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Universal High-Energy Electronic Ignition Sys This new universal high-energy electronic ignition system completely supersedes our previous transistor-ignition designs. It works with a variety of input triggers and employs a high-temperature microcontroller to control the switching transistor and sense the trigger signal. T HIS NEW ELECTRONIC ignition system will not only will work with traditional points but will also happily function with any type of trigger signal – including those provided by factory and after-market reluctor, optical and Hall Effect distributors. It will even interface with an ECU ignition output trigger, making it a universal fit for all single coil cars, motorcycles and go-karts. It’s the ideal upgrade for an old points ignition 30  Silicon Chip system or it can be used to replace a defective factory ignition module – for as little as one-fifth of the price. This all-new design also compensates for lower battery voltages during cranking, features reduced coil heating, has adjustable intelligent dwell and incorporates a theft-prevention ignition disable. Ignition system designs Charles F. Kettering was an inven- tor extraordinaire. Not only did he develop the electric starter motor but in about 1910 he invented the first really effective automotive ignition system. The standard Kettering ignition circuit is shown in Fig.1. As this diagram shows, a battery is connected to a primary winding of the ignition coil, with the current interrupted by the distributor points. The distributor points are opened and closed by a cam on the shaft of the distributor. The lobes of the cam are arranged so that the points open at the start of each cylinder’s firing stroke. When the distributor points are closed, current builds up in the primary of the ignition coil and produces a magnetic flux in the iron core. The time that the points are closed is called the “dwell period”, while the magnetic flux is the energy stored in the coil. When the points open, the coil current is suddenly stopped and the magsiliconchip.com.au Pt.1: By JOHN CLARKE stem netic field collapses. This produces a sharp voltage spike across the coil’s primary winding. Since the ignition coil is also a transformer, this large voltage spike is stepped up to appear across the secondary winding. The secondary’s voltage is fed to the spark plugs via the rotating contact in the distributor and the spark plug leads. The capacitor (sometimes known in automotive circles as a condenser) in parallel with the points reduces arcing across the opening points. It achieves this because at the moment of the points opening, the capacitor appears as a short circuit. There is therefore a lack of voltage across the opening points, preventing arcing. The capacitor also forms a parallel resonant circuit with the coil primary, maximising the energy developed in the primary. Without the capacitor in a points ignition system, the spark will be very weak. siliconchip.com.au Fig.1: a Kettering ignition system is a very simple design. A battery is connected to a primary winding of the ignition coil, with the current interrupted by the distributor points. When the distributor points are closed, current builds up in the primary of the ignition coil and produces a magnetic flux in the iron core. When the points open, the coil current is cut off and the magnetic field collapses. This produces a sharp voltage spike across the coil’s primary winding which is stepped up to appear across the secondary. The secondary’s voltage is fed to the spark plugs via the rotating contact in the distributor and the spark plug leads. The capacitor reduces arcing across the opening points. On most cars of the last 20 years, the points have been replaced with an electronic switch (usually a reluctor or Hall Effect sensor) and a power transistor. This system remained in place until the late 1950s, when a ballast resistor was added. This resistor was placed in series with the coil primary so that the voltage applied to the coil did not exceed 7V. During cranking when the battery voltage was low, the ballast resistor was switched out so that full battery voltage was applied to the coil, thus giving improved starting. The next development – starting in the late 1970s – added electronic switching of the coil. By using the points only as a switch input for the electronic system, the current load carried by the points was reduced. This resulted in much less pitting and wear of the contacts. However, over time, the rubbing block of the points still wears out and so fully electronic systems were introduced that replaced the points with a contactless sensor. These systems use reluctor, optical or Hall Effect sensors positioned inside the distributor to trigger the electronic switching. Main Features • Operates from points, reluctor, Hall Effect and optical triggers, or 5V signal from engine management computer • • • • • • • • • 5-15V negative earth operation Selectable dwell period Coil switches off whenever engine is not turning Dwell extension with low battery voltage Minimum spark duration of 1ms Two points debounce periods Special operation for poorly operating points Anti-theft ignition disable switch option Optional inverted trigger signal operation December 2005  31 Fig.2: the circuit is based on PIC microcontroller IC1. It accepts the trigger input signal, calculates the dwell and controls high-power Darlington transistor Q1 via transistor Q2. Q3 provides the tachometer drive signal. Note that in these approaches, the ignition system remains a stand-alone device; fuel is provided by a completely separate carburettor or fuel injection system. The development in the 1980s of engine management integrated the fuel and ignition systems. The position sensor acted as an input to the Electronic Control Unit (ECU), with the ECU outputting a signal to a dedicated ignition module that switched the coil. High voltage spark distribution in these single coil systems continued to be achieved by a distributor. Finally, the distributor has now been replaced by individual coils for each cylinder (or in some cases, double-ended coils for cylinder pairs), where each coil has its own switching electronics and is fired by direct signal from the ECU. The electronic ignition system presented here is suitable for upgrading 32  Silicon Chip all the described systems except the last: it will not work with multi-coil cars (well, not without buying a bunch of ignition kits, anyway!). Input triggers The way in which points work is easy enough to understand but what’s all this about reluctor, optical and Hall Effect sensors? • Reluctor: a reluctor trigger comprises a coil wound around an iron core. A ring magnet with small externally protruding sections (teeth) is installed on the distributor shaft. As each tooth of the magnet passes the sensor, a voltage is developed in the coil. These voltage spikes provide the timing signal. Incidentally, in place of the reluctor, a magneto signal can be used as a suitable trigger signal for this project. • Optical: an optical trigger comprises a LED and a phototransistor or photo diode. The pair is incorporated within a package that allows the light from the LED to impinge on the photodetector. To switch the photodetector on and off, an opaque vane passes between the LED and its sensor. In addition to factory optical systems, this ignition caters for commercial optical ignition triggers such as those from Lumenition, Piranha and Crane. • Hall Effect: a Hall Effect trigger is a semiconductor device that switches its output on or off, depending on the presence or absence of a magnetic field. Generally, the magnet is included within the sensor package and so the sensor is easily triggered by passing an iron vane through the provided gap. The Hall Effect unit triggers when the iron vane is removed from the gap. • ECU: as described above, in singlecoil cars with engine management, the ECU signals the ignition module when siliconchip.com.au to switch off current to the coil. This signal is generally a 5V square wave. New design features The starting point for this design was the High Energy Ignition published in the May and June 1998 issues of SILICON CHIP. While that design worked well, the MC3334P ignition IC used in the project is now obsolete. Fortunately, the availability of cheap programmable microcontrollers solves that problem and also allows us to add new features without substantially increasing the complexity or cost. • Variable Dwell: in the previous design, the ignition coil was charged for virtually the whole time, with only a 1ms break when it was called upon to fire the coil. This was done to ensure that the coil was as fully charged as possible. However, this caused a lot of heat generation in both the coil and switching transistor. This is because after the coil becomes fully charged, the only restrictions to current flow are the series resistance of the coil and the ballast resistor (if fitted). In our new design, the coil charges for only the correct dwell period for the specific coil. In practice, the coil is switched on just before firing, the selected dwell time ensuring that the coil is fully charged but without the consumption of any more power than required. If the engine RPM becomes so high that the dwell period cannot fit within successive firings of the coil, the dwell period is reduced but with the firing period fixed at a minimum of 1ms. This 1ms minimum allows sufficient time for the coil to deliver a healthy spark. The dwell can be set from 1-33ms in 1ms steps, with most coils typically requiring at least 4ms dwell. To compensate for the longer charging period required for the coil with a lower supply voltage, the dwell time is automatically extended when the battery voltage falls below 12V. This helps maintain spark energy when starting the engine. Another important feature of this unit is that the coil is not energised when the ignition is switched on. It charges only after the engine has begun to crank. This feature prevents the coil from overheating when the ignition is switched on but the engine is not started. In addition, if the engine stops turning with the ignition still switched siliconchip.com.au Specifications Dwell Settings: 1-33ms in 1ms steps or an input dependent selection Spark Duration: a minimum of 1ms Dwell Extension With Voltage: progressively increases from 2x at below 12V through to 4x at 7.2V supply. Debounce Period: 0.5ms or 2ms selectable Timeout Delay: coil switched off after about 1s with engine stopped Maximum RPM For 1ms Dwell & 1ms Spark: 15,000 RPM for 4-cylinder, 10,000 RPM for 6-cylinder and 7500 RPM for 8-cylinder engines (4-stroke) Maximum RPM Before Selected Dwell Begins To Reduce: • For 5ms dwell – 5000 RPM for a 4-cylinder engine, 3300 RPM for a 6-cylinder engine, 2500 RPM for an 8-cylinder engine For 10ms dwell – 2727 RPM for a 4-cylinder engine, 1818 RPM for a • 6-cylinder engine, 1363 RPM for an 8-cylinder engine • For 15ms dwell – 1875 RPM for a 4-cylinder engine, 1250 RPM for a 6-cylinder engine, 937.5 RPM for an 8-cylinder engine on, the coil is turned off after about one second. • Points Debounce: points debounce is needed because points tend not to open or close cleanly. When closing, points can bounce back open, just as a hammer does when hitting a steel plate, and this can cause a series of rapid openings and closings. When opening, the points can also bounce as the distributor cam wobbles, because of slight play in the distributor shaft. By setting the minimum spark duration at 1ms, the coil will fire cleanly as the points first open. This provides the full spark duration and by this time the coil will have discharged. However, if the coil is then allowed to charge up before the points close again, there can be a second spark produced if the points bounce upon closure. This second spark can produce ignition in one of the engine cylinders at the wrong time. The solution for this is to provide a points debounce period so that when the points first close, subsequent openings can be ignored. However, there is a limit to the length of this debounce period. If it is made too long, then the upper RPM of the engine can be severely limited as the time between firing points becomes the same as the debounce period. For severe points bounce problems, it is best to start charging the coil only after the points close, so that any points bounce will not produce a spark. To solve these problems, we have provided a “points” selection mode. However, in this mode, some of the advanced features of the system are lost – dwell time becomes fixed, for example. In this mode, the firing duration and dwell are set by the time that the points are open and closed, respectively. This setting should be selected when using points that produce erratic firing using the normal setting. A 2ms debounce period can also be selected for points rather than the standard 0.5ms for other trigger inputs. • Voltage Level Sense: because of the large number of triggers that can be used, there is an option to change the voltage level sense that determines the firing point for ignition. For points, the firing point is always when the points just open, so in this case the voltage goes positive from 0V to 12V. For other sensors, the voltage sense may be different. For example with the Hall Effect or optical triggers, it depends on whether the ignition firing point occurs when the vane enters the sensor or leaves the sensor. So at the firing point, the voltage could be going from 0V to a more positive voltage, or from the positive voltage to 0V. A simple jumper change selects the required sense. Circuit description The circuit for the Electronic Ignition is based around high-temperature December 2005  33 Par t s Lis t – Ignition System 1 PC board, code 05112051, 102 x 81mm 1 diecast aluminium case, 119 x 93 x 57mm 2 cordgrip grommets 1 transistor insulating bush 1 T0-218 insulating washer rated at 3kV 1 8MHz crystal (X1) 1 18-pin DIL IC socket 3 3-way pin headers 3 shorting links 3 crimp eyelets 4 9mm tapped standoffs 4 M3 x 15mm screws 2 M3 x 9mm screws 6 M3 star washers 10 PC stakes 1 2m length red automotive wire 1 2m length black automotive wire 1 2m length green automotive wire 1 100mm length of 0.7mm tinned copper wire 1 5kW horizontal trimpot (VR1) Semiconductors 1 PIC16F88-E/P microcontroller programmed with ignition.hex 1 MJH10012, BU941P TO-218 high-voltage Darlington transistor (Q1) 2 BC337 NPN transistors (Q2,Q3) 1 LM2940CT-5 low-dropout 5V regulator (REG1) 4 75V 3W zener diodes (ZD1-ZD4) Capacitors 3 100mF 16V PC electrolytic 1 10mF 16V PC electrolytic 1 100nF MKT polyester 1 10nF MKT polyester 1 1nF MKT polyester 2 33pF ceramic Resistors (0.25W 1%) 1 100kW 1 1.8kW 2 47kW 1 470W 2 2.2kW 1 100W 5W Points version 1 100W 5W resistor Reluctor Version 1 BC337 NPN transistor (Q4) 1 2.2nF MKT polyester capacitor 1 470pF ceramic capacitor 1 100kW top-adjust multi-turn trimpot (VR2) 1 47kW 0.25W 1% resistor 2 10kW 0.25W 1% resistor 1 1kW 0.25W 1% resistor 1 PC stake Hall Effect Version 1 Hall Effect sensor (Jaycar ZD1900) or Lumenition module 1 rotating vane using a 15W power potentiometer backing (eg, Jaycar RP-3975 – not required for Lumenition module) 1 small quantity of high-temp­ erature epoxy (eg, JB Weld Epoxy Steel Resin) 1 1kW 0.25W 1% resistor 1 100W 0.25W 1% resistor 2 PC stakes Optical Pickup Version 1 optical pickup (Piranha, Crane, etc) 1 22kW 0.25W 1% resistor 1 120W 0.25W 1% resistor 2 PC stakes Miscellaneous Angle brackets for mounting, automotive connectors, self-tapping screws etc. Note: the programming code (ignition.hex) for the PIC16F88-E/P microprocessor featured in this project will not be released or be made available on our website. Authorised kitsellers will supply programmed micros as part of their kits. For people who do not wish to build the project from a kit, programmed micros will be available from SILICON CHIP for $25.00 including postage anywhere within Australia, or $30.00 by airmail elsewhere. microcontroller IC1 (a PIC16F88-E/P) which processes the signal from the ignition trigger – see Fig.2. An output on the microcontroller drives transistor Q2 and this controls the action of the main switching transistor Q1. 34  Silicon Chip Transistor Q1 is a Darlington transistor specifically made for ignition systems. It is capable of handling currents of over 10A when it is switched on and voltages exceeding 400V when it is switched off. Four 75V zener diodes Spark Timing The electronic ignition system presented here does not alter spark timing. Irrespective of whether the required variation in timing is provided by a weights and vacuum advance/retard system or electronically by the ECU, the original timing will be retained when the electronic ignition system is installed. In a future issue we intend presenting a development of this project that will allow ignition timing to be altered. That project will allow the existing timing to be fully mapped on the basis of engine RPM and inlet manifold pressure. Firing Spacing Some rare engines have an uneven length of time between cylinder plug firings. This can be seen by an uneven spacing of the cam lobes within the distributor, or an uneven spacing in the electronic trigger (eg, the slots in a Hall Effect vane). This electronic ignition system is not suitable for such applications except when set in points mode. (ZD1-ZD4) are connected in series to protect the transistor from excess voltages by clamping the collector voltage at 300V. An ignition inhibit link (LK4) is connected in series with transistor Q1’s base drive. When this connection is open, the transistor does not switch on and so the ignition is disabled. This allows a hidden switch to be added, to enable and disable the ignition to protect the car from theft. Base drive for Q1 is via a 100W 5W wirewound resistor from the 12V supply. The current through this resistor is diverted from Q1’s base when transistor Q2 is switched on. When Q2 is off, Q1 is switched on and the ignition coil is charged (ie, current flows through the primary). As soon as Q2 switches on, Q1 is switched off and the coil’s magnetic flux collapses so as to develop a high voltage in the secondary to drive the spark plug. Transistor Q2 is driven via a 470W resistor from the RB3 output (pin 9) of IC1. siliconchip.com.au Fig.3: the six input trigger circuits: (a) points triggering; (b) Hall effect (and Lumenition) triggering; (c) triggering from an engine management module; (d) reluctor pickup; (e) Crane optical pickup; and (f) Piranha optical pickup. IC1 accepts its timing signal at the RB0 input (pin 6) and drives the RB3 output accordingly. The RB0 input is protected from excess voltages by the 2.2kW resistor in series with this input. The protection resistor prevents excessive current flow in the clamping diodes that are internal to IC1. Clamping occurs when the voltage goes below 0V or if it goes above the 5V supply (ie, clamping to -0.6V or +5.6V). The 1nF capacitor at the RB0 input shunts transient voltages and higher frequency signals, preventing false timing signals. The three inputs at RA1, RA4 and RA5 (pins 18, 3 & 5) are for the linking options. Link LK1 selects whether the firing edge for the RB0 input is for a positive going voltage (standard selection) or for a falling voltage (inverted selection); link LK2 selects either the standard 0.5ms debounce period or the 2ms period; and Link LK3 selects normal or points operation. There are two voltage inputs –AN3 (pin 1) and AN2 (pin 2). The AN3 input is used to monitor the car battery voltage via the 100kW and 47kW voltage divider. It is included to allow the dwell time to be automatically increased at voltages below 12V. Trimpot VR1 applies between 0V and 5V to the AN2 input to provide siliconchip.com.au a means of setting the dwell time. A 5V setting gives a 1ms dwell period, while 0V selects the 33ms maximum dwell, with other settings between these extremes setting the dwell in 1ms steps. Both the AN2 and AN3 inputs are decoupled using a capacitor to ground to filter transient voltages. Transistor Q3 provides a tachometer output and it is driven from the trigger input which also drives pin 6 (RBO) of IC1. Q3’s collector is pulled up to 12V with a 2.2kW resistor when the transistor is off. The output at Q3’s collector can be used to drive most tachometers. An impulse tachometer (now very rare) requires a different connection and should operate when connected to the coil negative. As set by crystal X1, IC1 runs at 8MHz. Its supply is decoupled with a 100nF capacitor for high frequencies and a 100mF capacitor for the lower frequencies. Power for the circuit is derived from the ignition switch. This 12V supply is also directly used for other parts of the circuit. For example, it is used for the points trigger circuit and the 100W base resistor for Q1. The supply is regulated to 5V using 3-terminal regulator REG1. This is a low-dropout device that continues to deliver 5V even when its input is very close to 5V. This is useful in our application, as we want a regulated 5V supply to be maintained even when starting, when the voltage on the car battery can drop well below 12V. The regulator is also protected from transients with internal protection clamping. The 100mF capacitors provide supply decoupling. Trigger inputs The Electronic Ignition is configured for the appropriate trigger input during construction. The six possible input circuits are shown in Fig.3. The points input shown in Fig.3(a) comprises a 100W 5W wirewound resistor connected to the 12V supply. The resistor provides a “wetting” current for the points to ensure there is a good contact between the two mating faces when they are closed. This wetting current is sufficient to keep the contacts clean – burning off oil resides, for example – but not so high so as to damage them. The Hall Effect input at Fig.3(b) uses a 100W supply resistor to the 12V rail to feed the Hall sensor. This resistor limits current into the unit should a transient on the supply go above its internal clamping diode level. The 1kW resistor on the output pulls up the output voltage to 5V when the inDecember 2005  35 Fig.4: this oscilloscope view shows a reluctor signal (top) and the output of the ignition coil, as measured at the collector of Q1 (bottom). The reluctor signal has a larger voltage excursion than other trigger sensors and the negative-going edge triggers the firing of the coil. The primary voltage of the coil (lower trace) is clamped at around 332V by the four series 75V zener diodes. Fig.5: the yellow trace at top shows the reluctor signal, while the lower trace (blue) shows the base switching signal to transistor Q1. The coil fires each time the base voltage goes to ground. Note that the period for which the base signal is positive (ie, 6ms) is the dwell time and this is the charge period for the coil (ie, when energy is being stored in the magnetic circuit of the coil). Fig.6: at top is the signal at the trigger input of the circuit ie, the signal that is monitored by the RB0 input of IC1 via the 2.2kW resistor. This signal is typical of a points, Hall Effect and optical triggering. The lower trace is the base drive to transistor Q1. This shows the 6ms dwell occurring just before firing. Fig.7: the top trace (in yellow) is a high RPM signal (in this case, 6000 RPM for a 4-cylinder 4-stroke engine). The lower trace (in blue) shows the resulting switching signal fed to the coil. Note how the dwell is now 3.98ms instead of the standard 6ms, while the spark duration is fixed at 1ms. What About The Multi Spark CDI? Considering that this project supersedes all previous versions of our very popular High Energy Ignition (HEI) system, readers may be wondering about the status of the Multi-Spark Capacitor Discharge Ignition system which was featured in the September 1997 issue of SILICON CHIP. The good news is that this project is still valid for 2-stroke engines, high performance 4-stroke engines and old vehicles, particularly those with high compression motors. The kit is still available from Dick Smith Electronics (Cat. K-3307) at $148.00. The DSE kit is supplied with all specified components and hardware, including a diecast box to house the project. Kits are available only on special order through the DSE web address at www.dse.com.au or through their mail-order Sales Department (phone 1300 366 644 toll-free Australia only). 36  Silicon Chip ternal open-collector transistor is off. The voltage is at 0V when the internal transistor is on. The same circuit can be used for the Lumenition optical module. The engine management input circuit is shown in Fig.3(c) and is quite simple – its 5V signal connects to the trigger section of the main circuit in Fig.2. Reluctor sensors produce an AC signal and so require a more complex input circuit – see Fig.3(d). In this case, transistor Q4 switches on or off, depending on whether the reluctor voltage is positive or negative. siliconchip.com.au Fig.8: this shows the points mode where the input points signal at top is followed by the output signal (lower trace). The debounce period is set at 2ms, as shown by the 2ms pulses that follow the main pulses. Initially with no reluctor voltage, transistor Q4 is switched on via current through VR2 and the 47kW resistor. The voltage applied to Q4’s base is dependent on the 10kW resistor connecting to the top of the reluctor coil and the internal resistance of the reluctor. VR2 is included to provide for a wide range of reluctor types. Some reluctors have a relatively low resistance, while others have a higher resistance. In practice, VR2 is adjusted so that Q4 is just switched on when there is no signal from the reluctor. The 10kW resistor provides a load for the reluctor, while the 470pF capacitor filters any RF or hash signal that may have been induced. The 2.2nF capacitor ensures that Q4 quickly switches off when the reluctor signal goes negative. Optical pickup circuits are provided for two different types of modules. One is for a module that has a common 0V supply connection [eg, Crane – Fig.3(e)] and the other for a module that has a common positive supply [eg, Piranha (Fig.3(f)]. In each case, current for the LED is supplied via a 120W resistor and the photodiode and a 22kW resistor are connected in series with the 5V supply. Next month, we will give the full construction details and describe the installation. We’ll also describe how to convert a distributor from points to SC Hall effect trigger operation. Talk about a generation gap. The new Tektronix AFG3000 Series signal generators vs. the competition. c 2005 Tektronix, Inc. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. TEKTRONIX and the Tektronix logo are registered trademarks of Tektronix, Inc. *Tektronix MSRP subject to change without notice. Starting from around $2600+GST. * Unlike the subtle advancements offered in arbitrary/function generators of past decades, our powerful and broad line of arbitrary/function generators delivers serious advantages. The large display confirms your settings at a glance. Sine waveforms reach as high as 240 MHz. You get a front-loading USB port, twochannel capability, and a remarkably intuitive GUI. Visit www.tek.com/generation_gap to see the next generation of signal generation. The Next Generation. http://www.tektronix.com/4130 Enabling Innovation Tektronix Authorized Distributor N e w Tek Instruments Pty Ltd Here is a preview of the assembled PC board (Reluctor version shown). The full assembly details are in Pt.2 next month. siliconchip.com.au Address: 3 Byfield Street, North Ryde NSW 2113 Telephone: (02)9888-0100 Email: info<at>newtekinstruments.com December 2005  37