LCD Instrumentation for Cougar Controller

[jackbauer]

Basically I identified the tach output from the ecu in the wiring harness. Then i used a 1k resistor and a random small signal npn transistor and drove its base with a function generator. I connected one end of the 1k to +12v , other to the collector , emitter to gnd and base to the sign gen via another resistor. I the connected the tach wie to the collector so it would swing from +12v to gnd. I might add that I obtained this information thanks to having the autodata cd on my computer.

As my car was a 4 cylinder it made sense for the tach to be a 2 pulse per rev of the crank and indeed this proved to be the case. Once i had this info i purchased a cheap npn industrial proximity sensor on ebay. I drilled the com end on the motor with a 50mm hole saw so as to expose the com end bearing. I epoxyed two little "buttons" made from some 6mm steel bar stock to the inner race of the bearing. Mounted the prox sensor on a little bracket so that the buttons swung past its face. Connected up a 1k resistor on the collector of the prox sensor output transistor as before and that was that.

This system has worked perfectly and feeds the dash tach and the controller rpm input (via a 4v7 zener). I do laugh sometimes when I see these rpm pickup systems for sale from some ev suppliers. Don't think my setup cost 10usd!

If anyone wants me to lookup a specific vehicle on autodata and provide pin data and signal levels for the tach i can do so.

Finally apologies to Freyguy for going off topic

edit: found a pic.

[harlequin2]

Hey Chris, that's pretty simple, I will have a look at it. And Jackbauer's tacho drive is very elegant! The reason I figure I don't need a tacho is that my car is direct drive, no clutch and it is not possible to rev the motor past about 3500 rpm ie top speed of 110 kph - might get a few more revs if I wire the motors in parallel instead of series, but that is quite adequate as it is.
I'll keep the fuel gauge drive as that is very nice and probably use the alarm output for the tacho/ammeter.

[Freyguy]

Originally Posted by jackbauer

........Finally apologies to Freyguy for going off topic

edit: found a pic.

If it has to do with EV instrumentation it's "on topic" as far as I'm concerned. Besides, we've all seen your work. When you have something to contribute it's always worth the space

[ianbartie]

I have a Cherry proximity sensor already fitted with 2 sensing magnets. Was originally going to be an rpm input for the Cougar but the firmware still does not support it (AU version).
I hooked it up to 12V with a 2.4K pullup resistor & tested the output. Got 12V pulses OK but the tacho does not respond.
The output on the scope showed the square wave from the sensor is about 90% on & 10% off.
The original square wave driving the tacho was 50% on & 50% off. I scoped it before I pulled the motor out.

I can follow circuit diagrams & make something but I don't know how to go from the signal I have got to the signal that I need.
Driving the tacho seems to be a bit of a problem for many EVs.

[jackbauer]

Your problem could be that your using a magnetic sensor so its holding on due to the magnetic fields. If you use a normal hall type that just detects metal within 3mm like mine it should be ok. You can then vary the mark to space ratio with the size of the metal pieces.

[Freyguy]

Originally Posted by ianbartie

I have a Cherry proximity sensor already fitted with 2 sensing magnets. Was originally going to be an rpm input for the Cougar but the firmware still does not support it (AU version).
I hooked it up to 12V with a 2.4K pullup resistor & tested the output. Got 12V pulses OK but the tacho does not respond.
The output on the scope showed the square wave from the sensor is about 90% on & 10% off.
The original square wave driving the tacho was 50% on & 50% off. I scoped it before I pulled the motor out.

I can follow circuit diagrams & make something but I don't know how to go from the signal I have got to the signal that I need.
Driving the tacho seems to be a bit of a problem for many EVs.

Ian,
I am using a cherry proximity sensor as well, with two 5mm diameter rare earth magnets embedded 180 out on an aluminum collar on the back of my motor shaft. They recommend a 2.4K pullup, but I used a 1K since its rated to 25mA. Being rare earth magnets the fields are strong, but my duty cycle is nowhere near 90/10. I'll have a look on the o-scope tonight and let you know what it is.

[Freyguy]

Ian,
My duty cycle measures 80% high/20% low. A low corresponds to a magnet positioned in front of the sensor. From a surface area standpoint, the 5mm magnets represent 8% of the collar’s circumference so the additional 12% must be due to field strength tripping the switch’s thresholds on approach.
I’ve attached a picture of my setup. The collar is plastic with a single set screw (aligned with shaft keyway) purchased from McMaster Carr.
My apologies on the sensor. Mine is made by Hamlin, model 55140-3H-02-A although Cherry does make a similar model MP102101.

A function generator with adjustable duty cycle would be a helpful tool but odds are you don’t have one. As a test you could attach more magnets around the circumference so that the space/mark ratio improves to the point the tach responds. With that “minimum” ratio known, you could then find larger diameter magnets that can satisfies this criteria with only 2.

[ianbartie]

I put the scope on my Cherry 101301 sensor (& put my glasses on too). It is pretty close to your results. I have the original camshaft position sensor which is an inductive type so I made up a sensor wheel with 4 equal mark/space segments. That should give me the right length pulses, which it did but it was not a proper square wave & the tacho stayed still.
The original pulses from the ECU were a perfect 12V square wave 50% on & 50% off which only varied in frequency. The tacho in these newer VWs are a stepper motor type so I am guessing it was a PWM signal the ECU was outputting to drive the tacho.
I am thinking along the lines of some sort of 555 circuit that outputs the correct 50% duty cycle square wave with the frequency being altered by the Cherry sensor input.
Simple, huh - except I have no idea how to do it.

[Freyguy]

Originally Posted by ianbartie

.....The original pulses from the ECU were a perfect 12V square wave 50% on & 50% off which only varied in frequency. The tacho in these newer VWs are a stepper motor type so I am guessing it was a PWM signal the ECU was outputting to drive the tacho.

If your sure it was a constant 50% duty that only varied in frequency then it can't be PWM to drive tacho. Lets just approach it then as varying frequency with fixed duty.

I am thinking along the lines of some sort of 555 circuit that outputs the correct 50% duty cycle square wave with the frequency being altered by the Cherry sensor input.
Simple, huh - except I have no idea how to do it.

I'd use the sensor wheel you made up with 4 equal spaces per revolution. Feed cherry output into the attached circuit (input pullup required as well as decoupling cap on pin 14). It is a divide by two flip-flop made from a CMOS 4013 (dual, but we use one). Output will be 2 pulses per rev at 50% duty regardless of frequency.

[ianbartie]

Thanks Freyguy,
I am 100% positive that it was a constant 50% duty cycle with only the frequency changing as I revved up the motor.
I made up a simple 200Hz square wave generator that has a 50% duty cycle to test the tacho. I'll try it this morning & get a CMOS chip when I go to town later today.