So you don't need the pot for anything but the extra injector pulses?
I don't think it would be too hard. First off you set up the pot to give voltage as a function of position, then differentiate the voltage (with a capacitor and resistor) to get rate of voltage change. This can operate a multivibrator which supplies the required pulses, synchronized to crankshaft rotation if needed.
Tim
-- Deep Fryer: a very philosophical monk. Website:
A part called the "throttle switch " for the early Jaguar V12 is no longer available. Its main function is to generate extra pulses to the fuel injection system when the accelerator is quickly pressed. The switch is mechanical, attached to a rotating shaft attached to the throttle capstan. A path to ground as makes and breaks as a rotating contact arm slides along serrated copper anth on a small circuit board. So basically, it can be thought of a switch that opens and closes 10 or 12 times (I've forgotten which, but I can look it up) as the throttle moves from idle to full open.
Later models of the same engine have a different electronic control unit (ECU) which relies on a throttle potentiometer instead of a switch. For several reasons it is not practical to switch to the newere ECU, but the thought has occured to me that I might be able to use the newer throttle pot to replace my switch. Mechanically, it fits exactly in place of the switch. All that would be required is a circuit that takes the linearly varying resistance from the pot and generate outputs that simulate the 10 (or 12) closures of the mechanical switch.
I'm not prepared to launch this effort immediately, as I'm not sure current running problems are due to the throttle switch, but I would like to here some ideas on how to approach this.
TIA
Ed
Ok, then you can commit the pot to your circuit.
You could do that, or you could just gate the pulses, so more pulses come out when the dV/dt is higher- whatever you need.
Sure. Or you could use two transistors, or an op-amp, or a whole PIC...
Well, as I understand it, it's rather pointless to have the injectors squirting against closed valves.
Unless the computer does later processing on the pulse signal.
Tim
-- Deep Fryer: a very philosophical monk. Website:
-- So it sounds like you want something to generate 12 pulses as the accelerator goes from idle to full open. From your description of the switch it doesn\'t sound like the thing needs to be conscious of how quickly the accelerator is pressed, it just needs to output a pulse at each of the 12 switch points when the accelerator is moving away from idle, true? If that\'s true, then by far the easiest way to do it would be to use a microcontroller with an on-board ADC. Program a lookup table in the µC with the switchpoint voltages, wire your pot like a voltage divider and scale its output to be compatible with the µC ADC input, and keep track of whether the input voltage is increasing or decreasing and whether it\'s equal to the switchpoints in the LUT. Y pu can do both by monitoring the output of the ADC and comparing it with the magnitude of the previous switchpoint acquired. If the magnitude of the current switchpoint is greater than the magnitude of the previous switchpoint, output a pulse. If it isn\'t, then don\'t. It sounds that since ground is what\'s being made and broken and it\'s being done with a mechanical switch, you\'re doing low-side switching, so I\'d use a logic-level N-channel MOSFET with a low channel resistance to simulate the device that\'s doing it now.
Thanks, Tim.
Don't think so. I believe that the ECU needs only the pulses and indications of idle and and full throttle conditions.
So when the throttle is not moving the rate signal is zero and the multivibrator is not generating any pulses. Would the multivibrator pulse frequency be higher when the rate of voltage change was higher?
Could a 555 IC be used as the multivibrator? I'm somewhat an amature, but I have built some circuits using it.
I don't understand your remark about crankshaft synchronization. Not talking about ignition here.
Thanks again.
Ed
Tim,
Don't understand... what dos "gate the pulses" mean?
This is a very early FI system. Although there are 12 injectors they fire in groups of 6, 3 on one bank and 3 on the other. These are indeed synchronized with crank position, so that a few cylinders are getting pulse a bit early and a few a a bit late. Anyway all of that is handled in the ECU, driven off a trigger in the distributor. The pulses generated by the throttle switch are extras, just enriching the general mixture in the manifold at the moment you hit the pedal.
Thanks again.
Ed
Thanks, John.
That's correct. There should be more pulses per unit time if the throttled quickly, which happens naturally in the existing device.
The only state the current device is aware of is which direction it's going. A little backlash is built in between the throttle shaft and the wiper, and there's a double sided switch with some friction that tends to stay with the shaft. Which side of the switch is closed is indictive of the current direction. It is used to ignore the rotating switch during decelertion.
Sounds neat. I've never done anything with microcontrollers, but guess I could learn. I'm aware there is PC based software for programming them.
Thanks again.
Ed
Holy shit John, I *joked* about using a PIC, you can't possibly be a real professional and say this with a straight face!?
Tim
-- Deep Fryer: a very philosophical monk. Website:
run the signal from the pot into a DAC and adjust the circuit to give whatever number of transitions on one of the DAC outputs,
it might be simpler to use a disc with holes drilled in it and an optical sensor.
Bye. Jasen
--- Sure, why not? It's the best solution for the problem, which is to generate a single pulse at 12 different accelerator positions when the accelerator is moving _away_ from idle, but to generate none when it's moving back toward idle.
To do it in hardware and get the same functionality you'd have to do something like this:
V+ | [RT] VREF | +-------+ | V+ V+ +---|TH OUT|-->OUT [R1] | | | |_ | | [100K] [10K] +--O|D | V+ +----|+\\ | | | |_ _| | | | >--+--[0.1µF]--+------|--O|T R|O--V+ [POT]--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R3] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R4] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R5] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R6] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R7] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R8] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R9] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R10] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R11] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | | V+ | | [R12] | | | | [100K] | | +----|+\\ | | | | | >--+--[0.1µF]--+ +----|----|-/ | | [R13] | GND
Not bad, but with four chips, 27 resistors, and a cap, the single µC seems like a nice way to go. Of course, if you don't have the skills and the tools you'll _have_ to go hardware...
-- John Fields Professional Circuit Designer
-- How would you go about doing that, exactly?
say it's an 8 bit DAC, running off a 5V supply, stick a variable resistor, or resistors in series with the pot so that the pot only seex 75% of te DAC'c Vref range. because the pot doesn't cover the whole range of the DAC's input, for the full travel of the pot bit 0 will transition 192 times for 96 pulses but bit 3 will pulse 1/8 as often - 12 times
At the time I posted that I hadn't read of the unidirectional requirement,
it's take something like an edge triggered latch and a gate in addtiton to the DAC to do that...
Bye. Jasen
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