you do elect to use the separate display board, it’s connected back to the main board via a 16-way ribbon cable fitted with IDC headers (Fig.6). As usual, begin construction by checking the PC board for any defects such as shorted tracks and breaks in the copper. That done, check that the hole sizes are correct. The holes for the four corner mounting screws need to be 3mm in diameter, while the holes for the screw terminal blocks need to be 1.2mm. Check also that the PC board fits into the box. If it doesn’t fit, use a small file to round the corners until is does. Fig.4 shows the parts layout on siliconchip.com.au the PC board. Start the assembly by installing the wire links, followed by the resistors. Table 1 shows the resistor colour codes but you should also check each one using a digital multimeter before installing, as some colours can be hard to read. Next, install the PC stakes for test points TP GND, TP1 & TP2. That done, install the 2-way header for LK1. Follow these with the diodes and zener diodes, taking care to install each with the correct orientation. Once these parts are in, install a socket for IC1 with its notched end towards Q2. Don’t install the IC yet – that step comes later. The capacitors can go in next, again taking care to ensure that the electrolytics are correctly oriented. That DISPLAY BOARD CONNECTOR 16-WAY IDC CABLE done, install transistors Q1-Q5 and regulator REG1. Note that REG1, Q4 & Q5 mount with their leads protruding through the bottom of the PC board by about 1mm. This will leave sufficient lead length to allow the devices to be later fastened to the side of the box. Now install trimpots VR1-VR3 and the BCD switch. The correct orientation for S3 is with its corner dot to the lower left – see Fig.4. Switches S1 & S2 can then be inserted. These two switches will only fit on the PC board with the correct orientation. The next step is to mount the two 6.8mm PC spade terminals, the 16way IDC cable socket and the screw terminal blocks. Note that the 4-way terminal block consists of two 2-way blocks which are joined by sliding their moulded dovetails together. Display board assembly Fig.4 also shows the display board assembly. It should only take a few minutes to assemble. There are a couple of options here MAIN BOARD CONNECTOR GROMMET PIN 1 LOCATING SPIGOT SIDE OF BOX LOCATING SPIGOT Fig.6: here’s how to make up the IDC cable that connects the display board to the main board. The header plugs can be clamped together using a small vice. Note the positions of the locating spigots on the plugs. February 2008  71 Features & Specifications Features • Three independent shift indicator LEDs • One RPM limit LED • Adjustable hysteresis for each shift setting and at the limit • Relay switching of injectors at limit (hard limiting) • Alternative soft limiting using pulse width modulation (PWM) • Suits most petrol engines, including asymmetrical cylinder types • Automatic dimming of shift LEDs & adjustable minimum brightness • Easy adjustment of shift and RPM limit settings • Easy engine selection – suits all engine types from 1-12 cylinders • Easy adjustment of soft limiting effect Specifications RPM accuracy: typically <2% at 25°C with a 5.0V supply. Maximum shift & limit settings: 12,500 RPM for 1 to 12-cylinder 4-stroke engines (1 to 6-cylinder 2-stroke). Shift & limit RPM adjustment: 0 to >12,500 RPM in 25 RPM steps. Adjustment for RPM using VR1: 1V = 10,000 RPM, 0.5V = 5000 RPM (5.0V supply). Hysteresis adjustment: 0-500 RPM in 2-RPM steps Adjustment for hysteresis using VR2: 1V = 100 RPM, 5V = 500 RPM (5.0V supply). Shift and limiting response: RPM dependent (see Table 3). PWM limiting response is slowed using effects. Soft limiting PWM: 100% to 0% with a maximum of 250 steps over the hysteresis RPM range at a 30.5Hz rate. Soft limiting effects: PWM update after 1-16 PWM cycles, RPM measurement averaging over 1-64 RPM values. Dimming of shift LEDs: full range of 63 dimming steps from 1.5625% to 100% using PWM at 122Hz. The 0% PWM is not included. Minimum dimming can be adjusted to any one of the 63 settings. when it comes to mounting the LEDs and the LDR. One option is to bend the LED leads at right angles about 8mm from their bodies and install them so that they sit at right angles to the PC board as shown in the photo. Similarly, the LDR’s leads can be bent at right angles about 11mm from its body before installing it on the board. A 7mm-wide cardboard spacer can be used to ensure that these parts all sit the same distance above the board. Alternatively, you can push the parts right down onto the board so that the leads touch the board surface. Another option is to mount the LEDs and the LDR on the back of the 72  Silicon Chip PC board. It all depends on how you intend to ultimately mount the display board on the dashboard. Which ever option you choose though, be sure to install each LED with the correct orientation – the anode lead is always the longer of the two. The LDR can go in either way around. Once these parts are in, install the IDC socket. The other option is to install the LEDs and the LDR on the main PC board. In that case, you will have to later drill matching holes in the side of the case. Final assembly A metal diecast case measuring 111 x 60 x 54mm is used to house the main board. This makes for a rugged assembly and provides heatsinking for regulator REG1 and the two power Mosfets (Q4 & Q5). The first step here is to drill the four mounting holes in the base for the PC board. That done, fit four 10mm spacers to the case, then mount the board in position and secure it using M3 x 6mm screws and nuts. Having secured the board, bend the leads for REG1, Q4 and Q5 so that their metal tabs sit flat against the sides of the case. Carefully mark out their tab mounting holes, then remove the PC board and drill these holes to 3mm. Be sure to de-burr each hole using an oversize drill, to give a clean, flat surface (this is important to prevent punch-through of the insulating washers when the devices are secured to the case). In addition, you will have to drill three 9.5mm holes in the side of the case to provide external wiring access. These holes should be opposite (and slightly above) the 2-way and 4-way terminal blocks and the IDC header. Use a small pilot drill to start these holes, then ream them to size and de-burr them before fitting the rubber grommets. Note: the hole opposite the IDC header is not required if the LEDs and LDR are mounted on the main board. You will, however, have to drill five holes to accept the LED bodies and to allow light through to the LDR. The PC board can now be reinstalled and REG1, Q4 and Q5 secured to the sides of the case. Note that their metal tabs must be electrically isolated from the case using TO-220 insulating washers and mounting bushes – see Fig.5. Each device is secured using an M3 x 10mm screw and nut. Once these devices have been secured, use a multimeter to confirm that their metal tabs are indeed isolated from the case. The IDC cable can now be installed. This is done by first rolling up the cable and feeding it through the hole opposite the IDC socket. The IDC plug can then be attached, making sure that the orientation is correct (see Fig.6). Use a small vice to clamp the header plugs together to secure the cable. Testing the PC board The first step in the test procedure is to apply power to the +12V & 0V siliconchip.com.au terminals on the 4-way terminal block. That done, check the voltage between pins 14 & 5 on the IC socket. This should be close to 5V (a range of 4.8V and 5.2V is acceptable). If the voltage is below 4.8V, check for a short on the PC board. If there is no voltage, check that diode D1 is the right way around. Assuming that everything is correct, switch off and install IC1 in its socket. It must be installed with its notched end towards transistor Q2, Next, apply power and adjust trimpot VR3 fully clockwise. Now press switch S1 and check that LED1 lights. Repeated pressings should now cause LED2, LED3 and LED4 to light in sequence, with only one LED on at a time. These correspond to the settings mode for Shift1, Shift2, Shift3 and Limit respectively. If S1 is now pressed again, LED 4 (Limit) should remain on while LEDs1-3 should light up in sequence at a relatively fast rate. This is the soft limiting setting mode for the rev limiting feature. Pressing S1 yet again should turn on just LED1, LED2 & LED3. This is the selection for setting the minimum dimming level. Finally, pressing S1 again should switch all the LEDs off. This returns the unit to its normal mode, whereby each LED lights when the incoming RPM signal reaches its respective threshold. Threshold adjustments As noted already, trimpots VR1 & VR2 are used to set the Shift and Limit thresholds and hysteresis values. The first step it to set these values for Shift1. The procedure is as follows: Step 1: press switch S1 so that LED1 lights. Step 2: attach a multimeter between TP1 & TP GND and adjust VR1 to set the desired RPM threshold. Note that the voltage on TP1 is directly related to the RPM setting, where 1V represents 10,000 RPM. To set a 4000 RPM threshold, for example, adjust VR1 for a reading of 0.4V (400mV). Note also that, due to trimpot resolution, you may not be able to adjust the voltage to better than within 5mV (equivalent to 50 RPM) of the desired value. Step 3: connect a multimeter between TP2 & TP GND. Step 4: adjust VR2 to set the RPM siliconchip.com.au The PC board is mounted inside the case on 10mm spacers and secured using M3 x 6mm screws. REG1, Q4 & Q5 are then bolted to the case – see Fig.5. Note that the wiring to the fuel injectors is not required if you opt for hard limiting. hysteresis value. This can be adjusted from 0-500 RPM. Note that 5V at TP2 sets the hysteresis to 500 RPM, 4V gives 400 RPM and so on. Step 5: press Set switch S2 to program the RPM threshold and hysteresis adjustments for Shift1 into IC1. LED1 will now flash five times to indicate that these settings have been saved. Note: if you require the highest possible accuracy, you will have to scale the adjustment voltages to compensate for REG’s output (ie, if this is not exactly +5V). In practice, it’s just a matter of multiplying the threshold RPM required by the measured supply voltage and dividing the result by 5V. For example, let’s say that you want to set the RPM threshold to 4000 RPM and that the supply voltage is 4.95V. In that case, the calculation is 4000 x 4.95V/5V or 3960. So to adjust for 4000 RPM when the supply is 4.95V, you must set VR1 to give 0.396V at TP1. Step 6: press S1 so that LED2 lights and repeat the above steps (through to Step 5) to set the threshold and hysteresis values for Shift2. Repeat this procedure to set the values for Shift3, making sure each time that the correct LED is selected. Don’t forget to press S2 to save the changes each time you adjust VR1 & VR2 for each Shift setting. This must be done before moving on to the next Shift light, otherwise the settings will not be saved. Rev limit adjustments Now for the rev limit adjustments. Just follow these steps: Step 1: press S1 after the Shift3 settings have been saved. This turns LED4 (Limit) on, while all the other LEDs are off. Step 2: monitor the voltage at TP1 and adjust VR1 to set the rev limit. As before, 1V is equivalent to 10,000 RPM so to set a limit of 6000 RPM, for example, set VR1 for a reading of 0.6V. Step 3: monitor TP2 and adjust VR2 to set the rev limit hysteresis. In this case, 1V is equivalent to 100 RPM. If you intend using PWM limiting so that the engine power drops off gradually, use an initial value of 500 RPM (5V at TP2). Alternatively, if you intend using relay limiting, set the value to 200 RPM (2V at TP2). Step 4: press S2 to save these settings. Step 5: press S1 to bring up the soft February 2008  73 RLY1 (a) STANDARD INJECTOR WIRING INJECTOR 4 INJECTOR 3 INJECTOR 2 INJECTOR 1 INJECTOR 4 INJECTOR 3 INJECTOR 2 INJECTOR 1 ECU ECU (b) WIRING FOR HARD LIMITING 87(NO) B RLY1 C(30) SHIFT INDICATOR & REV LIMITER 87a(NC) INJECTOR 4 C(30) 87a(NC) EXISTING +12V INJECTOR SUPPLY RAIL A NEW INJECTOR SUPPLY RAIL INJECTOR 3 87(NO) INJECTOR 2 EXISTING +12V INJECTOR SUPPLY RAIL INJECTOR 1 EXISTING +12V INJECTOR SUPPLY RAIL ECU (c) WIRING FOR SOFT LIMITING Fig.7: these diagrams shows the standard fuel injector setup (a) plus the modifications required to wire in the limiter circuit for hard limiting (b) or soft limiting (c). Be sure to use a relay with 30A contacts, as specified in the parts list. Note that the relay (RLY1) is used in both the hard limiting and soft limiting circuits – see panel. limiting adjustment mode – ie, LED4 lit and LEDs1-3 lighting in sequence. Trimpot VR1 now adjusts the number of RPM calculations that are used in averaging the RPM reading while VR2 adjusts the rate at which the PWM (pulse width modulation) that provides the soft limiting changes. Setting VR1 fully clockwise gives an average of 64 RPM calculations, while setting VR2 fully clockwise gives 16 PWM cycles before changes occur. Conversely, fully anticlockwise settings for VR1 and VR2 give no averaging and a PWM that can change with each cycle. Setting both VR1 & VR2 to mid-way would provide a suitable soft limiting effect for most engines. However, if the soft limiting subsequently proves to be too soft, so that the engine RPM overshoots the desired limit by a large margin, then the trimpots should be adjusted further anticlockwise. Note that VR1 has an effect on both the soft limiting smoothness and the response time when it comes to limiting the engine RPM. VR2 only affects the RPM limiting response speed. Step 6: press S2 to save the soft limiting settings. Dimming adjustments Pressing S1 again brings up the Surround the base & leads of diode D4 with neutral cure silicone This view shows how power Mosfets Q4 & Q5 are bolted to the case and their tabs isolated using insulating washers and bushes. REG1 mounts in similar fashion – see also Fig.5. Note that diode D4’s leads should be surrounded with neutral-cure silicone, to prevent them from vibrating and breaking. 74  Silicon Chip dimming adjustment mode (LEDs1-3 all lit, LED 4 off). It’s now just a matter of covering the LDR sufficiently (both front and back) to bring the LED brightness down to the minimum level you require and then pressing the Set switch (S2) to save the setting. The three LEDs will then flash five times to indicate that this has now been stored. Note that the above procedure is best carried out in a room with a low ambient light level (but not dark). That done, adjust VR3 to set the ambient light level threshold at which dimming begins (this may take some trial and error). By the way, changing the 10mF capacitor at pin 12 of IC1 to 1mF will increase the rate at which the LEDs dim or become brighter in response to ambient light changes. Installation The unit is relatively straightforward to install and requires only a limited amount of external wiring. This involves wiring for the +12V and ground (0V) connections, the rev signal input and the connections to the fuel injectors. The +12V supply can be obtained from the fusebox and must be switched on (or off) by the ignition. Note, however, that this supply rail must remain on when the engine is being cranked (ie, when the starter motor is running). The 0V rail can be connected to vehicle siliconchip.com.au Parts List 1 main PC board, code 05102081, 101 x 81mm 1 display PC board coded 05102082, 42 x 19mm 1 diecast case, 111 x 60 x 54mm 1 SPDT 30A horn relay 1 relay base to suit horn relay (optional) 3 2-way PC-mount screw terminals (5.08mm spacing) 1 PC-mount 0-F BCD DIL switch (S3) 2 SPST micro tactile switches (S1,S2) 2 16-way IDC PC-mount headers 2 16-way IDC line plugs 2 6.8mm PC-mount spade terminals 2 6.8mm insulated spade crimp connectors 3 rubber grommets for 6mm cable diameter 3 TO-220 silicone insulating washers 3 3mm insulating bushes 4 M3 x 10mm tapped Nylon standoffs 8 M3 x 6mm screws 3 M3 x 10mm screws 3 M3 nuts chassis. These supply connections can be run using medium-duty automotive hook-up wire. The rev signal can be from derived from the coil’s negative terminal and this wire connects to the HI input. Alternatively, in a multi-coil car, you can use the ECU tachometer signal and this should go to the LO input. Injector wiring Fig.7(a) shows the basic set-up for standard injector wiring. Note that the engine management system (ECU) switches the negative side of the fuel injectors. The first step is to disconnect the injectors from their existing common positive supply rail. After that, it depends on whether you are opting for hard limiting or soft limiting. If you are opting for hard limiting, it’s simply a matter of wiring in the relay as shown in Fig.7(b). This involves first connecting the vehicle’s existing +12V injector supply rail to the relay’s common (C) contact. The normally siliconchip.com.au 1 2-way header with 2.54mm spacing (LK1) 1 jumper plug (for LK1) 3 PC stakes 1 1m length of 16-way IDC cable 1 160mm length of 0.8mm tinned copper wire 1 1m length of figure-8 20A automotive wire 1 1m length of red medium-duty automotive wire 1 1m length of black mediumduty automotive wire Trimpots & LDR 2 1kW horizontal mount trimpots (VR1,VR2) 1 500W horizontal mount trimpot (VR3) 1 LDR (50kW light & 10MW dark resistance) (LDR1) Semiconductors 1 PIC16F88-I/P microcontroller programmed with 0510208A. hex (IC1) 1 7805 3-terminal regulator (REG1) 2 IRF9540 P-channel Mosfets (Q4,Q5) 3 BC337 NPN transistors (Q1-Q3) 2 1N4004 diodes (D1,D2) 1 UF4003 ultrafast diode (D3) 1 BY229 fast diode (D4) 2 1N4148 diodes (D5,D6) 2 16V 1W zener diodes (ZD1,ZD2) 2 18V 1W zener diodes (ZD3,ZD4) 1 5mm high-intensity green LED (LED1) 1 5mm high-intensity yellow LED (LED2) 2 5mm high-intensity red LEDs (LED3,LED4) Capacitors 3 100mF 16V PC electrolytic 2 10mF 16V PC electrolytic 1 2.2mF 63V PC electrolytic 2 47nF MKT polyester 1 10nF MKT polyester Resistors (0.25W, 1%) 1 100kW 2 1kW 1 30kW 5 220W 1 22kW 0.5W 2 100W 5 10kW 1 47W 1W 2 2.2kW Why Use The Relay With Soft Limiting? Strictly speaking, if you elect to use soft rev limiting, the relay shown in Fig.7(c) is optional. However, we still recommend wiring it into circuit for a couple of reasons. First, by using the relay as shown, its NC contacts take the load off the soft limiting Mosfets (Q4 & Q5) during normal engine operation. However, if the rev limit is reached, the relay quickly opens and the Mosfets then take over to provide the soft limiting function – ie, they pulse width modulate the new injector supply rail. Second, the relay’s contacts ensure that the injectors are still supplied with power during normal running if the Mosfets become faulty or if a fault develops in the unit which switches them off. For this reason, we strongly recommend that you include the relay as shown in Fig.7(c) – it’s a worthwhile safety and reliability feature. closed (NC) contact is then connected to the positive injector terminals. Note that all wiring to the relay contacts and to the injectors should be run using 20A automotive cable. Note also that, for hard limiting, no connections are made to points A & B on the circuit board. Alternatively, if you are opting for soft limiting, then you need to wire the injectors as shown in Fig.7(c). In this case, the vehicle’s existing injector positive supply rail is connected to point A on the main PC board. Point B on the circuit board then becomes the new injector positive supply rail. February 2008  75 Table 3: BCD Switch Settings & Details For Various Engine Types Frequency/ 1000 RPM Shift light Response <at> 1000 RPM Shift light Response <at> 2000 RPM Between each pulse 8.33Hz 120ms 60ms Between each pulse 16.66Hz 60ms 30ms Between each pulse 25Hz 40ms 20ms Between each pulse 33.33Hz 30ms 15ms 2.5 Between each pulse 41.66Hz 24ms 12ms 50Hz 20ms 10ms BCD Switch Setting (S3) Cylinders (4-stroke) Cylinders (2-stroke) Pulses per RPM RPM Counter 1 1 – 0.5 2 2 1 1 3 3 – 1.5 4 4 2 2 5 5 – 6 6 3 3 Between each fourth pulse 8 8 4 4 Between each fourth pulse 66.66Hz 15ms 7.5ms 9 Asymmetric 3-cylinder – 3 over 2 RPM Between each fourth pulse 25Hz 80ms 40ms A 10 5 5 Between each fourth pulse 83.33Hz 12ms 6ms B Asymmetric 2-cylinder – 2 over 2 RPM Between each fourth pulse 16.66Hz 120ms 60ms C 12 6 6 Between each fourth pulse 100Hz 10ms 5ms The relay is also wired into circuit as before. Once again, be sure to use 20A automotive cable for the wiring to the injectors, the relay contacts and to points A & B on the PC board. Note that this wiring is run to the main board by feeding it through the adjacent rubber grommet and terminating it with spade crimp connectors. These connectors are then plugged into the A & B terminals. Make sure that the crimp connections are nice and tight to ensure reliability and be sure to plug each into its correct terminal. A ratchet-driving crimping tool is a necessity here. It’s vital that all wiring be installed in a professional manner, to ensure reliability. That means using proper automotive connectors to terminate the wiring and securing the wiring with tape and cable ties. Testing Once the wiring is complete, set the BCD switch to the number that suits your engine – see Table 3. That done, start the engine and rev it to check that the shift & limit LEDs light at their correct RPM values. If Determining The Shift Points How do you determine the best shift points to program into the Shift Indicator & Rev Limiter? In most cases, it’s just a matter of driving the car and noting down a sensible RPM value for each gear change. The values can then be programmed into the unit, after which it’s simply a matter of monitoring the LEDs to pick the gear-change points. Alternatively, as mentioned in the text, you could set the three LEDs to give a ‘ready’, ‘set’ and ‘go’ indication for each gear change. The rev limit can simply be set to just under the tacho’s redline value. Note, however, that many modern cars include rev limiting as part of their engine management system. In that case, you won’t need the rev limiting feature provided by this unit and it’s just a matter of leaving out the wiring between this unit and the fuel injectors (you can also leave out the relay, power Mosfets Q4 & Q5 and transistors Q1-Q3). If you are modifying a car for racetrack use, then the shift points would be set much more aggressively – typically at those points that provide maximum acceleration. In some cases, you might want to set the shift points at close to engine redline. In other cases, it may be a matter of picking the maximum engine power points. 76  Silicon Chip you haven’t yet programmed the unit, the initial settings are 1000 RPM for shift1, 2000 RPM for shift2, 3000 RPM for shift 3 and 4000 RPM for the limit. The hysteresis is 200 RPM for shift1 and 500 RPM for the other thresholds. If the shift points are incorrect and you are using the HI input, try installing link LK1 to change the input filtering. Alternatively, if you are using the LO input, LK1 has no effect and no adjustments to the input filtering should be necessary. If the LEDs do not light at all, check that the RPM input signal is correctly connected. Peak hold injectors Finally, note that the soft limiting option is not suitable for injectors that operate with a so-called peak hold drive. This is where an initial high current is used to close the injector but then the current is reduced by rapidly switching the injector signal on and off (this keeps the injector open but with reduced power to the injector solenoid). Note, however, that you can use the hard limiting option, provided that the relay contacts can handle the peak currents that drive this type of injector. How do you know whether you have peak hold injectors? They will typically have a solenoid coil resistance of less than 1W (normal injectors have SC a resistance of 4-5W). siliconchip.com.au