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Adaptive Turbo Timer By JOHN CLARKE If your car’s turbocharger has just been running, it is vital to allow the engine to idle for a few minutes before switching off. This Adaptive Turbo Timer will do the job automatically. It only operates when necessary and sets the idle time according to how hard you’ve driving. F OR MOST DRIVERS of turbo cars, having to leave the engine idling for a short period before switching off is often not particularly practical. Alternatively, they may simply forget to do it. Another problem is that in many cases, it is not really necessary. Your trip may have been rather slow and the turbo did not run. Or with brisk driving, the turbo may have been running but not in the last few minutes. At other times though, when the turbo has just been in use, the engine should be idled to allow cool-down. Why do car manufacturers recom42  Silicon Chip mend this idle period? It is all to do with prolonging the life of the turbocharger and particularly, its bearings. Switching off the engine immediately after turbo operation means that the turbo will still be spinning, as it runs at very high speeds. This also means that the bearings will then run without any fresh circulating oil from the engine. Any residual bearing oil will overheat and burn or tarnish due to the very high turbo temperatures. If this happens repeatedly, the result will be premature bearing wear. By contrast, idling the engine for a while before switching off will maintain the lubrication until the turbo cools. Whether to idle or just stop the engine when you park is a decision you must make every time, unless you install a turbo timer. However, most turbo timers will always idle the engine before switching it off, regardless of whether this is required or not. This is the case with the Turbo Timer published in the November 1998 issue of SILICON CHIP. Our new Adaptive Turbo Timer is different as it makes the decision as to whether to provide the cool-down period and if so, for how long. Its decisions are based on the vehicle’s recent driving history. If the turbo has not been used for the last 15 minutes, for example, no cool-down period will be provided. On the other hand, if the turbo has been active in the last few minutes, the engine will be idled for proper turbo cool-down. How does it know? So how does the Adaptive Turbo Timer monitor recent driving history and alter the cool-down time accordsiliconchip.com.au Fig.1: the circuit is based on microcontroller IC1 which monitors the sensor signal at its AN2 input. IC1 determines the cool-down period and controls the car’s ignition circuit via transistor Q1 and relay RLY1. Relay RLY2 is used to bypass an engine immobiliser (if fitted) during the cool-down period. ingly? It does this by monitoring an engine sensor that is load dependent. Typically, this will be an airflow sensor, a Manifold Absolute Pressure (MAP) sensor, an oxygen sensor, a throttle position sensor or a temperature sensor. Only one sensor is needed to provide this engine information. In operation, the Adaptive Turbo Timer monitors the sensor’s signal over a period of time and tallies up the amount of time the signal is above and below a preset value. To do this it samples the sensor signal 256 times over this tally period. The tally period is a minimum of five minutes but can be up to 15 minutes, depending on the maximum cool-down timer setting. The sensor signal is sampled every 1.17 seconds for a tally period of five minutes and once every 3.52 seconds if the tally period is set to 15 minutes. Note that the sensor is continuously siliconchip.com.au monitored but only the data within the tally period is relevant and older data is continually discarded. A sensor LED indicates whenever the preset value has been exceeded. The maximum cool-down period can be set anywhere between 0-15 minutes. The amount of time the sensor signal is above the preset value compared to the time under the preset value can be represented as a percentage. It is this percentage which largely determines the cool-down period. The monitored signal is also weighted according to how recent the data is. This means that the most recent quarter of the tally period has a greater effect on the timer cool-down period than earlier quarters. The actual weighting is such that the most recent quarter has four times more effect than the first quarter. Similarly, the second most recent quarter Main Features • • • • • • • • Automatic operation Cool-down period adapts to the turbo boost usage Adjustable maximum cool-down period Reset switch LED indication of current cooldown timeout period LED indication during cool-down LED indication of sensor level Sensor inversion selection has three times more effect and the third most recent quarter has twice the effect of the first quarter. The resultant cool-down period is indicated by a LED that has a brightness level that varies according to the percentage of full timeout period. So if the timeout is 100% of the setting, then the LED will be fully glowing. August 2007  43 Fig.2: follow this diagram to assemble and install the Adaptive Turbo Timer. Check that all polarised parts are correctly oriented and be sure to use automotive cable for all external connections. Note that the A & B connections at left should be run using heavy-duty cable as they carry the ignition circuit current. sleeve of heatshrink tubing. You can either mount the indicator LEDs on the instrument panel or they can be simply mounted on the PC board for use when setting up the timer. Circuit details This is the completed unit, ready for installation. You can either mount the LEDs on the PC board and use them during the setting-up procedure or you can mount them on the dash and connect them via flying leads. Lower percentages will have the LED glow at a lower brightness. When driving, this LED will be seen to vary in brightness according to the amount of time the turbocharger has run. It gives a good indication of just how much time the cool-down period will be when the engine is switched off. An Idle LED also lights during the cool-down period. Using it The Adaptive Turbo Timer is easy to use. Just drive the car and when 44  Silicon Chip you switch off the ignition, the Adaptive Turbo Timer will either allow the engine to switch off or run it for a further short period, depending on the amount of recent turbo use. However, if you wish, you can override the cooldown period at any time and switch off the engine at any time by pressing a reset switch. As shown in the photos, a small PC board accommodates all the main parts for the Adaptive Turbo Timer. This board can be mounted inside a plastic box or it can be wrapped in a Fig.1 shows the full circuit details of the Adaptive Turbo Timer. It’s based on a PIC16F88-I/P microcontroller (IC1) and this monitors the engine sensor signal at its AN2 input (pin 1). IC1 also monitors the ignition voltage at its RA0 input (pin 17) and checks when the ignition is switched off. The cool-down period is enabled by relay RLY1 which is connected in parallel with the cars’s ignition switch. Pushbutton switch PB1 is connected to IC1’s RB1 (pin 7) input and can be used to cancel the cool-down period and switch off the engine. The car’s ignition switch is monitored by RA0 (pin 17) via the normally closed contacts of relay RLY1 (30 & 87a). The input voltage to pin 17 is fed via an RC filter (100kW resistor and 100nF capacitor) to prevent any false triggering by transient voltage spikes. The 39kW resistor to ground attenuates the input voltage and is included so that the ignition voltage required to trigger the RA0 input is around 2V. This ensures faster and more reliable detection of the ignition switch off. Normally, when the ignition is switched off, pin 17 is pulled low via a 1kW resistor. However, when the ignisiliconchip.com.au tion is switched off and the micro has calculated that a cool-down period is warranted, its RA1 output goes high and switches on NPN transistors Q1 & Q2. Q1 drives relay RLY1 and this closes the normally open contacts (30 & 87) to reconnect the ignition supply to the engine. This happens so quickly that there is no faltering in the engine. At the end of the cool-down period, the RA1 output goes low and switches off the relay (thus turning off the engine). Diode D2 is connected across the relay coil to quench the spike voltage that occurs when the relay’s coil current is switched off. Q2 and the optional relay RLY2 is provided to bypass any after-market engine immobiliser that may have been installed until after the cooldown period. Q2 also drives LED3 to indicate that the Turbo Timer is providing cool-down time. LED3 goes off after the cool-down period. Note that if an alarm is fitted, it must have its ignition input signal taken from the 87a contact of RLY1. If this is not done, the alarm is liable to sound during the cool-down period. Cool-down setting Trimpot VR2 sets the cool-down period. Its wiper is connected to the AN6 input of IC1 (pin 13). VR2 provides a voltage between 0-5V and this is converted to a digital value within IC1. The cool-down period is zero when VR2 is fully anticlockwise and 15 minutes when it is fully clockwise. Test point TP2 is a convenient point to measure the setting of trimpot VR2. Table 1 shows the timeout voltages for several settings of VR2. For example, a setting of 333mV will provide a 1-minute cool-down period, a 1V setting will provide three minutes and a 5V setting will provide 15 minutes. The cool-down setting value is checked by IC1 whenever power is applied. This means that if you change the setting of VR2, the timing period will only change after power has been switched off and on again. Warning! Be sure to use the Turbo Timer only when your car is parked in the open. The reason for this is fairly obvious – your car’s engine exhausts carbon monoxide (CO) fumes while it is running and carbon monoxide gas is colourless, odourless and extremely poisonous. Never allow the engine to run on if the car is parked in a confined space; eg, a garage. If you do need to allow the turbo to cool, park the car outside instead until the engine cuts out and park the car in the garage later on. Engine sensor As mentioned above, the AN2 input (pin 1) monitors the engine sensor signal. The sensor input has a relatively high input impedance, due to the 100kW series resistor and 1MW trimpot VR1. VR1 attenuates the input signal level, while the 100nF capacitor provides a degree of filtering. In operation, the AN2 input signal is converted to a digital value within IC1 and compared to a 1V level. LED2 lights when ever the signal at AN2 is above or below 1V, depending on the “voltage sense” setting provided by link LK1. Alternatively, the signal threshold can be set to 100mV when link LK2 is inserted. This lower threshold is more suitable for the signal from an oxygen sensor. With LK1 out of circuit, the RB0 input (pin 6) is held high via an internal pull-up resistor. When LK1 is installed, it pulls the input to ground. This link is only installed if the engine sensor’s output voltage decreases with engine load. As stated earlier, the brightness of LED1 gives an indication of the cool-down period. It is driven using a pulse-width modulated (PWM) signal from pin 9 via a 470W current-limiting resistor. When the cool-down percentage is 100%, pin 9 outputs a nominal 5V and gives maximum LED brightness. Lower cool-down settings result in a PWM signal with reduced duty cycle and therefore reduced brightness from LED1. Input RB1 (pin 7) is normally tied to +5V via an internal pull-up resistor. When reset switch PB1 is closed, pin 7 is pulled close to 0V and this is detected by IC1 as a switch closure. IC1 operates from an internal 8MHz oscillator. This sets the operating rate of the micro and the clocking for the timers that tally the sensor input signal and provide the cool-down period. Power for the circuit comes from the switched side of the ignition switch and so power is applied only when the ignition is on or while relay RLY1 is closed (ie, during the cool-down period). Diode D1 provides reverse polarity protection, while a 10W resistor and zener diode ZD1 are used to clamp Table 1: Resistor Colour Codes o o o o o o o o o o o o siliconchip.com.au No.   2   1   1   1   1   2   1   1   1   1   1 Value 100kW 39kW 10kW 2.2kW 1.8kW 1kW 1kW 680W 470W 100W 10W 4-Band Code (1%) brown black yellow brown orange white orange brown brown black orange brown red red red brown brown grey red brown brown black red brown brown black red brown blue grey brown brown yellow violet brown brown brown black brown brown brown black black brown 5-Band Code (1%) brown black black orange brown orange white black red brown brown black black red brown red red black brown brown brown grey black brown brown brown black black brown brown brown black black brown brown blue grey black black brown yellow violet black black brown brown black black black brown brown black black gold brown August 2007  45 Working With A Burglar Alarm If an alarm is fitted to your car, this has been taken into account in the design of the Adaptive Turbo Timer. A second relay – RLY2 – can be used to bypass the alarm system’s engine immobiliser. This relay is connected to the bottom two terminals on the PC board. Where your alarm system disables the ignition by shorting it out, connect the relay between the alarm immobiliser output and the ignition system using the 30 and 87a contacts as shown at (A). Alternatively, if the alarm system open circuits the ignition, use the 30 and 87 contacts to reconnect the ignition as shown at (B). In addition, if the alarm requires an ignition signal, use the “To Alarm Ignition Input” connection on the Turbo Timer. the anode (longer lead) as shown on Fig.2. LEDs 1 & 3 are red while LED2 is green. Trimpots VR1 & VR2 can now be installed, followed by the two 3-way link headers for LK1 and LK2. REG1 is mounted horizontally on the PC board with its leads bent over by 90° to insert into the allocated holes. The regulator’s tab is then secured to the PC board using an M3 screw and nut, after which the leads can be soldered. Don’t solder the regulator’s leads before bolting it down, as this may strain the soldered joints as the nut is tightened. Once these parts are in, install the two independent 2-way PC-mount screw terminals. The 8-way block at the righthand edge can then be installed. It’s made up using six of the 2-way screw terminals. They connect by sliding the dovetail joints together before installing the assembly on the PC board. Finally, install the relay and the two spade connector terminals which are soldered directly to the PC board. Note that the relay’s mounting tab will have to be cut off before it is installed. Testing voltage transients. A 470mF capacitor then filters the supply after which it is fed to regulator REG1. REG1 produces a +5V rail to power the microcontroller, while the relays are powered by the vehicle’s battery. The 100mF capacitor at REG1’s output provides extra decoupling. Construction The Adaptive Turbo Timer is built on a PC board coded 05108071 and measuring 107 x 61mm. If you don’t like the idea of fitting it with a heatshrink sleeve, it can be housed in a standard plastic case measuring 130 x 68 x 44mm – the board simple clips into the integral side slots. Most of the external connections to the vehicle are made via PC-mounted screw terminal blocks. The exceptions here are the two external connections to the relay, which are run via PCmount spade connectors (necessary for the heavier current). Begin construction by checking the PC board for any defects (eg, shorted or open circuit tracks) and for the correct hole sizes. The holes for the 46  Silicon Chip screw terminal blocks will need to be larger than the 0.9mm holes for the other components – ie, about 1.2mm. Relay RLY1 requires slotted holes to accept its spade terminals. Fig.2 shows the parts layout on the board. Start the assembly by installing the resistors first, taking care to place each in its correct place. Table 1 shows the colour codes but you should also use a digital multimeter to check each resistor before inserting into the PC board. The diodes and the IC socket can go in next, taking care to orientate each with the correct polarity. The capacitors can then go in but note that the electrolytic types must be oriented as shown on Fig.2. Next on the list are the two transistors which can now be soldered into place. LEDs 1-3 can either be mounted on the PC board or mounted externally (eg, on the dash). Note that the LED mounting pads are also brought out to the screw terminal blocks, to make external mounting easy. If you are mounting the LEDs on the PC board, take care to orient them with Now for the smoke test. Initially, leave IC1 out of its socket and connect a wire so that you can open and close the circuit between spade terminals A and B. This simulates the car’s ignition switch. Next, apply +12V to the A terminal and 0V to the ground or chassis screw terminal. That done, use a multimeter to check the voltage between pins 14 & 5 of IC1’s socket – you should get a reading of 5V (anywhere between 4.85V and 5.15V is OK). If this checks out OK, switch off and install IC1 in its socket. Be sure to orient the IC correctly – the notched end goes to the left. Adjustments Initially, set VR2 to its mid position. This will provide a nominal 2.5V at TP2 for a 7.5-minute timeout. Jumper pins LK1 and LK2 should be fitted to their OUT positions. Apply power (+12V) again to the A terminal and close the connection between the A and B terminals (ie, connect A & B together). That done, you need to simulate a sensor signal by connecting a wire between the sensor input terminal and the A input. siliconchip.com.au Specifications Cool-down idle period: up to 15 minutes Recent driving history monitoring: 5 minutes or equal to cool-down setting. Recent driving history weighting: fourth ¼-period weighted by a factor of 4; third ¼-period weighted by 3; second ¼-period weighted by 2; first ¼-period weighted by 1. Sensor input adjustment range: 1.1-15V or 0.11-1.5V, selected with LK2 Sensor input threshold: 1V or 0.1V, selected with LK2 Sensor input sense: positive or negative, selected with LK1 Sensor input impedance: 1.1MW Next, adjust VR1 so that the voltage at TP1 is just over 1V and check that LED2 (the sensor LED) lights. If you now disconnect the sensor input from the A terminal, the sensor light will go out after a maximum of 1.8 seconds. Reconnecting the sensor input to the A terminal again should then turn the LED on again after a maximum of 1.8 seconds. You should now see LED1 (the “percentage timeout” LED) begin to glow and increase in brightness during the period that LED2 is lit. It will stop increasing in brightness when the sensor input is disconnected from the A terminal and LED2 goes out. (Note: the percentage timeout LED shows the current percentage of the cool-down timeout set by VR2). If you now disconnect the link between the A and B terminals, relay RLY1 should close (indicated by a click as the contacts close) and LED3 should light. The cool-down period will be up to 7.5 minutes but less if LED1 is not glowing at full brightness. LED1 will now begin to decrease in brightness until it extinguishes. At the end of the cool-down period, the relay will then switch off and LED3 will also extinguish. Installation When installing the Adaptive Turbo Timer in your car you will need to select a suitable sensor that changes its output with engine load. There are several sensors that can be used and these are listed below, in order of preference: (1) Airflow Meter: this type of sensor provides a good indication of engine load. High airflow means that the engine is being driven hard and the turbocharger would be expected to be siliconchip.com.au applying boost. Airflow sensors generally have a rising voltage with airflow that ranges from about 0.5V at idle through to about 4.5V at high engine loads. Note that some airflow sensors do not change in voltage but provide a change in frequency instead. A frequency output signal is unsuitable for use with this circuit. You can monitor the airflow signal by connecting a digital multimeter to its output and then driving the car. The voltage should change with engine load. If it doesn’t, you may be measuring the wrong wire or the output may be a varying frequency. (2) MAP (Manifold Absolute Pressure) sensor: this measures the air pressure at the manifold or at the air intake, the output voltage increasing with rising pressure – ie, with increasing engine load. MAP sensors generally cover the range of 0.5-4.5V. With turbo boost, the MAP sensor should provide higher output voltages than those derived without boost. (3) Oxygen Sensor oxygen sensors measure the air/fuel mixture by detecting the amount of oxygen present in the burnt fuel. Generally they produce a signal range of 0-1V, with the higher voltage meaning a rich mixture. For many cars, the engine runs rich when accelerating and so the signal could be used to indicate when the engine is being driven hard. However, some cars do not run rich under acceleration and remain running with stoichiometric mixture instead. In this case, the sensor would be unsuitable because its output essentially does not change. You can check the oxygen sensor output during driving by connecting a digital multimeter to it. Parts List 1 PC board, code 05108071, 107 x 61mm 1 UB3 plastic case, 130 x 68 x 44mm (optional – see text) 1 SPDT 12V horn relay (RLY1), Jaycar Cat. SY-4070 1 SPDT 12V horn relay (RLY2), Jaycar Cat. SY-4070 (optional) 1 momentary closed pushbutton switch (PB1) 6 2-way PC-mount screw terminals with 5.08mm pin spacing 1 18-pin DIP socket for IC1 2 3-way pin headers 2 jumper plugs 2 6.3mm insulated female spade connectors 2 6.3mm male PC-mount spade connectors 1 M3 x 10mm screw 1 M3 nut 2 PC stakes 1 2m length red automotive wire 1 2m length yellow automotive wire 1 2m length black automotive wire Trimpots 1 1MΩ top adjust multi-turn trimpot (VR1) 1 10kΩ horizontal mount trimpot (code 103) (VR2)) Semiconductors 1 PIC16F88-I/P microcontroller programmed with Adaptive Turbo Timer.hex (IC1) 2 BC337 NPN transistors (Q1, Q2) 1 7805 5V 1A 3-terminal regulator (REG1) 1 16V 1W zener diode (ZD1) 3 1N4004 1A diodes (D1-D3) 2 3mm red LEDs (LED1, LED3) 1 3mm green LED (LED2) Capacitors 1 470mF 16V PC electrolytic 2 100mF 16V PC electrolytic 4 100nF MKT metallised polyester (code 104 or 100n) Resistors (0.25W 1%) 2 100kΩ 1 1kΩ 0.5W 1 39kΩ 1 680Ω 1 10kΩ 1 470Ω 1 2.2kΩ 1 100Ω 1 1.8kΩ 1 10Ω 2 1kΩ August 2007  47 Table 2 The PC board can either be covered with heatshrink tubing (if you can find some large enough) or mounted in a standard plastic case as shown here. (4) Throttle position sensor: although not ideal, the throttle position sensor could also be used as it changes its output voltage when the throttle is pressed. (5) Temperature Sensor: older cars may not have any of the abovementioned sensors and so you could connect to the coolant temperature sensor instead. This will generally produce a high voltage when cold and reach a low voltage when the coolant is hot. Making the connection When making a connection to these sensors it is not necessary to cut the wire – just tap into it instead. The connection can be made at the ECU (Engine Control Unit) or at the sensor itself. The Adaptive Turbo Timer’s sensor input has a high impedance so it will not affect the operation of sensor it is connected to or cause problems with driveability. Once you have found a suitable engine sensor, the remaining connections to the Adaptive Turbo Timer can be made. The A and B connections need to be made using heavy-duty wire as they carry the ignition circuit current. It helps here if you can access the back of the ignition switch. Using a multi­meter, locate a wire going to the ignition switch that always has battery voltage on it. That done, turn the ignition key to the ON position and find the wire that now has battery voltage on it but reverts to 0V when 48  Silicon Chip the key is turned off. Note that when making connections, you should disconnect the car’s battery. This will mean that you will lose the settings in your car’s radio so be sure you have the security password to enable you to reset it when the battery is reconnected. The Reset pushbutton should be mounted in a convenient position (ie, within reach) on the dashboard. As mentioned, the indicator LEDs can also be dashboard mounted, so that the cool-down period and the time remaining can be readily monitored. Setting up You need to have access to the PC board in order to carry out the settingup procedure. That’s because you have to adjust the trimpots and be able monitor the LEDs (if they are on the PC board). Initially, you can set VR2 to the maximum cool-down period that you will need. Some guidance for this should be in your car’s user manual. It’s generally in the region of 4-7 minutes but some high-performance cars may need longer. The next step requires adjustments to be made while the car is driven and so a second person is required to assist with this. Get someone to drive the car while you monitor the sensor LED (LED2). Adjust VR1 so that the LED lights when the car accelerates quickly and the turbo boost comes on. Cool-Down Period VR2 Setting (Voltage At TP2) 15 minutes 5V 14 minutes 4.67V 13 minutes 4.33V 12 minutes 4V 11 minutes 3.57V 10 minutes 3.33V 9 minutes 3V 8 minutes 2.67V 7 minutes 2.33V 6 minutes 2V 5 minutes 1.67V 4 minutes 1.33V 3.5 minutes 1.17V 3 minutes 1V 2.5 minutes 0.83V 2 minutes 0.67V 1.5 minutes 0.5V 1 minutes 0.33V 30 seconds 0.17V 15 seconds 0.08V If you have connected the unit to the oxygen sensor, then LK2 may need to be placed in the “in” position so that the threshold voltage for sensing is 100mV (0.1V) instead of 1V. Also, for some sensors, the sense may be incorrect and the LED may light for light engine loads and turn off at high engine loads. In that case, place LK1 in the “IN” position to reverse the sensor sense. You will find that the percentage LED is invaluable for showing the amount of time the Adaptive Turbo Timer is expected to run. You can adjust the maximum cool-down period with VR2 to get the correct cool-down period with various driving styles. Note that any change with VR2 will not come into effect until the Turbo Timer is switched off and on again. When the unit is correctly adjusted, there should be no cool-down period if the turbocharger has not been used (ie, with normal driving). Cool-down should also not occur if several minutes have elapsed since the turbocharger was last used. Conversely, the cool-down timer should operate after SC hard driving. siliconchip.com.au