Hi everyone!

So at work we have several engine simulators and for the ones we currently have engine speed sensors connected to we went about it by using a DC motor spinning a magnetic pulser disc (found here) with the sensor mounted directly in front. Though this works fine, I'd like to start building improved versions of these engine simulators from scratch due to the ones we have being a complete Frankenstein mess over the years. Instead of using moving parts I'd prefer to be able to control the engine speed signals more digitally.

Last week I purchased one of these from Amazon in high hopes that it would generate the signal I was looking for since engine control modules interpret "digital" signals. However, when playing around with the little PWM generator a bit I couldn't seem to get any engine RPMs to generate. While in data monitoring mode, the only thing that I could see change was the "Engine Speed State" parameter. The 3 values available were "High", "Low", or "Triggered." With the PWM frequency below ~30 Hz the values would bounce back and forth between High and Low. Once I surpassed ~30 Hz then it remained on "Triggered" with any frequency higher than that. The actual engine speed RPM never really registered but occasionally you could see a number value pop in there for a split second.

Note: I believe the sensor we have hooked up to it right now is a hall effect style sensor. I'm not sure how to determine what the original sensor type would be off of the original vehicle but I assume it's most likely a hall effect.

Here are my questions/concerns:

1. Is a PWM signal the correct one to generate or do I need a sine or other waveform that the engine control module would need as input in order to output to a square wave on its own?

2. Is there an easier method to simulate this?

Any help is appreciated. Thanks in advance!

PWM or Pulse WIDTH Modulation is used to provide a certain voltage (after high freq filtered out). I think you want a variable (low) frequency generator. Hall effect signals are low V low current however some Hall effect chips include a voltage comparator giving a 0-5V digital signal. 600RPM is 10 cycles per second. A hall effect device requires power, coil (reluctance) pickup is just 2 wires. If you had an oscilloscope you could see the signal coming from the sensor.

 

I understand that but if it is edge triggered the width won't change just the frequency, correct?

The time of the detected object or tooth etc gets shorter with any increase in rate of motion or RPM Therefore the width of the pulse will be proportionatly narrower as speed of detected object increases.
Max.

 

I understand that but if it is edge triggered the width won't change just the frequency, correct?

I think what you're thinking of is the duty cycle. That will remain fixed, but max is correct in saying that both frequency and pulse width will change (although it's an odd way to phrase and present the info - I stumbled over it on my first read too.)

 

I think what you're thinking of is the duty cycle.

You hit it right on my head. I was thinking in terms of "mark space" and the ratio of that. Which posably could be the solution for the TS, a mark space generator circuit. Just one of many by a guy that recently passed on - http://chemelec.com/Projects/Hydrogen-1/Mark-Space/Mark-Space.htm

The mark space generator was something I was considering at one time for my EDM project, that's how I found it.

 

You hit it right on my head. I was thinking in terms of "mark space" and the ratio of that. Which posably could be the solution for the TS, a mark space generator circuit. Just one of many by a guy that recently passed on - http://chemelec.com/Projects/Hydrogen-1/Mark-Space/Mark-Space.htm

The mark space generator was something I was considering at one time for my EDM project, that's how I found it.

That's a very interesting circuit, Shortbus. Thanks for posting. I once built a similar circuit using a single MCU whose purpose was combining pwm with phase control on 110VAC so that a very short section (1 inch) of nichrome wire could be made red hot, without the cumbersome need of a step down transformer.

 

Also on a slightly allied note, I recently found a Romanian seller on ebay that sold laser cut acrylic discs I got him to cut some acrylic discs with window for slot-opto detectors.
Max.

 

Would something thile this help??

https://www.diyautotune.com/product/jimstim-v1-5-megasquirt-stimulator-w-wheel-unassembled/

or in the UK

http://www.megasquirtuk.co.uk/msstims.html

John ;-)