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Chapter 15 Delta Throttle Timer A really tricky way of turning devices on and off – it measures how enthusiastically you’re driving! S O WHAT THE HELL is a “Delta Throttle Timer”? It doesn’t sound like the sort of thing that’s very interesting, does it? But if you think that, you’re wrong, wrong, wrong. What this device does is activate a timer Main Features •  Has a 0-5V signal input •  Powers a relay when a specific rate of voltage change occurs •  Adjustable rate threshold •  Adjustable timer from 0.1s to 110 seconds •  Double-pole double-throw relay with 5A contacts •  Selectable rising or falling voltage rate switching •  Power-up delay to prevent false triggering at ignition-on 86 PERFORMANCE ELECTRONICS FOR CARS and relay when you’re accelerating (or alternatively, decelerating) hard. And here’s the tricky bit – it works this out by actually measuring how quickly you’re moving the accelerator pedal! Say you’re on the way home and the road passes through a section of winding country road. You weren’t really thinking of driving hard but the inspiration of those bends suddenly hits you – and your foot goes down fast. You wind out the engine in second gear, flick the lever across to third and then flatten the throttle again. A corner approaches and you lift off, turn in and then right at the apex, get back hard on the power. The Delta Throttle Timer (DTT) has all the time been watching the voltage coming from the throttle position sensor. When it recognises how fast you’re pushing down on the throttle, it activates a timer which in turn controls a relay. If that relay is connected to (say) an intercooler water spray, you’ll be cooling the core even before the car comes up on boost! Set the timer for an interval of 30 seconds and that’s how long the spray will stay on for but you can repeatedly extend the time if you push down fast on the throttle again before the relay times out. Of course, when you go back to gentle driving, the spray will then turn off. Other Uses The DTT is also the perfect way of triggering engine and transmission modifications. For example, you could make it so that when you drive with fast throttle movements the turbo boost increases. Or you can use the DTT to automatically switch the transmission’s Power/ Economy button to Power mode when you’re really going for it. The more you think about it, the greater the possibilities. Now you’ve siliconchip.com.au Fig.1: this shows where each of the components is placed on the main PC board. Use this diagram, the photos of the completed board and the parts list to help you assemble it correctly. In particular, note the orientation of VR1 & VR2. got an excuse to blip the throttle at the lights before you take someone on (just kidding)! But wait, there’s more! Because the DTT can be alternatively configured to also measure quick throttle lifts, you can also use the device to control an electric blow-off valve. In that application, the timer would be set for a very short period – say one second – so that whenever you quickly lift the throttle (eg, for a gear-change), the blow-off valve will open. However, at idle, the valve will stay shut, avoiding those problems where intake air can be drawn in through the open valve. Finally, another great application is Suggested Uses For This Project When configured to measure quick downwards throttle movements: •  Switching engine management and auto transmission control modifications in and out •  Automatic switching of the Power/Economy auto transmission button •  Automatic turbo boost increase with hard driving •  Intercooler water spray and/or intercooler fan control When configured to measure quick throttle lifts: •  Electronic blow-off valve control •  Early brake light illumination (QuickBrake) When constructed, your circuit board should look like this. Be sure to install all the polarised components with the correct orientation; ie, the diodes, ICs, LED, transistors, voltage regulator and electrolytic capacitors. siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 87 How It Works Fig.2 shows the circuit which is based on four op amps (in IC1 & IC2) and a 7555 timer. In effect, the circuit is designed to detect the rapid change of voltage from the throttle position sensor and then close a relay for a brief time. The relay then switches on for a pre-determined time and then drops out. OK, let’s look at the circuit in more detail. The DC voltage from the throttle position sensor is fed to a low-pass filter consisting of a 1MΩ resistor and 100nF capacitor and then to op amp IC1a which is connected as a unity gain buffer. From there, it goes to a differentiator consisting of a 100nF capacitor, trimpot VR1 and a 100kΩ resistor. A differentiator can be thought of as a high pass filter – it lets rapidly changing signals through but slowly changing signals are blocked. Putting it another way, if the rate of change of the signal is greater (ie, faster) than the differentiator time constant (RC), the signal will pass through to op amp IC1b, which is another unity gain buffer. IC2a is also wired as a unity gain buffer and it inverts the output from IC1b. Link LK1 then selects either the output of IC1b or IC2a, so that the circuit can trigger on either a falling (H/L) or rising (L/H) input signal. The selected signal is fed to IC2b which is connected as a Schmitt trigger stage. IC2b’s output is fed (via a 1kΩ resistor) to the pin 2 trigger input of IC3, a 7555 timer. When IC2b briefly pulls pin 2 of IC3 low (eg, if there is a sudden increase or reduction in the throttle sensor signal), IC3’s pin 3 output immediately goes high, turning on transistor Q1 and Relay1. At the same time, IC2b’s brief negative pulse turns on transistor Q2 which pulls the negative side of a 100µF capacitor to 0V and this fully charges this capacitor to 8V. From this point, the 100µF capacitor discharges via trimpot VR2 and the series 1kΩ resistor. This means that the negative side of the 100µF capacitor rises until it gets to about +5.3V, at which point pin 3 goes low and transistor Q1 and the relay are switched off. IC3’s timing period can be set from around 100ms up to 110 seconds, using VR2. Diode D2 is connected across the relay coil to quench the spike voltages that are generated each time transistor Q1 turns off. Q1 also drives LED1, via a 1.8kΩ series resistor, and this lights when ever the relay is energised. Power-Up Delay Pin 4 of the 7555 (IC3) is used to provide a power-up delay. When the car is first started, we don’t want the circuit responding to any unpredictable changes in signal from the throttle sensor, etc; instead, we With the Delta Throttle Switch, it’s possible to automatically trigger devices like an intercooler water spray as soon as you start driving hard – even before the car is on boost! 88 PERFORMANCE ELECTRONICS FOR CARS want all circuit operating conditions to have stabilised before it starts working. Therefore, pin 4 of IC3 is connected to a network comprising a 470µF capacitor, diode D4, and 39kΩ and 220kΩ resistors. Initially, the 470µF capacitor is discharged and so pin 4 is low, effectively disabling IC3 so it cannot respond to any unwanted trigger signals to its pin 2. IC3 is enabled (ie, begins to operate) when the 470µF capacitor charges to around +0.7V via the 220kΩ pull-up resistor. This is after about two seconds. The 39kΩ resistor prevents the 470µF capacitor from charging above 1.2V and this allows it to discharge quickly via diode D4 when power is removed from circuit (ie, when the engine is stopped). This is important so that the circuit is properly disabled if the engine is immediately restarted. Power for the circuit comes from the switched +12V ignition supply via diode D1, which gives reverse connection protection. The 10Ω resistor, 100µF capacitor and zener diode ZD1 provide transient protection for REG1, a 7808 8V regulator. All the circuitry is powered from REG1, with the exception of Q1, the relay and LED1. Fig.2: the circuit monitors the car’s throttle position sensor and if a rapid transition occurs, the 7555 timer IC is enabled. This in turn briefly activates the relay. to use quick throttle lifts to activate the brake lights. This gives following drivers up to 250ms earlier warning that you’re about to apply the brakes. That amounts to about seven metres at 100km/h and could be all the difference between a safe stop or a severe rear-end shunt! This application of the Delta Throttle Timer was featured in an article entitled “QuickBrake” in the March 2004 issue of SILICON CHIP and in issue 282 of “AutoSpeed”. The DTT is easy to build, and very easy to connect and set-up. Apart from the device that you are controlling, only three connections are needed to the car’s wiring – ignition-switched siliconchip.com.au +12V, earth and the throttle position sensor. Construction When assembling the PC board, make sure that you insert the polarised components the correct way around (the diodes, ICs, LED, transistors, voltage regulator and electrolytic capacitors are the easiest to make mistakes with). During construction, closely look at the photos, overlay diagram and parts list to avoid making mistakes. The component overlay diagram is shown in Fig.1. Install the resistors first, checking the values with your multimeter as you install each one. siliconchip.com.au RESISTOR COLOUR CODES Value 4-Band Code (1%) 5-Band Code (1%) 1MΩ brown black green brown brown black black yellow brown 220kΩ red red yellow brown red red black orange brown 100kΩ brown black yellow brown brown black black orange brown 39kΩ orange white orange brown orange white black red brown 11kΩ brown brown orange brown brown brown black red brown 10kΩ brown black orange brown brown black black red brown 1.8kΩ brown grey red brown brown grey black brown brown 1kΩ brown black red brown brown black black brown brown 150Ω brown green brown brown brown green black black brown 10Ω brown black black brown brown black black gold brown PERFORMANCE ELECTRONICS FOR CARS 89 Parts List 1 PC board coded 05car071 or 05103041, 105 x 60mm 5 PC-mount 2-way screw terminals with 5mm pin spacing 1 12V PC-mount DPDT 5A relay (Relay1) 1 3-way header with 2.54mm spacing 1 jumper shunt with 2.54mm spacing 1 50mm length of 0.8mm tinned copper wire 2 1MΩ horizontal trimpots (VR1,VR2) Semiconductors 2 LM358 dual op amps (IC1,IC2) 1 7555 CMOS 555 timer (IC3) 1 7808 3-terminal regulator (REG1) 1 BC337 NPN transistor (Q1) 1 BC327 PNP transistor (Q2) 1 5mm red LED (LED1) 2 16V 1W zener diodes (ZD1,ZD2)) 2 1N4004 1A diodes (D1,D2) 2 1N4148 switching diodes (D3,D4) Capacitors 1 470µF 16V electrolytic 5 100µF 16V PC electrolytic 4 10µF 16V PC electrolytic 3 100nF MKT polyester (code 104 or 100n) Resistors (0.25W, 1%) 2 1MΩ 1 220kΩ 1 100kΩ 1 39kΩ 1 11kΩ 5 10kΩ 1 1.8kΩ 4 1kΩ 1 150Ω 1 10Ω Use 0.8mm tinned copper wire for the two wire links. The relay and the screw terminal strips can be installed last. Note that there is a trap in the installation of the two trimpots. They can go in either way but they must be installed as shown in the diagram, with the adjustment screw closest to IC2 and IC3 respectively. If you install the trimpots incorrectly, the initial adjustment instruction that we give in the set-up procedure will be wrong. Testing & Fitting This project is best tested in the car, because you can do so without actually having to drive anywhere. The first step is to measure the 90 PERFORMANCE ELECTRONICS FOR CARS The Delta Throttle Timer monitors the output of the throttle position sensor (circled). When it detects that the driver is moving the throttle quickly, the relay trips, allowing a range of devices to be triggered according to how enthusiastically you’re driving. It’s Been Done Before While the Delta Throttle Timer is a new concept in aftermarket modification, a similar concept is used in nearly all recent factory cars. The speed with which the throttle is moved helps determine the rate of transient ignition timing change and the injection of fuel (the latter is the accelerator pump, if you like). In cars with sophisticated electronic transmission control, gear down-changes are also determined by how fast the throttle is moved as much as it is by how far the throttle is moved. In fact, in some cars the driver learns to use this facility by: •  Moving the throttle slowly when a down-change isn’t needed; •  Quickly moving the throttle a short distance when a one-gear down-change is wanted; •  Quickly moving the throttle a longer distance when two-gear down-changes are wanted. With the DTT able to control anything that can be electrically turned on and off, the driver will be able to activate (either consciously or unconsciously) a whole range of devices. output of the throttle position sensor and confirm that it varies over a 0-5V range when the throttle is moved. That done, install link LK1 in the “L/H” position so that the circuit triggers with increasing sensor voltage (ie, for quick throttle presses). You can now connect ignitionswitched +12V, earth and the throttle position signal to the DTT. Note that to get the throttle signal, you simply tap into the throttle position output wire – you don’t need to cut it. This latter connection can be made either at the ECU or at the throttle body itself. Next, adjust the lefthand pot (sen- sitivity) fully anti-clockwise and the righthand pot (timer delay period) fully clockwise – this increases the sensitivity of the DTT to throttle changes and reduces the timer’s “on” time to a minimum. (Note that both these pots are multi-turn so they don’t have a distinct end “stop”.) Now turn the ignition on but don’t start the car. Wait five seconds (the DTT has an ignition-on reset pause), then quickly push down on the throttle and check that the relay pulls in and that the LED lights. The relay should then click out (and the LED go off) fairly quickly, so adjust the righthand siliconchip.com.au One very effective use for the Delta Throttle Timer is to operate an auto trans power/economy button. When the driver uses quick foot movements, the transmission automatically selects power mode, while slow accelerator movements keep the transmission in economy mode. On the road, it works brilliantly! pot anticlockwise and again push down quickly on the throttle. This time, the “on” time should be longer. The next step is to adjust the lefthand pot clockwise until the DTT responds only when the throttle is being pushed down with “real life” quick movements. That done, move LK1 to the H/L position and confirm that the DTT now responds only to quick throttle lifts. Finally, move LK1 back to the L/H position if you want the circuit to trigger on a rising sensor voltage. Setting Up Setting up the DTT is also easy. Normally, you’ll find that driving on the road actually involves different speeds of throttle movement than used during the static set-up, so the sensitivity control will need to be ad- Fig.3: here is a typical connection set-up. The Delta Throttle Timer is fed ignitionswitched power and earth (chassis) connections. The signal input is wired to the throttle position signal. One of the relay’s Normally Open connections is also made to ignition-switched 12V while the adjacent Common is connected to a turbo boost control bleed solenoid. The other side of the solenoid is earthed. When the car is being driven with quick throttle movements, the solenoid will open, bleeding more pressure from the wastegate line and so increasing turbo boost. The solenoid in this example could be replaced with an intercooler water pump or fan, or – in a track car – even a brake cooling water spray. justed accordingly. The length of time that you set the timer to operate for will depend very much on what you are controlling. The prototype was used to automatically activate the Power mode in an auto transmission, an easy task to accomplish. All you have to do is wire the Normally Open (NO) and Common (C) terminals of the relay in parallel with the Power/Economy switch (this still allows the switch to be manually used as an over-ride). In this application, a DTT timer “on” period of about 7.5 seconds was ideal – any longer and sometimes the car would hang on too long in third gear before finally changing up to fourth, while lesser time periods meant that sometimes the DTT would click out of Power mode while the driver was still pushing hard. Incidentally, the driveability of the car was transformed by the use of the DTT in this way – after all, it’s a bit like having a little man sitting on the centre console, ready to push in the Power/Economy button every time you slam the throttle down fast! The PC board fits straight into a 130 x 68 x 42mm jiffy box, so when the system is working correctly, the board can be inserted into the box and  tucked out of sight. Uhh Ohhh – It Won’t Suit All Cars As constructed, the DTT will work with a throttle-position sensor that has an output that varies within the 0-5V range. Just about all cars use sensors that increase in voltage with throttle opening. However, the DTT can also be used in cars where the sensor voltage decreases with an increasing throttle opening (just move link LK1 to the H/L position to trigger with decreasing sensor voltage). What if you want to use an input signal that rises as high as 12V? In this case, zener diode ZD2 can be replaced siliconchip.com.au with a 470kΩ resistor. This may reduce sensitivity to changes but it should be compensated for by the larger input voltage and can also be adjusted with VR1. A larger capacitor at pin 1 of IC1a will also help solve this. However, some older cars use a throttle position switch, rather than a variable sensor. The DTT cannot be used with throttle position switches, so before buying the kit, the first step is to measure the output of the throttle position sensor. This can be done with the engine off (but the ignition on) by back-probing the throttle position sensor signal. With one multimeter probe earthed, you should be able to find a wire coming from the connector that has a voltage signal on it that varies somewhere within the 0-5V range as you manually twiddle the throttle. Cars with electronic throttles still normally have a throttle position sensor whose output can be used in the same way, although when back-probing to find the right wire, the throttle should be moved by use of the accelerator pedal, rather than by hand. PERFORMANCE ELECTRONICS FOR CARS 91