Fullscreen HTML5Med Res (??MB)HTML4

Last month, we presented part 1 of this 2-part article on the Programmable Ignition Timing module which is teamed up with our High Energy Ignition System, as described in the June 1998 issue. This month we give the details of installa­tion and programming. By ANTHONY NIXON Pt.2: Installation & Programming A S WE NOTED LAST month, do not attempt to hook up the PIT module to the High Energy Ignition (HEI) system until you have had the HEI system running in your car for at least a few weeks. This is good practical advice, as a number of constructors have installed the two systems straight into their cars and then had a torrid time trying to get it all working. So now we assume that you have the HEI installed and work­ing and that the PIT module has been assem60  Silicon Chip bled and the initial checks have been performed. The exact installation of the PIT module will depend on your particular vehicle but it should be somewhere not too obvi­ous. Don’t mount the unit in the engine compartment though, as the parts are not rated for high temperatures. The keypad can be removed from the PC board after program­ming if you wish, as an added security measure. Be sure to run all the wiring in a professional manner, using automo- tive cable and connectors to ensure reliability. HEI connections You will need to make five wire connections from the PIT module to the HEI board, as shown in Fig.8. The +12V supply from the ignition switch is fed to the HEI board, which then supplies 12V and 0V for the PIT module. A +5V connection is taken from the 78L05 (REG1) on the PIT module to the HEI to power the MC3334P chip. Two other wires are used to connect the “Trigger In” from the HEI board and the output from the PIT module to pin 5 of the MC3334P on the HEI board. DO NOT connect a separate ground wire from the PIT module to the vehicle chassis. If the ground wire from the HEI board goes open-circuit, the high coil currents will try to flow through the small PC board tracks on the PIT module, possibly causing them to burn off and damage the ICs. Vacuum switch Fig.9 shows the mounting details for microswitch S1. It is mounted on a rightangle bracket which is attached to the vacuum actuator. The arm of the microswitch sits in a slot cut into the vacuum actuator and in the absence of vacuum, is normal­ly held down. When vacuum is present, the actuator moves upward and the microswitch arm releases. Be sure to connect the leads to the microswitch exactly as shown; ie, the lead from pin 3 of the PIC goes to the contact marked “NO”). As mentioned previously, the advance plate in the distributor must be clamped with the weights in the outward position. If you do not wish to use the electronic vacuum ad­vance, then you can leave the original setup as is and leave the vacuum advance input (RA4) disconnected. Another use for the vacuum advance input is to interface it to the Knock Sensor project, as published in the April 1996 issue of SILICON CHIP. The filtered output from the knock sensor is fed to an LM311 comparator. When this voltage goes higher than that preset on the inverting input pin 3, the output at pin 7 will go high. When the PIC detects this high it will retard the ignition by an amount set This view shows the assembled PC board without the keypad. The keypad plugs into the connector located near the bottom edge. by the user. Fig.10 shows the circuit. In effect, it works in the opposite manner to which it was intended. As the output of the LM311 is open-collector, it provides compatibility between the 8V circuitry of the Knock Sensor and the 5V supply of the PIT module. Note: this circuit arrangement has not been tested on a vehicle. Rotor contact modification Normal ignition advance in a conventional distributor is achieved with a mechanical setup using bob weights and springs and the amount of advance depends on the throttle opening and engine RPM. The changes in advance also change the position at which the rotor button passes by the spark lead contacts in the rotor cap when a spark is produced. To cater for this, the end of the rotor button contact is usually flared so that it is able to conduct the high voltage to the spark plug contacts over the full advance range. Fig.11 shows what is required. The PIT module has 45° of advance JULY 1999  61 Fig.8: use this diagram when connecting the PIT module to the HEI system. available. This means that your rotor button may need to be modified so that it will stay in contact with the spark lead connections over this advance range. Remember that we are talking about 45° of crank advance. This translates into 22.5° of distributor advance because the distributor cam turns at half the speed of the crankshaft. Therefore the flared end of the rotor button must be elon­gated to function over 22.5° and possibly more, if the 62  Silicon Chip original vacuum advance is left connected. If the extension is too narrow or too wide, then a spark might be missed or worse, the spark may “jump” to the wrong spark contact, causing misfir­ing. Fine tuning this part of the project may require a little trial and error to get it right. Initial timing setup When the engine is first started, the PIT module retards the ignition by 45 crank degrees (22.5 distributor degrees) and stays constant at this value until the engine RPM reaches the user programmed MIN RPM value. The timing will then begin to advance at the programmed rate. Before attempting to modify the distributor or change its position, make a note or mark the position it is currently in. In last month’s article, it was mentioned that the distributor is modified by wiring its advance weights in the fully out position and the vacuum advance plate is clamped Fig.9: the vacuum actuator is modified to operate a microswitch. At low vacuum, the microswitch arm is held down. Conversely, when manifold vacuum is high (ie, at light engine loads), the microswitch arm is released. so that it cannot move. This will give a certain amount of advance from your base set­ting. Use a protractor to find out how much “distributor” advance this is and sub­tract it from 22.5. If the answer is positive, advance the dis­ tributor from its original position by this amount. Then when the engine starts, the PIC will retard the timing back to the origi­nal base setting and begin advancing it again as the RPM rises. If the result was negative, the advance value that your engine gives is greater than the advance range that this system can cater for and may not work. When the ignition is timed (using a timing light), the vacuum advance must be disabled. This is accomplished by removing and blocking off the vacuum hose so that it has no effect on the vacuum switch. Static timing To time the engine with the engine stopped (ie, static timing), 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 PIC detects that the points are closed. This method will not work with a reluctor pickup. Note that because the LED drive signal frequency is propor­tional to the engine RPM, this signal can be used to drive a tachometer. Programming There are nine parameters that must be programmed into the PIC to make up each data set. Every parameter, as well as the correct number of digits for these parameters, must be entered. The PIC will monitor the digit entry and display each numerical keypress. After the last digit of the last parameter has been entered, only the centre segment of the display will be illumi­nated. If this segment fails to light, then you have not entered enough data. If the segment lights before you have finished, then you are trying to enter too much data. In Table 1: Data Set Contents Parameter Digits Example Mi n RPM 4 0800 Mi d RPM 4 3000 Mi d Advance 2 20 Max RPM 4 500 0 Max Advance 2 30 D w el l 2 20 Vacuum Advance 2 10 C yli nders 2 06 Security Code 2 99 either of these two cases, you must enter the complete set of data again. You will notice that the data for the MIN RPM and Cylinders both have leading zeros. The MIN RPM value is allocated four digits, so four digits must be entered. Similarly, the Cylinders value is allocated two digits, so two digits must be entered. You cannot enter an RPM value that is lower than a previous RPM value. For example, MID RPM cannot be lower than the MIN RPM value of 0800. The PIC has two internal advance ranges from 30 to 300 RPM and then from 300 RPM to the MIN RPM value that you specify and for this RPM range the timing is fully retarded. The MAX Advance value can be greater than, equal to, or lower than the MID Advance value. This allows the second stage advance to have a retarding effect, if needed, rather than con­tinuing to advance the timing until MAX RPM is reached. The negative advance feature is common to both data sets, which means that if you want a negative advance setting for one set, you must also have a negative advance setting for the other. If one is positive and the other negative, then the positive data set will malfunction (see the note at the end of this article). The absolute minimum dwell width that the software will generate JULY 1999  63 Fig.10: this circuit could be used to enable the PIT module to operate in conjunction with the Knock Sensor featured in the April 1996 issue of SILICON CHIP. Fig.11: the trailing end of the rotor button contact needs to be extended and the leading edge trimmed to cope with the modified operation of the distributor. Note that fine tuning this part of the project may require some trial and error to get it right. 64  Silicon Chip is 1ms. In this system, this is the time that the coil is OFF. If you enter a “00” value for the Dwell, then a constant 1ms 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 may be reached when the dwell width is calculated to be less than 1ms. When the PIC detects this, it sets the minimum to 1ms. The dwell angle from any input device has no effect on the system dwell times, however it is good practice to set the points nor­mally, as specified by the manufacturer. The PIC will debounce the points signal, whether points or electronic sensors are used. If you do not wish to use the electronic vacuum advance then enter “00” for that parameter. After you enter a security number, you must remember it. If you forget, you will not be able to gain access to the system unless you tediously go through the 99 code combinations, one by one. If you do not want to use a security code then just enter “00”. You must press the “*” key after entering all the data as this tells the PIC to run the calculations and store the results into the EEPROM. If you do not do this before removing power, the new data set will be lost. Due to memory restrictions, the PIC does not do any error checking on entered data. The Cylinder value and the Security Code are common to both data sets. If you change the cylinder value in one data set, then you must re-enter the other data set with the new cylinder value as well and run the calculations again. For example, if you entered 6 cylinders for data set one, and afterwards you enter 8 cylinders for data set two, then the calculations will be wrong in data set 1 because they were based on 6 cylinders. You only have 45° of advance to “play” with, so any data you enter that goes outside this range may result in erratic operation. The software can handle an advance value plus a dwell value greater than 45° but as soon as the points open, the PIC will “chop” the last timing sequence off in favour of the new one when it becomes necessary for the coil to be switched off. This may only result in a shorter dwell time but it may also result in misfiring. The software is trying to cater for a wide range of operating conditions, but it may not be able to operate with values that are too far out of the ordinary. Operational modes There are two modes of operation for this system: Data Entry Mode and Engine Run Mode. If you look at the system flow chart featured in last month’s article, you should be able to follow how everything works. If there is no data set stored in EEPROM for the current level, then the system will power up in Data Entry Mode and the centre display segment will be lit. If there is data, then the system will power up in Engine Run Mode. Data Entry Mode The PIC will be waiting for a keypress to select a particu­lar programming function. These are the ones that are available: Function Key Read RAM   3 Read EEPROM   4 Enter New Data   5 Clear Display   6 Change Data Set   7 Display Data Set   8 Calculate/Store data   * Exit   # • Read RAM - Key 3: After pressing this key, repeatedly pushing the “*” key will display the data stored in RAM. Each parameter is separated by a “-” character. If there is no data in RAM then an error condition will be displayed. Press key “#” to exit. • Read EEPROM - Key 4: This transfers the current data set from EEPROM to RAM. Any previous RAM contents will be lost but the EEPROM contents will remain unchanged. After pressing this key, repeatedly pushing the “*” key will display the data now stored in RAM. Each parameter is separated by a “-” character. If there is no data in the EEPROM then an error condition will be displayed. Press key “#” to exit. • Enter New Data - Key 5: After pressing this button, a “0” will be displayed and you can then enter a new data set. From the example in Table 1, you would enter the data as follows: 080030002050003020100699 After the last “9” key is pressed, the display will show “-” to indicate that all data has been entered. Because all timing is now controlled electronically, the advance plate inside the distributor must be securely clamped in the fully-advanced position and its advance weights wired in the fully out position. In effect, the Programmable Ignition Timing Module retards the timing from the preset maximum to give the correct value according to engine speed and load. If a mistake is made while entering the data set, you can press the “#” key to abort. Press key “5” again to restart the data entry process. • Clear Display - Key 6: “-” is displayed. • Change Data Set - Key 7: This key alternates between the two data sets available. When data set one is selected, “1” is displayed. Similarly, when data set two is selected, “2” is displayed. You can alter­nate between the two sets even though they do not have data stored, but you will not be able to start the engine if the selected set does not have valid data. This key can also be used while the engine is running but only if both sets have valid data. • Display Data Set - Key 8: This key displays the currently select­ed data set. • Calculate/Store Data - Key *: When this key is pressed, a set of engine operating parameters will be calculated according to the data that was entered. The results, along with the user data in RAM will be stored into EEPROM so that they are available each time the ignition is turned on. If there is no valid data in RAM an error message will be displayed. • Exit - Key #: Pressing this key terminates functions 3 and 4. If the system is in Data Entry Mode waiting for a function to be select­ed and there is data available in the current set, then the system will go into Engine Run Mode and wait for the engine to start. If the current data set is not valid then the system will stay in Data Entry Mode. The error condition that is displayed is similar to a “?” character. Quick programming review (1) Turn Power on. (2) Select data set – Key “7” (3) Begin data entry – Key “5” (4) Key in data – eg, 080030002050003020100699 (5) “-” will be displayed (6) Calculate/Store data – Key “*” (7) Either enter other data set, back to step 2, or press key “#” to allow engine start. Engine Run Mode If the “#” key was pressed while in Data Entry Mode with a valid data set available, then the current data set will be displayed, and the system will wait for the engine to start. If the system is powered up and JULY 1999  65 Reprogramming Existing Chips Any new software can be reprogrammed into your existing chips if they are sent to the author with a $5.00 fee for postage, etc. There is one small problem here. Originally the software was written for the PIC 16C84 which only has 36 bytes of RAM. These chips are now obsolete and were replaced by the newer 16F84s which have 68 bytes of RAM. The latest software needs 38 bytes of RAM to operate so the 16C84s cannot be reprogrammed. Programmed 16F84s are available and are still at the original $27 which includes postage & packing. Chips can be returned for reprogramming or ordered from: Anthony Nixon, 8 Westminster Court, Somerville Vic 3912. If you return the chip, please make sure it is properly packaged to prevent mechanical as well as static damage, as no responsibility can be taken by the author if a chip is damaged in transit. There is some basic information about the ignition module as well as an email link at http://www.picnpoke.com the current data set is valid, then two things can happen. If there is no Security Number then the software will wait for the engine to start and the display will show the data set that is being used. If there is a Security Number then the display will be blank and you must type in the exact two-digit code to unlock the controller. If the wrong code is entered, then the software will do nothing at all, so you must turn the power off and start again. If the correct code is entered, the software t bu d e l i o s p o h S E! C I R P F L HA will wait for the engine to start and the display will show the data set that is being used. While the PIC is waiting for the engine to start, you can go into Data Entry Mode by pressing key “9”. You cannot do this after the engine starts. When the engine is running, you can alternate between data sets by pressing key “7”. There must be valid data in both sets for this to happen. Problems with installation The PIC is a pretty robust little chip but it is sensitive to static electricity and also to electromagnetic interference (EMI), so when handling the chip try not to touch the pins. Do not be tempted to try the project out on the bench if it is connected to the HEI module and a coil and spark plug. The open spark will cause the PIC to run erratically due to the EMI produced and will fool you into thinking something is wrong. Keep all of the PIT module wiring away from the ignition coil as the electrical noise produced here may interfere with the PIC. Negative advance addendum Nearly all of the PICs that have been supplied in the past with the negative advance feature have a small white dot on the top surface of the chip. When using these chips, both data sets must be programmed for either positive or negative advance, not mixed, or the positive data set will treat the data as being negative and give improper operation. There was a great deal of time taken to scrounge up enough memory to change this so that this restriction no longer applies. Either set can now be positive or negative. The PICs programmed with this software will have a coloured dot instead of white placed SC on the top surface of the chip. 14 Model Railway Projects THE PROJECTS: LED Flasher; Railpower Walkaround Throttle; SteamSound Simulator; Diesel Sound Generator; Fluorescent Light Simulator; IR Remote Controlled Throttle; Track Tester; Single Chip Sound Recorder; Three Simple Projects (Train Controller, Traffic Lights Simulator & Points Controller); Level Crossing Detector; Sound & Lights For Level Crossings; Diesel Sound Simulator. Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop-soiled or have minor cover blemishes. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) This book will not be reprinted Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 66  Silicon Chip $