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Programmable Electronic Ignition System For Cars From time to time, many enthusiasts wish that they could vary the ignition advance curve or alter the dwell angle on the distributor of an old car or motorbike. This simple but sophisti­cated system will readily meet those needs. By ANTHONY NIXON This user programmable ignition system can be easily in­tegrated with the SILICON CHIP High Energy Ignition System (see May 1988), or readily adapted to suit other systems. Its main features are listed in Table 1. As shown in the photographs, the Ignition Programmer is built on a small PC board which carries a keypad. All data is entered via this keypad, so that 22  Silicon Chip new advance curves and dwell angles can be quickly programmed. To simplify the circuit and make construction easy, the unit is based on the versatile PIC16C84 microprocessor. The following parameters can be programmed into the system: • The revs (RPM) at which ignition advance begins; • The revs (RPM) for full advance; • • • • • • Maximum advance angle; Rev limit; Dwell angle; Vacuum advance; Number of cylinders; and A 2-digit security code. A useful feature of the system is that it allows two sets of data to be entered, either of which can be selected when the ignition is turned on. For example, the module can accommodate an engine which runs on both petrol and gas, as it allows the timing to be quickly changed for these different fuels to get the best performance. How it works The circuit (see Fig.1) is fairly simple, thanks to the PIC microprocessor (IC1). In operation, ignition timing information from the points Fig.1: the circuit is based on a PIC16C84 programmed microprocessor (IC1). This processes timing information from the points (or some other pick-up) and drives the High Energy Ignition System to switch the coil. Table 1: Main Feat ures • User programmable • Keypad data entry • Security coded (2 di gits) • Can store two sets of data • Tachometer drive ou tput • Points or other sens or input • Automatic coil curre • • nt switch nning off if motor not ru 7-segment LED di splay LED indicator for initial timing setup conditioning circuitry on the High Energy Igni­ tion module is fed into pin 1 (RA2) of IC1, while the ignition coil is controlled from pin 2 (RA3). This pin 2 output drives the coil via the “business-end” of the High-Energy Ignition System. The keypad used is a standard 12key unit with * and # symbols. Its rows connect to the RB3-RB6 outputs of the microprocessor, while its columns go to RB0-RB2. As it operates, the microprocessor alternately takes its RB3-RB6 outputs high and low. Thus, when a key is pressed, the logic level is sensed by one of the inputs RB0RB2 and the microprocessor takes the appro­priate action. For example, if key “3” is pressed, then RB3 of IC1 (pin 9) will be connected to RB2 (pin 8). Resistors R5-R7 (10kΩ) normally pull RB0-RB2 low. RA4 (pin 3) of IC1 is the vacuum advance input, while S1 is a micro­switch which is actuated by the vac­ uum advance motor (see photo). When the manifold vacuum is high, S1 is held open and RA4 is pulled high via R8 (10kΩ). Conversely, when the vacuum is low, S1 is closed and RA4 is pulled low so that the microproces­sor retards the timing. The 7-segment display is driven from IC2, a 74HC164 serial-to-parallel shift register. This receives serial information from pin 17 (RA0) of IC1 and is clocked from pin 18 (RA1). It displays such things as errors, programmable system variables and which set of data will be used. IC3, an MC34064 undervoltage sensing circuit, is used to ensure that the microprocessor resets reliably when the ignition is turned on. An 8MHz crystal, in conjunction with C6, C7 & R4, sets the microprocessor clock, while LED1 is driven from pin 13 (RB7) to provide points status indication (ie, it indicates whether the points are open or closed). The power supply uses a series diode (D1) for reverse polarity protection, a zener diode (ZD1) to clip any large spikes, and a 5V 3-terminal regulator (REG1). The latter provides a +5V supply rail for the ICs. Fig.2 shows how the Programmer Module interfaces with the SILICON CHIP High Energy Ignition System. As shown, the voltage across the points is filtered and fed to Q2’s base via D5 and a 10kΩ resistor. The signal at the collector has a 5V logic level and this is the “POINTS” input signal to the microprocessor on the programmer module. The “COIL” output from the programmer module is used to trigger IC1, the MC3334 ignition chip. IC1 in turn drives Q1 which is the coil switching transis­tor. Zener diodes D1-D4 protect Q1 from the high voltage spikes generated by the back EMF of the coil. Ignition timing In older engines, the centrifugal force generated by weights spinning in the distributor causes the engine March 1996  23 Fig.2: here’s how the Ignition Programmer module interfaces with the High Energy Ignition System. The coil output triggers the MC3334 ignition chip (IC1) and this in turn drives the coil switching transis­tor (Q1). timing to advance with increasing revs. Additionally, a vacuum advance mechanism increases the advance as the manifold vacuum rises. This either adds to or subtracts from the centrifugal advance, so that varying degrees of advance are obtained for different engine speeds and loads. Electronic advance In this system, the centrifugal advance is calculated according to engine RPM, while the vacuum advance is either on or off, as determined by the logic level on the vacuum advance input (RA4, pin 3) of the microprocessor. Because the advance is now determined electronically, the mechanical centrifugal advance mechanism in the distributor is clamped in the fully advanced position. To do this, the advance weight return springs are removed and the weights themselves are wired so they are held in the fully out position. In addition, the movable vacuum advance plate must be clamp­ ed so that it can’t move when the vacuum actuator is removed. In operation, the Ignition Programmer retards the ignition timing from its preset maximum value, to give the correct amount of advance to suit the operating conditions. As already mentioned, microswitch S1 is operated by the vacuum advance motor. It operates when the required vacuum is reached in the intake manifold (note: this system is also used on some production engines). 24  Silicon Chip Rev limiting is achieved by excessively retarding the igni­tion when the preset value is reached. All other variables are then ignored until the engine revolutions fall below this value. Microprocessor functions Instead of generating look-up tables for engine data, the program calculates a set of variables based on the data entered by the user and stores these in the PIC’s internal EEPROM. When the motor is sensed to be running, the microprocessor uses these variables to generate the timing of the output waveform. Some of the microprocessor’s ignition functions include monitoring the engine RPM, advance timing, dwell pulse width, maximum RPM, vacuum advance pulse width and number of cylinders. As all but the last of these are dynamic and constantly changing, the processor has to continuously recalculate new data. It is interesting to note that to create the various pulse widths and functions while the engine is running, the micropro­cessor only executes about 50 bytes of code and takes about 30µs to do it. Most of the program memory is taken up by the user interface, while the rest is used for data generation, the serial display and setup. When the ignition routine is first activated, the coil is turned on. If the motor is not started within 10 seconds, the coil will switch off and the system will enter MENU mode. This eliminates the possibility of any damage to the coil caused by leaving the ignition on, without the motor running. The coil will also be switched off if the motor stalls. In this case, the system will stay in the ignition routine and wait for the engine to be restarted or the power to be switched off. Construction The Ignition Programmer is easy to build, since all the parts except for microswitch S1 are installed on a PC board coded 05103961. Fig.3(a) shows the parts layout on the PC board. As always, check the PC board for open circuit or bridged tracks before you begin assembly. This done, fit the resistors, diodes and sockets for IC1 and IC2, then install the capacitors and other components. The LED display plugs into a wire-wrap socket (install this at full lead length), while the keypad plugs into an 8-pin header socket. Make sure that the LED display is correctly oriented when plugging it into its socket – it must be mounted with the decimal point(s) towards the bottom of the board. The 8MHz crystal can be mounted either way around but take care with the polarity of the ICs and LED1 – the anode lead of LED1 will be the longer of the two. It will be necessary to solder a wire to the +5V stake which is adjacent to pin 18 of IC1 before you fit the keypad. The keypad on the prototype was secured using machine screws and nuts (use nylon washers on the track Fig.3(a): install the parts on the PC board as shown here and take care if using a different keypad to that shown – see text. side of the board, to prevent shorts). Adjust the assembly so that the keypad is parallel to the PC board when it is plugged into its pin header socket. There’s just one wrinkle here – many keypads have their connections at the bottom instead of at the top. If you have this type of keypad, then it’s simply a matter of running a length of 8-way ribbon cable between the key­pad and the PC board. Note, however, that the pin connections to the keypad matrix will differ from keypad to keypad. The numbers Fig.3(b): this is the full-size etching pattern for the PC board. Check the board carefully for defects before installing any of the parts. in brackets on the circuit diagram (Fig.1) indicate the connections for a Jaycar keypad (Cat. SP-0770) – (ie, pin 2 of the keypad goes to pin 6 on the PC board, pin 7 goes to pin 8, etc). If you buy some other keypad (eg, the Altronics Cat. S-5381), then use the data supplied with the unit to determine the connections. Once the assembly is complete, check all your soldered joints carefully and check the polarity of D1. When you are satisfied that all is OK, connect 12V from a power supply or car battery to the terminals adjacent to the keyboard connector. Installation The exact installation will depend on your particular vehi­cle. If the unit is going in a car, the programmer could be mounted on the dashboard or centre console. Note that the microprocessor board should not be installed under the bonnet, as the components used are not rated for high temperatures. For a motorbike installation, the unit could be mount­ed in a weatherproof box on the handle­bars. Be sure to run all wiring in a professional manner, using proper automotive connectors to ensure reliability. Fig.4 shows how the unit is interfaced to the SILICON CHIP High Energy Ignition System. Note that it will be necessary Fig.4: this diagram shows how the Ignition Programmer is connected to the High Energy Ignition (HEI) module. Note that it is necessary to remove some parts from the HEI board if you are adapting an existing unit. March 1996  25 Make sure that all parts are correctly oriented when building the PC board and don’t forget the wire link next to crystal X1. to remove a number of parts from the centre of the board if you are adapting an existing ignition module. Fig.5 shows the mounting details for the microswitch S1. It is mounted on a rightangle bracket which is attached to the vacuum motor. The arm of the microswitch sits in a slot cut into the vacuum motor actuator and, in the absence of vacuum, is normally held Fig.5: the microswitch (S1) is mounted on the vacuum motor using a right-angle bracket. At low vacuum (ie, ignition off or at high engine loads), the microswitch arm is held down. Conversely, when the manifold vacuum is high (ie, at light engine loads), the microswitch arm is released. 26  Silicon Chip down. When vacuum is present, the actuator moves upwards and the microswitch arm releas­es. Be sure to connect the leads to the microswitch contacts exactly as shown (ie, the lead from pin 3 of the microprocessor goes to the contact marked “NO”). As mentioned previously, the advance plate in the distributor must be clamped at the maximum advance position (see photo). When the ignition is timed (using a timing light), the vacuum advance must be disabled. This is accomplished by removing and blocking the vacuum hose, so that it can have no effect on the vacuum switch. To time the ignition with the engine stopped, turn the crankshaft to the correct position, then rotate the distributor until the LED just turns on. This indicates that the points have just opened. The LED will be off when the microprocessor detects that the points are closed. Note that because the LED drive signal frequency is propor­tional to the engine RPM, this signal can be used to drive a suitable tachometer. Operation When the module is initially powered up, it will enter one of three states. These are as follows: (1). If there is no valid data in the EEPROM, the system will enter the MENU mode and the display will show “-”. This is what should be displayed at the initial power up. (2). If there is valid data but no security code has been pro­grammed, the system will begin its ignition routine and wait until the motor is started. The display will show the selected data channel. If the “9” key is pressed before the motor is started, the system will exit the ignition routine and enter the MENU mode to enable the user to make data changes. This option will not work after the motor has been started. (3). If there is valid data and a security code has been pro­grammed, the display will be blank and the system will not oper­ ate until the security code is entered. It will then show the selected data channel. If a mistake is made when entering the first digit, you can press the “#” key, then enter the digit again. This function does not work for the second digit, however. If it is entered incor­ rectly, the microprocessor shuts down until it is reset by turn­ing the power off and on again. MENU access using the “9” key is as detailed in (2) above. The keypad used in the prototype has its connecting pads at the top and plugs directly into the connector on the PC board. If you use a Jaycar or Altronics keypad with the pads at the bottom of the unit, the connections will have to be run using ribbon cable. Note, however, that the pin connections to the keypads will be different (see text). Keypad modes (1) Keypad Power-up Mode: if key 7 is pressed while powering up, the alternative channel is selected (other keys have no function). (2) Keypad Security Mode (after power is first applied and if data is valid): Key Function # Enter/exit code entry 0-9 Code entry (2 digits) * No function (3) Keypad Ignition Mode (ignition on, engine not running and data valid): Key Function 9 Enter menu mode Other No function When the system is initially turned on and no data has been entered into the internal EEPROM, the ignition won’t work. The system switches to MENU mode automatically and this is indicat­ed by the display coming on with only the centre segment lit. When in MENU mode, the keypad functions are as shown in the follow­ ing list: This close-up view shows how the microswitch arm is normally held down by the vacuum motor actuator. The common contact (COM) of the microswitch is connected to ground, while the NO contact goes to the PC board. March 1996  27 are shown. Data needs to be entered in the following manner, taking care to enter the digits properly and in the correct sequence: Variable Data Digits Allocated Start advance RPM 800 4 Finish advance RPM 2000 4 Advance angle 30° 2 Cylinders 2 2 Dwell angle 30° 2 Rev limit RPM 5000 2 Vacuum advance angle 10° 2 Security code 59 2 Because all timing in now controlled electronically, the advance plate inside the distributor must be securely clamped in the fully advanced position. In effect, the Ignition Programmer retards the timing from this preset maximum to give the correct value according to engine speed and load. Key 1 2 3 4 5 6 7 8 9 * 0 # Menu Mode Clear EEPROM Clear RAM data Read RAM data Write EEPROM data to RAM Enter new data to RAM Clear display No function Display data set selected at power-up (1 or 2) No function Create ignition data No function Exit to ignition A more detailed explanation of these various keypad functions is as fol­lows: • Key 1: Clears the user data stored in EEPROM. • Key 2: Clears the user data stored in RAM. • Key 3: Displays the data stored in RAM. Each data value entered has a letter assigned to it. A decimal point lights with the letters, to help differentiate between them and the numbers while they are being viewed. The data functions indicated by the let­ters are as follows: 28  Silicon Chip A. – RPM at start of advance b. – RPM at end of advance C. – Advance angle d. – Number of cylinders E. – Dwell angle F. – Rev limit G. – Vacuum advance angle H. – Security code To cycle through the data, press the “*” key. After the security code has been shown, the display wraps around to the RPM at start of advance again. To exit this display mode, press the “#” key. No other keys has any effect while reading data. A typical example display is as follows: A.0800, b.2000, C.30, d.02, E.30, F.50, G.10, H.59. Key Data Read 0-9 No function * Cycle to next data # Exit data read routine • Key 4: Gets the data from EEPROM and puts it into RAM. To view this data, press the “3” key and use the “*” key to cycle through the data, as explained above. Any data previously in RAM will be overwritten. • Key 5: Enters new data into RAM. Initially, an “A” will be dis­ played to indicate the first data entry. For simplicity, and as internal memory is limited, no further letter delimiters This data is entered exactly as follows: 0800 2000 30 02 30 50 10 59 There are a few things to note here: (1) No further letter delimiters after A are shown; (2) After entering the security code, “-” is displayed, indicat­ing the end of data entry; (3) There are leading zeros for the Start Advance RPM and for the Cylinder; (4) 50 is entered for the 5000 RPM limit; and (5) Make sure that you don’t forget the security code! If valid data is detected on power-up with a non-zero value in the security code, then this code must be entered when the system is to be used –eg, turn ignition on, press #, press 5, press 9 (code from data above). The ignition routine will now begin and the display will show the data set selected. If an incorrect code is entered, the ignition routine will not begin and no further response will be available from the keyboard. Turning the ignition off and then on again will allow the code to be re-entered. If you forget the code, the only way to gain access to the system is to start entering the 100 combinations one by one. Another example, this time with no security code, is shown below: Variable Data Digits Allocated Start advance RPM 650 4 Finish advance RPM 1500 4 Advance angle 12° 2 Cylinders 8 2 Dwell angle 0° 2 Rev limit RPM 4500 2 Vacuum advance angle 9° 2 Security code None 2 Example Programming Sequence A complete programming sequence (with no data entered) is as follows: Action Turn power on Press 5 Enter all data When finished Display A DATA - Reviewing Data Press 3 A ? DATA - Press * Press # Calculate & Store Data Press * if OK if error & delimiters finish reading display flashes ? if OK when finished if error ? A ? DATA - if OK if error if OK if error & delimiters finish reading Review EEPROM Press 4 Press 3 Press * Press # To program the second data set, first turn the power off and then turn it on again with key 7 pressed. The data is then programmed in and reviewed exactly as set out above. This data is entered exactly as follows: 0650 1500 12 08 00 45 09 00. As well as the previous items noted, if a zero dwell angle is entered, then a 1ms dwell angle will be set automatically. If any angle is calculated to be less than 1ms, then 1ms will be used. In addition, as the engine RPM increases, a point will be reached when the dwell width is theoretically less than 1ms. When the microprocessor detects this, it sets the minimum to 1ms. Important note: the dwell angle referred to above is the angle through which the points are open and not the angle through which they are closed, as is normally the case. The dwell angle from any input device has no effect on the system dwell setting. However, it is good practice to set the points normally, as speci­fied by the manufacturer. The microprocessor debounces the input, whether points or electronic sensors are used. • Key 6: Clears the display, so that it shows “-”. • Key 7: No function. • Key 8: Shows current data set selected (1 or 2). • Key 9: No function. • Key *: Calculates and stores, in EE­ PROM, new data that the system will use when the ignition routine is active. Valid data must have been enter­ed by the user. Care should be taken when choosing this data, as values which are too far away from standard may not work with the system. Memory constraints prohibit all but minor error checking of input data. If the number of cylinders is entered as zero then an error will occur in the calculations, as this will result in an inter­nal division by zero. Data entry can be aborted by pressing the “#” key. If this is done, no calculations can occur and there will be no data in RAM which can be read. Nor can it be stored in EEPROM. PARTS LIST 1 PC board, code 05103961, 76 x 70mm 1 12-key keypad (see text) 1 8MHz crystal (X1) 1 8-pin PC male connector (6mm pins) 1 8-pin PC female connector (6mm shroud) 1 14-pin wire wrap IC socket 1 18-pin IC socket (for IC1) 4 3mm x 20mm bolts 12 3mm hex nuts 4 3mm insulating washers 9 PC stakes Semiconductors 1 PIC16C84 programmed microprocessor (IC1) 1 74HC164 shift register (IC2) 1 MC34064 power-on reset (IC3) 1 78L05 regulator (REG1) 1 1N4002 diode (D1) 1 1N4745 16V 1W zener diode (ZD1) 1 LTS312 common anode 7-segment LED display (DS1) 1 red LED (LED1) Capacitors 1 100µF 25VW PC electrolytic 1 47µF 25VW PC electrolytic 3 0.1µF 100VW MKT polyester 2 18pF ceramic Resistors (0.25W, 1%) 6 10kΩ 9 1.5kΩ 1 2.2kΩ 1 22Ω Note: the programmed micro­ processor can be purchased for $27.00 including postage from Mr. A. Nixon, 20 Eramosa Road East, Somerville, Vic. 3912. Note that the display will flash while it is calculating the new variables, then turn off when finished. One major limitation of the system is that the total value of the advance, dwell and vacuum advance angles must not exceed the angle between cylinders. If this did happen, the microprocessor would still be in the middle of controlling the timing sequence from the previous trigger when the points opened again. This in turn would force new parameters to be calculated, which would over­write the old ones and cause erratic operation. In practice, this is not a problem March 1996  29 angle of 15°, the dwell angle results in a distributor angle of 30°, and the vacuum angle results in a distributor angle of 15°. This gives a total distributor angle of 60°, which is well over the 45° maximum. A more suitable set of parameters would be: Variable Start advance RPM Finish advance RPM Advance angle Cylinders Dwell angle Rev limit RPM Vacuum advance angle Security code The completed unit can be installed on the dashboard or centre console, or fitted into a weatherproof case and mounted on a motorbike. Do not mount the unit under the bonnet, as the parts are not rated for high temperatures. unless some “out of the ordinary” values are entered, especially for an 8-cylinder en­gine. The following example explains this more clearly: Variable Start advance RPM Finish advance RPM Advance angle Data 800 2000 30° Cylinders Dwell angle Rev limit RPM Vacuum advance angle Security code 8 30° 5000 30° 59 The cylinder angle for an 8-cylinder engine is 45°. From the above data, the advance angle results in a distributor Data 800 2000 12° 8 20° 5000 10° 59 The total distributor angle now becomes 31° and this repre­sents reasonable ignition timing for an 8-cylinder engine. • Key 0: No function. • Key #: This key terminates the data entry mode while entering data. Alternatively, it exits to the ignition routine if valid data is available while in MENU mode. If a keypress error occurs, then ? will be displayed. Key­press errors are: (1) Pressing key 3 with no RAM data; (2) Pressing key 4 with no EEPROM data; (3) Pressing key * with no data entered; (4) Pressing key # with no valid SC data. Fitting The Programmable Ignition System To A Motorbike I have tested this system on a 1948 Harley Davidson motor­cycle which originally only had a twist grip advance retard on the handle­bars.I also replaced the points with a Hall Effect transducer and thereafter had a fully programmable, maintenance-free ignition system. The major problem was how to run it off a 6V supply and this was overcome with a small switchmode supply. Another problem that I encountered was that the microprocessor behaved erratically while the engine was running. The solution involved removing the old copper-core plug leads and replacing them with suppressed ones. The program as it stands at the moment can only support distributors 30  Silicon Chip that have even spacing between cylinder angles – which covers most vehicles. However, engines that have irregular spacing (eg, Harley V Twins with two cylinders and a 45° angle) will fool the processor into retarding the timing for one of the cylinders. This is because the processor will calculate an ad­vance value for one cylinder but the calculated value for the other cylinder will be different because the two cylinders are not equally spaced at 180° around the crankshaft. In my case, a spe­ cial program was written to cater for this. If you want to eliminate the points, one option is to strip down the existing distributor and modify it for electronic operation. Alternatively, you can use a secondhand electronic unit from a wrecker if one is available. One advantage of keeping the points is that if the electronics decide to fail, the points can be connected directly to the coil and the ignition retarded (by rotating the distributor) to provide a limp-home mode. The next stage of development would be to eliminate the distributor completely and use the crank position as the timing reference. A crank sensor is certainly favourable when it comes to installing an electronic system but cost is another considera­tion – a “distributorless” ignition requires one dual output coil for every two cylinders and these would be fed by their own driver circuits, which in turn would be con­trolled by dedicated pins on the microprocessor.