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This Programmable Ignition Timing Module is intended to be used in conjunction with our High Energy Ignition System as described in the June 1998 issue. It allows you to program the ignition timing of engines with points, Hall effect or reluctor distributors. By ANTHONY NIXON T his project was first introduced in the March 1996 issue of SILICON CHIP and it has proven to be very popular: there are now thousands of units in use. This article updates the project and clarifies the installation. Since its introduction, the design and software of the Programmable Ignition Timing module have gone through a number of changes to improve performance and the High Energy Ignition system was also updated in the June 1998 issue. These revisions have led to some confusion as to how the system should be connected and operated and this is why we have decided to 56  Silicon Chip update the project and completely re-present it. The Programmable Ignition Timing module is a small PC board comprising just two ICs, a handful of other components, a keypad and a small display. The simplicity and ease of construction of the circuit is made possible by using a PIC 16F84 microcontroller. Programming is simply a matter of entering data with the keypad while monitoring it on the display. Nine parameters can be programmed into the module: • The RPM at which ignition advance begins • Mid stage RPM • • • • • • • Mid stage advance RPM limit Rev limit advance Dwell angle Vacuum advance Number of cylinders A 2-digit security code To make the module even more useful, the second stage advance can be either positive or negative and you can store two sets of data which can be alternated while the engine is running. The benefit of this is that you can accommodate an engine that runs on petrol or LPG and quickly change the timing for these two fuels to get the best possible performance. Main Features             User programmable Two stages of advance Second stage advance can be positive or negative Keypad data entry Security coded (2 digits) Can store two sets of data Tachometer drive output Points or other sensor input Automatic coil cutoff if motor not running 7-segment LED display LED indicator for initial timing setup Preset RPM limiting Reproduced from the June 1998 issue of SILICON CHIP, the High Energy Ignition system has proved to be a winner – very good performance and highly reliable. The programmable ignition timing module described here is designed to directly interface with this HEI, although it can be adapted to other ignition systems including the Multi-spark CDI described in September 1997. Please note that while this project has been very popular, it is not intended for high performance vehicles, particularly those which already have engine management systems. What it does Fig.1 shows how the Programmable Ignition Timing (PIT) module is connected to the High Energy Ignition (HEI) system. In essence, the signal from the car’s points, reluctor or Hall effect pickup in the distributor is conditioned by the input circuitry of the HEI system and we use the conditioned signal to trigger the PIT module. Depending on its programming, each time the PIT module receives a Fig.1: this diagram shows how the Programmable Ignition Timing module is connected to the High Energy Ignition system, described in the June 1998 issue of SILICON CHIP. JUNE 1999  57 trigger pulse from the HEI, it delivers a delayed pulse to the HEI system to fire the ignition coil. Why are the ignition pulses delayed? In cars without engine management, the ignition timing (ie, the ignition advance curve) is controlled by centrifugal weights in the distributor. These cause the ignition timing to advance as the engine RPM increases. In addition, a vacuum diaphragm actuator mechanically increases the advance as manifold vacuum rises. When the PIT and HEI systems are employed together, the car’s centrifugal advance mechanism 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 moveable vacuum advance plate must be clamped so that it can’t move when the vacuum actuator is removed. Since the distributor is locked in the fully advanced position, the PIT module must provide a variable time delay in order to allow the engine to start and run. In practice, it provides quite a lot of delay when the engine revs are low and less delay when the engine revs are high. It also modifies the delay depending on whether the vacuum switch is open or closed. How it works Fig.2: the circuit is based on the PIC16F84 microcontroller. This processes timing information from the car’s distributor (points, Hall effect, etc) and varies the ignition timing accordingly. 58  Silicon Chip Fig.2 shows the circuit of the PIT module. The heart of the circuit is the PIC 16F84 microcontroller. It calculates the delay period for each ignition pulse, according to stored data which has been previously entered via the numeric keypad. The keypad has four rows and three columns (for 12 keys) and these are connected to seven inputs on the PIC, RB0-RB6; the columns to RB0-RB2 and the rows to RB3-RB6. When operating, the PIC alternately takes its RB3-RB6 outputs high and low. When any key is pressed, this low is then sensed by one of the RB0- RB2 inputs and the PIC takes the appropriate action. For example, if key “0” is pressed, then when RB6 is pulled high, it is connected through the key to RB2, which is normally held low by resistor R5. RA4 (pin 3) is the vacuum advance input and S1 is a microswitch that is Fig.3: this flow chart diagram shows the PIT module functions. activated by the vacuum actuator; ie, the standard diaphragm unit fitted to older distributors. When the manifold vacuum is high, S1 is held open and RA4 is pulled high via resistor R8. Conversely, when the manifold vacuum is low, as when the accelerator is wide open, S1 is closed and RA4 is pulled low and this causes the PIC to retard the ignition timing. The 7-segment LED display is driven from IC2, a 74HC164 serial to parallel shift register. This receives serial data from pin 17 (RA0) of the PIC and it is clocked from pin 18 (RA1). It’s parallel data output drives the 7-segment display to indicate such things as errors, programmable system variables and which set of data will be used. IC3 is an MC34064 undervoltage sensing circuit and it is used to ensure that the PIC resets reliably each time the ignition is turned on. An 8MHz crystal, in conjunction with C6, C7 and R4, sets the clock speed for the PIC, while LED1 is driven from pin 13 (RB7) to provide trigger pulse status. This LED will be on when RA2 (pin 1) is low and off when RA2 is high. The power supply uses a series diode (D1) for reverse polarity protection, a zener diode (ZD1) to clip any large voltage spikes and a 5V 3-terminal regulator (REG1). The latter supplies the 5V rail for the ICs and to the MC3334P on the HEI PC board. There can be quite a lot of interference coming from the engine bay via the wires connecting to the input and output pins on the PIC. Diodes D2-D7 together with resistors R17 to R19 and capacitors C8-C10 help shunt this interference back to the power supply. The IN5819 diodes specified are Schottky types and have a lower JUNE 1999  59 Parts List 1 PC board, code 05406991, 74 x 70mm 1 12-key keypad 1 8MHz crystal 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 10mm plastic spacers 4 3mm x 20mm screws 4 3mm hex nuts 6 PC stakes Semiconductors 1 PIC16F84 programmed microcontroller (IC1) 1 74HC164 shift register (IC2) 1 MC34064 power-on reset (IC3) 1 78L05 3-terminal regulator (REG1) 1 1N4004 diode (D1) 6 1N5819 Schottky diodes (D2-D7) 1 1N4745 16V 1W zener diode (ZD1) 1 LTS312 common anode 7-segment LED display DISP1) 1 red LED (LED1) Capacitors 1 100µF 25VW PC electrolytic 1 47µF 16VW PC electrolytic 3 0.1µF MKT polyester or monolithic 3 .01µF MKT polyester or monolithic 2 18pF ceramic Resistors (0.25W, 1%) 6 10kΩ 1 2.2kΩ 8 1.5kΩ 4 330Ω 3 100Ω 1 22Ω Note: the programmed 16F84 microcontroller can be purchased for $27, including postage, from Mr A. Nixon, 8 Westminster Court, Somerville, VIC 3912. Fig.4: two possible 2-stage advance characteristics which could be programmed into the module. These could enable a car to run on petrol or LPG, for example. turn-on voltage and faster turn-on times compared to normal diodes. In operation, the PIT module retards the advance by 45 crank degrees until the engine RPM matches the minimum RPM value set by the user. Then as the RPM rises above this point, the programmed amount of advance will be given. The timing is calculated this way so that one data set can have more or less advance than the other. Microswitch S1, if used, is operated by the vacuum actuator. It operates when the required vacuum is reached in the intake manifold. RPM limiting is achieved by missing every second spark when the maximum RPM value is reached. All other variables are ignored until the engine revolutions fall below this value. HEI system change As already noted, the PIT module is teamed up with the HEI system featured in the June 1998 issue of SILICON CHIP. When using the HEI with the PIT module, the connection shown in Fig.1 means that the collector of Q2 on the HEI PC board connects to pin 1 (RA2, trigger input) on the PIT board and provides the PIC with timing information. The PIT output, pin 2 (RA3), is connected to pin 5 of IC1 on the HEI board. In this configuration, the output from the MC3334P chip, pin 7, goes low for the same duration that its pin 5 goes low, thus the spark and dwell timing are both derived from the PIT module and not the HEI board. A 5V supply is taken from the PIT module to power the MC3334P chip, to make it compatible with the PIC. Microprocessor functions Instead of using look-up tables for engine data, the program pre-calculates a set of variables based on the data entered by the user and then stores these into the PIC’s internal EE- Table 1: Resistor Colour Codes ❏ ❏ ❏ ❏ ❏ ❏ No. 6 1 8 4 3 1 60  Silicon Chip Value 10kΩ 2.2kΩ 1.5Ω 330Ω 100Ω 22Ω 4-Band Code (1%) brown black orange brown red red red brown brown green red brown orange orange brown brown brown black brown brown red red black brown 5-Band Code (1%) brown black black red brown red red black brown brown brown green black brown brown orange orange black black brown brown black black black brown red red black gold brown Fig.5: this shows some timing diagrams for a V8, illustrating how the unit delays or retards the ignition timing from a fixed setting. PROM. The PIC uses these variables to generate the appropriate advance settings and therefore does not have to do time-consuming calculations while the motor is running. The PIC’s ignition functions include monitoring the engine RPM, advance timing, dwell pulse width, maximum RPM detect, vacuum pulse width and keeping a constant 45° retard below the minimum RPM point. As these functions are dynamic and are changing all the time, the PIC has to continuously update new data at a very fast rate. It is interesting to note that to keep track of all these functions, the PIC uses about 50 words of code and takes roughly 40µs to update everything. Most of the program memory is taken up by the user interface, while the rest is used for data calculations, the serial display and keypad. It was quite a task to fit all of these functions into a chip that has a mere 1K of ROM. When the PIT module is turned on via the ignition, the PIC will turn the ignition coil on, via the HEI system. If the motor is not started after about six seconds, the coil will be switched off but the PIC will still wait for the motor to be started. This eliminates the possibility of any damage to the coil caused by leaving the ignition on without the motor running. When the motor is cranked over, the PIC will not allow a spark to occur until it has received four trigger pulses. This is to allow the software to stabilise its timing functions. Fig.3 shows a flow diagram of the functions of the PIC microcontroller. The assembled PC board with and without the keypad. The keypad slots into the connector bottom centre of the righthand photograph. Note the IC socket used for the PIC processor – while they make life easy for constructors, in the harsh automotive environment they sometimes give problems. Whether you use a socket or not is up to you. JUNE 1999  61 Fig.6 (left): the component overlay for the PIT module, with keypad removed. Fig.7 (right): actual size artwork for the PC board. Fig.4 shows two possible 2-stage advance characteristics which could be programmed into the module while Fig.5 shows some timing diagrams, illustrating how the unit delays or retards the ignition timing from a fixed setting. Construction The PIT module is easy to build and all the parts except for the micro-switch S1 are installed on the PC board. The component layout is shown in Fig.6. As always, check the PC board for open circuit or bridged tracks before you begin assembly. This done, fit the three wire links followed by the resistors, diodes and sockets for IC1 and IC2, then install the capacitors and other components. Depending on how the unit will be mounted, you may choose to solder the display directly to the PC board or raise it by using an IC socket. The keypad can be connected by using a short length of ribbon cable or it can be connected so that it can easily be removed, by using a 7-pin header plug and socket. Take care with the placement of the ICs, electrolytic capacitors and the LED, as these components are polarized. The keypad can be secured to the PC board by using machine screws and nuts with 10mm spacers. Use nylon washers on the track side of the board to prevent shorts. 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, insert both chips and connect 12V to the PC board terminals on the lower right side of the board. The ground connection is on the outside. When you have done this the centre segment of the display should light. If this test fails, you will need to go over the PC board again and check for faults. Next month we will cover the installation and programming of the module but if you are one of those people who just can’t wait and wants to get started, there is a major step which must be done first: that is to install and check out the HEI system on your car. Get it all going properly, according to the procedure set out in the June 1998 issue. Naturally, this installation will have no connections to the PIT module. When everything has been running with the HEI installed for several weeks, you are ready to proceed to the PIT installation and programming. SC See you next month. Table 2: Capacitor Codes ❏ ❏ ❏ Value 0.1µF .01µF 18pF IEC Code EIA code 100nF   104 10nF   103 18p   180 62  Silicon Chip Again reproduced from the June 1998 SILICON CHIP, this photo shows an internal view of the High Energy Ignition System. Your first step in building the Programmable Timing Module is to get this ignition system working properly.