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Yes this is the idea and it is working with the old circuit but not in a save way as we have HV spark running over a small gap 1-2mm which also create interference ,
Yes and the reason is I rebuild Classic English cars Aston Martin,Jaguar and most of the times when I buy a car the engine is broken or not running which is no problem mechanical parts I can get in the UK however the Lucas ECU are discontinued for at least 15 years and lucas also does not make ECU in general any more,It is necessary for me to test the ECU before I buy the car and this bench test setup works prefect.
I am not an electrical person so for my learning curve I wanted so see how the signal looks ,I thought I might see some ripple or irregularities ,just to experiment and learn
The current circuit is only the 200V generator circuit WHONOES said that once I have this working he will help me to do the Pulse switching circuit
This testing of the ECU is ideal as when we have the Ignition /Coil signal the ECU goes live and I can monitor the actual injection time and also by varying the Engine and Air temperature and the Throttle position signal(simulated by Variable resistors of corresponding value) I can measure the actual injection time and also see that the ECU reacts to the various operating conditions and OP points.
Hope this help to understand why and for what I am trying to do this circuits
Thank you again to all for your inputs and comments
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Surely 600Hz is two times to many. You seem to have assumed that for a 12 cylinder engine you get 12 bangs per revolution but as the engine is a 4 stroke you only get 6 bangs per rev' thus just 300Hz at 6000RPM.
Hi WHONOES
I measure between the input pin of the ECU and the Pin on the Internal IC / Prosessor 120 KOhm with a DMM ,Yes you are correct the distributor runs at 1/2 engine speed that is 12 pulses in an engine cycle (720°) effectively 6 bangs per ref
I am curious why is the input impedance so important ?
I measure between the input pin of the ECU and the Pin on the Internal IC / Prosessor 120 KOhm with a DMM ,Yes you are correct the distributor runs at 1/2 engine speed that is 12 pulses in an engine cycle (720°) effectively 6 bangs per ref
I am curious why is the input impedance so important ?
hevans1944
Hop - AC8NS
@WHONOES would like to know the ECU input impedance to make sure his pulse circuit can drive it.
I don't know diddly about automotive ECUs either... the last car I actually worked on was my 1968 Mercury Cougar XR7, and it barely had controlled exhaust emissions that met 1967 standards. It did not have an ECU, but it did have a distributor for the eight spark-plugs and a set of cam-operated contact points, bypassed to the chassis with a capacitor (condenser for old-school mechanics) to prevent excessive arcing of the points by providing a conductive path for the back electro-motive force (emf) generated by the collapsing magnetic field in the primary winding, created when the points opened.
This capacitor was quite important for point contact protection as well as for controlling how fast the magnetic field collapsed. The voltage developed in the secondary of an ignition coil has almost no relationship to the turns ratio between primary and secondary windings because an ignition coil does not behave like a transformer with sinusoidal excitation. For a given primary inductance, L, the back emf when the points open is -(L)(di/dt), where di/dt is the time rate of change of the primary current, i, in units of amperes per second. This time rate of change of primary current is also proportional to the time rate of change of the decreasing magnetic field enclosed by the secondary winding, whose inductance can be quite large compared to the primary winding inductance. The result is a very large voltage developed in the secondary winding and a subsequent arc or spark at the spark-plug. A working arc gap (spark-plug) is absolutely essential to ignition coil performance. Without it, there is little or nothing limiting insulation breakdown in the coil and/or the ignition high-tension wiring.
If the spark-plug is causing electrical interference problems, there are several remedies you can try. The first (and most obvious) is to drill and tap a hole in either an aluminum or steel piece of stock for the spark-plug to screw into. Cover the protruding end of the plug with a hollow metal cap. Or drill and tap a blind hole for the spark-plug if a sufficiently thick piece of stock is available. Connect your ground lead for the coil to this metal block with a machine screw and a ring-terminal wire connector.
If available, it is advisable to use spark-plugs with built-in resistors, commonly used to suppress ignition interference with car radios. And finally, connect between the ignition coil and the now-shielded spark-plug using as short a length of resistive ignition wire as possible.
As you know, there are two adjustments on this type of distributor/contact points arrangement: dwell (how long the contacts are closed to provide energizing current to the ignition coil primary) and ignition advance (how many degrees before top-dead-center (TDC) that the contact points open, thereby collapsing the magnetic field in the ignition coil primary and creating a high-tension spark in the secondary winding that fires the spark plug selected by the rotating distributor arm. The purpose of a modern electronic ignition system is to replace the points that control the primary current, and to replace the mechanical arrangement that determines dwell and ignition advance. The distributor itself is now sometimes replaced with a coil-per-cylinder ignition, leaving only a "distributor cam" protruding from the engine block and equipped with Hall-effect sensors for timing information.
Back in the late 1970s and throughout the 1980s, automotive hobbyists (hot-rodders) here in the USA were experimenting with capacitor-discharge ignition systems that used an SCR to discharge a capacitor, charged to a comparatively high voltage, into the primary of standard ignition coils. Although this worked, after a fashion, there were some limitations to that approach. First, there was no way to allow a magnetic flux to (relatively) slowly build up in the primary and then suddenly collapse. The current build-up occurred rather quickly by "brute force" and then slowly collapsed as the capacitor ran out of charge. This was exactly the opposite of what happened with a conventional ignition system, yet because it was a brute force approach, the spark occurring when the SCR first discharged the capacitor into the coil primary, it was a significant improvement. Hundreds, if not thousands, of SCR-triggered capacitor-discharge ignition systems were built.
It took a perfect storm of legislation demanding better emission controls, and the development of power MOSFET technology to create modern ignition systems, now employed in virtually every new automobile manufactured today. You can take some advantage of this to test ECUs and ignition coils with the right circuitry.
I would wait for @WHONOES to finish developing his pulse circuit before returning to your 555 approach, but I believe you were on the right track and could eventually get your circuit to work.
The 555 circuit needs an external oscillator to make its output frequency variable, to represent revolutions per minute. This needs to be done because you want to control the pulse-width applied to the MOSFET switch to control the average current through the switch. To do this, the 555 needs to be configured in the monostable mode, so that a single pulse is output each time the external oscillator triggers it. You will have to control of the length of this pulse, which will be used to turn on the MOSFET and build up current in the primary of the ignition coil, to obtain the desired primary current. Your oscilloscope, in conjunction with a low-resistance current-sensiing resistor or (better) a clip-on current probe, will allow you to measure the primary current pulse. The resistor should be installed between the bottom end of the ignition coil primary and the drain of the MOSFET. The 'scope must be "floated" to measure the voltage across this resistor because the drain of the MOSFET is "above ground" until it is turned on by the 555. If you have a clip-on current probe, attach it over the wire that is connected between the bottom end of the primary of the ignition coil and the drain of the MOSFET.
Note that 555 timers are also available in two-per-package. Your external oscillator can be constructed from one half of a dual-555 timer operating in asynchronous (free-running, astable) mode. No need for a fancy wave shape, duty cycle, or pulse-width because its only function is to trigger the other half of the dual-555, configured as a monostable.
When the pulse applied to the gate of the MOSFET ends, current through the MOSFET abruptly ends and a back emf will be developed at the bottom end of the primary, across the now cut-off (non-conducting) MOSFET. This back emf is what you want to feed to the ECU speed input in series with the 6.8kΩ resistor, R1, shown on your post #41. It may need some further signal conditioning (attenuation, perhaps some low-pass filtering) to avoid either "burning out" the input of the ECU or confusing it with high-frequency noise. Perhaps your oscilloscope front-end needs protection, too. The best way to protect your scope is to use a 10X attenuated probe and the least sensitive vertical deflection. Increase the sensitivity until you have a recognizable trace that reliably triggers the oscilloscope horizontal sweep.
Probably the best way to find out if the ECU is working is to use an original coil (that you know is in operating condition) so that you can measure, with your oscilloscope, the magnitude and polarity of the pulse occurring on the trailing edge of the positive gate pulse applied to the MOSFET switch in your original circuit. You don't need the "snubber" circuit to protect the MOSFET, the two diodes and its internal body diode will do that. All a snubber will do is slow things down. My guess is this back-emf pulse may have to be attenuated before it is applied to the input of the ECU, but you will have to determine by trial-and-error (but not too much error!) what amplitude pulse is adequate but non-damaging.
Your schematic in post #41 indicates a back-emf of 200 to 220 volts, dropping to 110 volts at the "Engine Speed Input" of the ECU after passing through the 6.8kΩ resistor, R1. Since the voltage pulse dropped to (roughly) half its original value, you could assume the ECU input impedance is on the same order of magnitude as R1, or about 6.8kΩ. There may be other factors at play here, such as clamping diodes on the ECU inputs, typically used for voltage spike protection, and internal zener diodes that protect the front-end circuits of the ECU from excessive input signal voltages.
There will be a lot of "ringing" of the back-emf pulse if you look at the bottom of the ignition coil primary. This is because, with the MOSFET suddenly non-conducting, there are a limited number of ways to dissipate, or dampen, the oscillations that occur as a result of energy, stored in the magnetic field of the primary, oscillating back and forth between the inductance of the primary and stray capacitance in parallel with the primary. What an RC snubber does is dissipate the energy associated with those oscillations, but I don't think you need or want a snubber for this application. From the wave forms you have captured and displayed for us so far, it appears that the primary current oscillations are well-damped, probably from energy dissipated in the spark-plug arc. The negative swing of the oscillations is not good for the MOSFET, but it's body diode will "short circuit" those. The 1N5000 has a far too small inverse voltage rating, only 50 volts, to be of much protection against negative voltage being applied to the MOSFET. A fast diode with a higher voltage rating would be much better, or eliminate it entirely and rely on the MOSFET body diode to clamp negative drain to source voltages.
I am not familiar with Jaguar fuel-injected engines, or any other Jaguar engine for that matter, but I am not surprised that the Lucas ECUs are no longer available. So you just need to test what you have before committing to the purchase and restoration of a vehicle. To that end, I think your original circuit would be okay, if you could control the "on time" of the MOSFET switch to limit the average current to, say seven amperes. However, controlling the oscillation rate of the 555 timer does two things: it varies the "rpm" that the ECU "sees" at the bottom of the primary of the ignition coil, and it also varies the voltage developed in the secondary. This variation in voltage is something that is probably undesirable, and @WHONOES circuit prevents this from occurring because it separates the voltage generation function from the pulse switching function.
Looking forward to seeing more progress on your project. You should perhaps talk to Jay Leno about restoring old cars. He has a bunch of them (and motorcycles too!)
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Good Morning
Thank you so much for the very nice and valuable comments and the effort you putin to do it,I appreciate all Thank you so much,
This is what Thought but was not sure with my limited Electrical knowledge
To change the frequency I have to manually replace the Capacitor in the purple marking,
Current Probe wave form.
the wave from below is measured and compiled from a few cars just to verify that we have the right values in our heads
100 - 110V at the ECU input and interesting is with the right suppressor values at the Spark plugs (10KOhm standard factory suppressor spark plug leads) the negative spikes is not present on the signal as can be seen on my scope prints from the test setup so all your input regarding the interference solutions is 100% valid .
Thank you I will post my progress and errors as I go along,I am excited to get both circuit working the 555 and with the Help of WONOES his circuit as I learn many new things
Best Regards
from Russia
PS I saw you are from the US ,I worked at Polaris (snowmobile section) for 15 year ,was many times in Roseau,cold as Yakuts in winter and Wyoming , Minnesota
Thank you so much for the very nice and valuable comments and the effort you putin to do it,I appreciate all Thank you so much,
This is what Thought but was not sure with my limited Electrical knowledge
This is the problem with the current 555 circuit the frequency is fixed and the Gate Pulse Duty cycle can be adjusted which controls the Primary current ,This was my first problem and duke37 pointed that out ,I adjusted the Duty cycle and now the Primary current runs at spec,However at a fix frequency with the interference problem which you pointed at some good solutions
To change the frequency I have to manually replace the Capacitor in the purple marking,
Current Probe wave form.
my guess is this is part of the job of the 6,8K external resistor which is in series with the ECU pin,
the wave from below is measured and compiled from a few cars just to verify that we have the right values in our heads
100 - 110V at the ECU input and interesting is with the right suppressor values at the Spark plugs (10KOhm standard factory suppressor spark plug leads) the negative spikes is not present on the signal as can be seen on my scope prints from the test setup so all your input regarding the interference solutions is 100% valid .
This is very true I once many years ago was lucky when Lucas discontinued the ECU's I managed to get some drawings but not complete and in my situation the Engine speed signal circuit looks similar to this (there is just not good info on Automotive ECU's it is trail and error stuff)
Thank you I will post my progress and errors as I go along,I am excited to get both circuit working the 555 and with the Help of WONOES his circuit as I learn many new things
Best Regards
from Russia
PS I saw you are from the US ,I worked at Polaris (snowmobile section) for 15 year ,was many times in Roseau,cold as Yakuts in winter and Wyoming , Minnesota
Attachments
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See attached Pulse generation circuits. They are in two parts. The first part gives the pulse rate (period) whilst the second controls the pulse width.
The two circuits achieve the same result in slightly different ways. The first "IGN Pulse Gen" uses up most of the spare 40106 gates left over from the 200 volt generator. The second circuit "IGN Pulse Gen 2" uses just 3 of the spare 40106 gates plus a 555 to produce the actual pulse.
The notes on the schematics show Pulse rate and period. Accompanying graphs show results.
The pulse widths are about 230 to 250μS.
You could indeed use a dual 555 which is a 556 to generate the required pulses. It's just that the suggested circuits use up some of the spare 40106 gates.
The two circuits achieve the same result in slightly different ways. The first "IGN Pulse Gen" uses up most of the spare 40106 gates left over from the 200 volt generator. The second circuit "IGN Pulse Gen 2" uses just 3 of the spare 40106 gates plus a 555 to produce the actual pulse.
The notes on the schematics show Pulse rate and period. Accompanying graphs show results.
The pulse widths are about 230 to 250μS.
You could indeed use a dual 555 which is a 556 to generate the required pulses. It's just that the suggested circuits use up some of the spare 40106 gates.
I'm drip feeding you the various parts. The part that provides the 200V pulses is the final bit.
I am trying to get you to build a bit at a time and get it working. If you, or anyone for that matter, builds a whole project in one hit and then finds that it does not work, you will not know where to start fault finding. Whereas building it one block at a time then adding them together when you have them working gives you a much better idea of where, if it does not work, something may have gone wrong giving you a far better chance of fixing it.
I will post the last bit later but would advise you to build and test the pulse circuit first.
I am trying to get you to build a bit at a time and get it working. If you, or anyone for that matter, builds a whole project in one hit and then finds that it does not work, you will not know where to start fault finding. Whereas building it one block at a time then adding them together when you have them working gives you a much better idea of where, if it does not work, something may have gone wrong giving you a far better chance of fixing it.
I will post the last bit later but would advise you to build and test the pulse circuit first.
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Thank you so much this make 150% sense .
Have nice day I will progress in the next few days and come back when it is running or I made some smoke
Regards
I must mention that in the last schematic I provided, Q1 is labelled as a QMJE350. The Q prefix is an oddity of the simulator that I use. If you intend to buy the transistors indicated, just shop for an MJE350 and MJE340. Incidentally they are rated at 350V and have quite good gain for high voltage transistors.
Dear WHONOES,
I have now build the 200V Generator and the Pulse Generator circuits,at the moment I use breadboard until I have it all working then I will make a nice PCB ,the right bottom corner is reserved for the output stage,
The circuit runs as per your document with slight variation in pulse width and that is only because I do not have a 27nF capacitor for C3 ,I have only a 33nF ,
Scope print from the build circuit
I could not get the MJE transistors but placed an order ,once I have everything working I want to ask a few questions to help me understand a few things in the circuits.
However I appreciate your help things are going forward in great way.
I have now build the 200V Generator and the Pulse Generator circuits,at the moment I use breadboard until I have it all working then I will make a nice PCB ,the right bottom corner is reserved for the output stage,
The circuit runs as per your document with slight variation in pulse width and that is only because I do not have a 27nF capacitor for C3 ,I have only a 33nF ,
Scope print from the build circuit
I could not get the MJE transistors but placed an order ,once I have everything working I want to ask a few questions to help me understand a few things in the circuits.
However I appreciate your help things are going forward in great way.
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