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Chapter 23 Intelligent Turbo Timer This turbo timer sets the engine idle-down time to match how hard you have been driving! T he trouble with normal turbo timers is that they usually have a fixed idle-down time. It doesn’t matter if you have been driving like a maniac or just trundling around – either way, the engine will idle for a preset period (eg, two or three minutes) after you’ve come to a halt. However, since a turbo really only needs a cool-down period after it has been working hard, a fixed turbo idle-down period is often unnecessary. This Intelligent Turbo Timer doesn’t have that problem. Instead, it actually monitors how hard the car has been driven and then sets the idling time to match. Wiring is easy and the timer can be configured to suit your particular application. What It Does The Intelligent Turbo Timer uses a heavy-duty relay that has its con152 PERFORMANCE ELECTRONICS FOR CARS tacts wired in parallel with the ignition switch. If an idle-down time is required, this relay quickly closes when the ignition key is turned to the “off” position, maintaining power to the ignition circuit and so keeping the engine running. When the automatically selected idle-down period has elapsed, the relay opens, turning off the engine. LED1 is illuminated when the engine is running in its idle-down configuration. If desired, this LED can be mounted on the dash or it can be left out. A manual “reset” switch can be fitted which allows the engine idle-down period to be cancelled when it is pressed. This can also be mounted on the dash. The length of time that the engine idles after the ignition key has been turned off depends on two factors: (1) the maximum idle-down period that Main Features •  Idle period varies according to driver behaviour •  Adjustable maximum idle period •  Cancel (reset) switch •  LED timing indicator •  Engine load sensor input •  High input impedance for sensor load input •  Adjustable threshold voltage for load input signal •  Up or down “sense” selection for load input signal •  LED over-threshold indicator •  Diagnostic timer voltage output •  Optional second relay for bypassing alarms has been selected on a multi-position switch; and (2) the way that the car has been driven. siliconchip.com.au Fig.1: use this diagram and the photos of the completed project when assembling the PC board. Take particular care with the components that are polarised – these include the transistors, ICs, diodes, zener diodes, LEDs, electrolytic capacitors, REG1 and the BCD switch. This diagram also shows the external connections that can be made (see text for details). Note that link LK1 is not required in most applications. Switch S1 is used to select the maximum idle-down period, which can range from 15 seconds to 15 minutes, in 16 steps (0 to 9, A to F). For example, if you want the car to have an idle-down period that is never longer than five minutes, S1 would be set to position 9. If you want nine minutes, set the switch to position C. Table 1 shows the full range of settings. Load Sensor Input Just how hard the car is being driven is monitored by a load sensor input from the engine. Normally, this will be the air-flow meter output signal voltage but in cars with frequencyoutput air-flow meters, this signal can be taken from the oxygen sensor, MAP sensor or throttle position sensor. In fact, any voltage that varies with engine load within a 0-12V range can be used on this input. A multi-turn trimpot (VR1) is provided to adjust the sensitivity so that the Intelligent Turbo Timer can work with such a wide range of input load voltages. To set this sensitivity level, you need to watch LED2 while the car is being driven. VR1 is then adjusted so that LED2 lights only when the car is being driven hard. Normally, this point is set so that siliconchip.com.au Make sure that all polarised components are correctly orientated when assembling the PC board. All external wiring connections are made via screw terminal blocks. the LED lights only when the car is on boost (more on set-up below). The engine load at which this LED lights is called the “threshold”. The Intelligent Turbo Timer monitors how long the engine load exceeds this threshold over a 7-minute period. This information is constantly updated so that when the ignition is switched off, the Intelligent Turbo Timer has a PERFORMANCE ELECTRONICS FOR CARS 153 How It Works The basic component in the circuit is the microcontroller (IC1). This monitors the engine sensor signal via op amp IC2a and determines the timer period from this. IC1 also monitors the ignition voltage at its RA0 input and checks when the ignition is switched off. The idle-down time is set by switching on Relay1 to reconnect the ignition supply. A reset switch connected to the RB1 (pin 7) input can be used to cancel the idle-down period and switch off the engine. The ignition voltage is monitored via the normally-closed contacts (30 & 87a) which connect to the ignition circuit in the car. When the ignition is switched off, the voltage at the 87a contact is pulled low via a 1kΩ resistor. This voltage is detected at the RA0 input of IC1 (pin 17) and so IC1 switches on the relay which closes the normally-open contacts (30 & 87) and opens the 87a contact. This keeps the RA0 input low. By the way, these rather odd contact numbers are stamped into the standard automotive relay specified for this project. The voltage to the RA0 input is filtered using a 100kΩ resistor and 100nF capacitor, to prevent short voltage spikes from triggering IC1. The 39kΩ resistor to ground attenuates the voltage and is included so that the ignition voltage required to trigger the RA0 input is around 2V. If the resistor was not included, the ignition voltage would need to fall to below 0.6V before triggering IC1. The higher voltage ensures more reliable detection of the ignition switch off. IC1 is able to control the ignition by bringing its RA1 output high to switch on transistors Q1 and Q2. Transistor Q1 drives Relay1 which closes the above-mentioned normally-open contacts (terminals 30 and 87). After the timing period, the RA1 output goes low and switches off the relay. This opens the 87 contact on the relay and the engine switches off. The diode across the relay coil is there to quench the reverse voltage that occurs when the relay’s coil current is switched off. Transistor Q2 and Relay2 (if used) switches on and off at the same time as 154 PERFORMANCE ELECTRONICS FOR CARS Relay1. LED1 lights when this transistor is on, indicating that the Turbo Timer is extending the engine running time. LED1 goes off after the timing period. This extra relay can be connected if required, to bypass any ignition disabling circuitry that may be in place when the ignition key is removed. If an alarm is fitted, the ignition input can be taken from the 87a contact of Relay1. The maximum timing period is set using rotary switch S1. This has 16 positions labelled from 0 through to 9 then A, B, C, D, E & F. The selection on this switch is recorded by IC1 whenever power is applied. If you change the switch setting, the timing period will only change after power has been switched off and turned on again. As mentioned above, op amp IC2a monitors the engine sensor signal. It has a high input impedance, due to the 1MΩ series resistor and 2.2MΩ attenuator. This resistor divider attenuates the signal level to 0.69 of the applied input and will reduce a 12V signal to 8.28V. The 100nF capacitor filters the signal, preventing transient voltages being detected by IC2a which is connected as a comparator (ie, with no negative feedback). Trimpot VR1 has its wiper connected to pin 2 of IC2a. It is supplied with 10V due to zener diode ZD2, while the other side of the trimpot is connected to ground (0V). As a result, the wiper voltage can be adjusted between +10V and 0V. When the voltage at pin 3 of IC2a is above the threshold set by VR1, the output at pin 1 switches to +12V. This is monitored by IC1’s RA2 input via a 3.3kΩ limiting resistor. Internal clamping diodes at RA2 then limit the voltage on pin 1 of IC1 to +5.6V. Link LK1 at pin 6 of IC1 sets the comparator sense. It’s installed only if the engine sensor’s output voltage decreases with rising load. LED2 is the comparator indicator – it lights when the threshold has been reached and the idle-down period increases accordingly. Diagnostics A diagnostic output is available (from RA3) which indicates the relative idledown period that is current at the time. It provides a voltage ranging from 0V up to almost 5V. This voltage increases as the percentage of over-threshold increases over the 7-minute period. If there is an over-threshold for at least 25% of the seven minutes, the voltage will be almost 5V at the timing voltage output. This means that if the ignition were switched off at this time, the maximum idle time as set by S1 will occur. If the voltage is 2.5V, then the idle time will be half of the maximum time set by S1. And if the voltage is 0V, then there will be no idle time. The diagnostic output voltage is produced using a pulse width modulated (PWM) signal from the RA3 output of IC1. If RA3 is set at 0V all the time, then the voltage will be 0V. If RA3 is at 0V for some of the time and switches to 5V for the rest of the time, then the average voltage will depend on the ratio of how long RA3 is at 0V and how long it is at 5V. This voltage is filtered using a 22kΩ resistor and 100µF capacitor. Power for the circuit comes from the switched side of the ignition switch and is applied only when the ignition is on or while Relay1 is closed (ie, for the idle-down period). Diode D1 provides reverse polarity protection, while a 10Ω resistor and zener diode ZD1 are used to clamp transient voltages. The 470µF capacitor also filters the voltage. REG1 regulates the voltage down to 5V and the 10µF capacitor at REG1’s output decouples the supply. IC3 is a 5V supply supervisor which only switches high when the supply reaches 4.75V. This ensures that IC1 is reset correctly at power up. Finally, the circuit uses a 10MHz crystal to set the operating rate of IC1 and to provide a reference for the 7-minute timer and the idle-down period. Fig.2: the circuit diagram for the Intelligent Turbo Timer. Op amp IC2a monitors the engine sensor input signal and its output is fed to pin 1 (RA2) of microcontroller IC1. IC1 determines the cool-down period and controls the car’s ignition circuit via transistor Q1 and Relay1. Switch S1 sets the maximum cool-down period, while Relay 2 is used to bypass an engine immobiliser (if fitted) during the cool-down period. siliconchip.com.au siliconchip.com.au PERFORMANCE ELECTRONICS FOR CARS 155 RESISTOR COLOUR CODES Parts List 1 PC board coded 05car031, 123 x 60mm 1 SPDT 12V horn relay, Jaycar Cat. SY-4070 1 10MHz parallel resonant crystal (X1) 1 16-position BCD PC-mount rotary switch (S1) 1 momentary closed pushbutton switch (reset switch – S2) 5 2-way PC-mount screw terminals with 2.54mm pin spacing 1 18-pin DIP socket for IC1 1 1MΩ top-adjust multi-turn trimpot (VR1) 1 2-way pin header 1 jumper plug for 2-way header 2 6.3mm insulated female spade connectors 2 6.3mm male PC-mount spade connectors 1 50mm length of 0.7mm tinned copper wire 1 2m length red automotive wire 1 2m length yellow automotive wire 1 2m length black automotive wire Semiconductors 1 PIC16F84/20P microcontroller programmed with turbotmr.hex (IC1) 1 LM358 dual op amp (IC2) 1 MC34064 5V supervisor (IC3) 1 7805 5V 1A 3-terminal regulator (REG1) 2 BC337 NPN transistors (Q1,Q2) 2 3mm red LEDs (LED1,LED2) 1 16V 1W zener diode (ZD1) 1 10V 1W zener diode (ZD2) 3 1N4004 1A diodes (D1-D3) Capacitors 1 470µF 16V PC electrolytic 2 100µF16V PC electrolytic 2 10µF 16V PC electrolytic 4 100nF MKT polyester (code 104 or 100n) 2 22pF ceramic (code 22 or 22p) Resistors (0.25W 1%) 1 2.2MΩ 1 1MΩ 1 100kΩ 1 39kΩ 1 22kΩ 1 10kΩ 1 3.3kΩ 156 1 1.8kΩ 2 1kΩ 1 1kΩ 0.5W 1 680Ω 1 150Ω 1 10Ω PERFORMANCE ELECTRONICS FOR CARS Value 4-Band Code (1%) 5-Band Code (1%) 2.2MΩ 1MΩ 100kΩ 39kΩ 22kΩ 10kΩ 3.3kΩ 1.8kΩ 1kΩ 680Ω 150Ω 10Ω red red green brown brown black green brown brown black yellow brown orange white orange brown red red orange brown brown black orange brown orange orange red brown brown grey red brown brown black red brown blue grey brown brown brown green brown brown brown black black brown red red black yellow brown brown black black yellow brown brown black black orange brown orange white black red brown red red black red brown brown black black red brown orange orange black brown brown brown grey black brown brown brown black black brown brown blue grey black black brown brown green black black brown brown black black gold brown record of how hard the car was being driven for the last seven minutes. The idle timing period will be at its maximum if the engine sensor voltage was over the threshold setting for at least 25% of the seven minutes. If the over-threshold period is less than 25% of the seven minutes, the idle period will be reduced accordingly. However, the Intelligent Turbo Timer is even trickier than this. The actual idle-down period reflects not only what proportion of time over the last seven minutes the threshold was exceeded but also when in that seven minutes the hard driving occurred. If the threshold was exceeded just before switch-off, the idle period will be longer than if the over-threshold occurred earlier; eg, five or six minutes before switch-off. Specifically, the bias is such that if an over-threshold occurs within the final 1.75-minutes of the 7-minute period, the effect on the idle-down time is double the effect of an overthreshold occurring before this – ie, during the first 5.25 minutes of the 7-minute period prior to the ignition being switched off. Pretty tricky, eh? But you don’t need to worry about that – rest assured that all of the time you’re driving, the “mind” of the Intelligent Turbo Timer is busy thinking and watching! Fitting Only four wiring connections are needed to get the Intelligent Turbo Timer up and running. These are chassis ground, engine load sensor input, battery side of the ignition switch and ignition side of the ignition switch. Fig.1 shows these and the other connections. The chassis ground is easy – just connect the chassis ground connection on the Intelligent Turbo Timer to a good earth point on the car’s chassis. The load sensor input of the Intelligent Turbo Timer connects to the air-flow meter signal output (or MAP sensor, oxygen sensor or throttle position sensor). This sensor output can be found by using a multimeter to back-probe the air-flow meter (or MAP sensor, etc) until a wire is found that has a voltage on it that rises with engine load. (See the “Falling Voltage with Increasing Load?” panel, if you want to use a sensor that works the other way around.) Normally, just blipping the throttle is sufficient to vary the engine load Specifications Maximum idle periods .............................15s, 30s, 1m, 1.5m, 2m, 2.5m, 3m, 3.5m, 4m, 5m, 6m, 7m, 9m, 11m, 13m, 15m Engine input signal range ............................................................. from 0-12V Threshold voltage .........................................................adjustable from 0-12V siliconchip.com.au The Intelligent Turbo Timer is easy to build and easy to wire into the car. On the right is the Reset pushbutton that can be used to stop the engine during its idle-down time. However, because the Intelligent Turbo Timer always sets the idle-down period to match how you’ve been driving, it’s something you’ll rarely need to touch. enough to make identifying this wire easy. The wire doesn’t need to be cut – the Intelligent Turbo Timer engine load sensor wire just “T’s” into it. This connection can be made either at the sensor or at the ECU. Note that the sensor and ECU are unaffected by this connection. The two other connections can be made next. These must be made with heavy-duty wire as they carry a substantial amount of current. It is easier to find the right wires if you can access the back of the ignition switch. Using the multimeter, locate a wire going to the ignition switch that always has battery voltage on it. Then turn the 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. siliconchip.com.au ignition key to the “ignition” position and find another wire that has battery voltage on it when the key is in this position but zero volts (0V) on it when the key is turned off. Both these wires are likely to be thick, making their identification easier. Using a heavy-duty soldering iron or high-current crimps, connect a heavyduty wire to each of these ignition switch wires and then insulate these connections. Remember that battery voltage is always present on one of these cables – you should disconnect the battery when doing this work (and the rest of the wiring) because if this wire touches chassis ground, you could blow a major fuse or fusible link. For the same reason, never operate the Intelligent Turbo Timer in “bare board” form as these connections could easily short out to a metal component in the cabin. Instead, always install it in its box, leaving the lid off when doing the set-up. When you have made the connections to either side of the ignition switch, you can check that you have got it right by connecting these wires together when the engine is running. Then, when you turn off the ignition switch, the engine should keep running and then stop when you disconnect the wires. The “Reset” pushbutton can be mounted where it can be conveniently reached. It is wired to the terminal strip, as shown in Fig.1. LED1 can also be mounted on the dash – it is lit when the car is in its idle-down period. Setting-Up Setting-up the Intelligent Turbo Timer is easy but you should probably leave the module accessible for a few days afterwards so that you can do some fine-tuning if necessary. The first step is to set switch S1 Falling Voltage With Increasing Load? In most applications, where increasing engine load is associated with an increasing sensor voltage, link LK1 is not installed on the PC board. However, link LK1 can be installed if the voltage sensing direction needs to be reversed. This may be the case if you are using an engine sensor that decreases in output voltage with rising load. Another use might be if you have an old car that does not have engine management. In this case, the input could be connected to the coolant temperature sender unit so that the Turbo Timer will only operate when the sender reaches a certain temperature. Generally, these senders produce an output voltage that decreases with rising temperature. PERFORMANCE ELECTRONICS FOR CARS 157 Working With A Burglar Alarm switch off the ignition. LED1 should light and the engine should keep running for a period before switching itself off. If the engine keeps running longer than you’d like, increase the threshold setting of the pot a little. If the idle-down period is too short, decrease the threshold setting. You can also alter the idle-down period by changing the setting of S1 but start off by adjusting the trimpot. Try driving the car hard and then more gently for the last few minutes before switch-off – the idle-down time should then be shorter. Driven gently, there should be no idle-down time at all. Conclusion What if you have an alarm fitted? This has been taken into account in the design of the Intelligent Turbo Timer. A second relay – Relay2 – can be used to bypass the alarm system’s engine immobiliser. This relay’s coil connects to the bottom two terminals on the PC board – see Fig.1. If the 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). Finally, if the alarm requires an ignition signal, use the “alarm ignition input” connection on the Turbo Timer. to the maximum idle-down time that you think will ever be needed. Table1 shows the relationship between switch position and the maximum timing. In normal road cars, this will usually be Table 1 158 S1 Setting Max. Idle Period 0 1 2 3 4 5 6 7 8 9 A B C D E F 15s 30s 1m 1.5m 2m 2.5m 3m 3.5m 4m 5m 6m 7m 9m 11m 13m 15m PERFORMANCE ELECTRONICS FOR CARS about 5-7 minutes but if you race your car on a track, up to 15 minutes may be required. LK1 The next step is to drive the car while an assistant monitors the status of LED2. Trimpot VR1 should be turned VR1 until the LED lights only when the car starts being driven hard. This could be as the car comes onto boost, or if monitoring the oxygen sensor output, when the engine management system goes out of closed loop (as indicated by a mixture meter, for example) At this stage, don’t spend too long setting this control – you may well want to change it if the idle-down times prove to be shorter or longer than you prefer. By the way, LED2 will not light until a few seconds after the ignition is switched on. Test driving is next – drive the car hard, stop and then immediately At a cost much lower than commercial turbo timers (let alone intelligent turbo timers!), this project allows you to protect your turbo without having to spend time waiting around while the car idles unnecessarily. It’s also ideal if your turbo car is driven by someone less mechanically sympathetic than you are – no longer will you need to go on and on about “turbo cool-down periods” to someone who couldn’t care  less about them! S1 LED2 LED1 This photo shows from bottom left then anticlockwise: trimpot VR1, which allows adjustment of the engine load at which the Turbo Timer thinks you’re driving hard; LED1, which lights when the turbo timer is in its idle-down period; LED2, which lights when the engine load threshold is exceeded; and multi-position switch S1, which sets the maximum idle-on time. Just below IC1 is link LK1 which sets whether the timer senses a high or low voltage on its input as a high engine load. siliconchip.com.au