A short preface... I've searched the forum and have been unable to find the particular answer to my questions. I'll ask following this introduction as I need to clarify my intentions. I wish to use the drive by wire pedal in my car as the input control for a servo to control the cowl hood slot. I have an Uno with a Drok buck converter (5V) currently connected. I've been able to find the Vref 2-4VDC out from the pedal to the ECU. I would like to optically isolate this sigal as I do not want to invoke feedback or noise to the ECU. My thoughts were analogread to pin0 but without reference to the pedal i'm reading a small change after the DAC. With a meter I can see the full sweep (+/-2V) but on the serialprint it's only 480-510. I do not want to change anything on the car! I do not want to incure any change that could potentially cause harm to myself or others. I only want to read the signal and generate the PWM to control the servo. Unfortunately, the pedal does not have a pin that I could attach an external pot to otherwise I would have already gone that route. I do have another option but don't know how to achieve it. The Cruise control input (aftermarket) uses a 4k PPM square wave signal sent from the dakota digital dash cluster controller. And the final option is the tach signal also from the controller. Again I do not want to backfeed the controller or conflict with my ECU. I just want to control the servo to angle the cowl via the pedal/engine speed. This is strickly cosmetic as the intake is not connected to the cowl. Any assistance would be greatly appreciated. I used a hobby servo on the 5V buck converter and PWM is connected to A4 on the uno. The only code generated thus far was analogread on 0 and serial print so that I could map the pedal. I'm fairly new to code and am a novice at best but I do understand electronics. Thank you for your help kindly in advance.
Post a wiring diagram of your setup. Sound like a missing GND connection but that's wild guessing.
In the circuit description I cannot find the optical isolation you mentioned.
This sounds like a fun idea but do you understand the liability if you place this vehicle on the road? Thoughts: Is the UNO is rated for automotive, I do not think so. The electrical environment is not a simple 12V the vehicle is expected to survive and operate a short time from 6V to 18V some even to 24V. I have seen transients to over 400V. Good luck but because of the implied liability I am not helping on this.
Linear optical isolators exist but they require some input current (~10mA) similarly to a digital version and therefore would load the input to the ECU and perhaps cause problems. You could buffer the pedal pot output with an op amp but you would risk some sort of catastrophic failure mode.
Show us a drawing of the pedal arrangement and maybe we can figure out some way to add a sensor of some sort. The sensor doesn't have to be another potentiometer, just something proportional to throttle position.
Is there feedback from the throttle itself that could be piggybacked on. Some control systems have a feedback signal to tell the ECU that the amount of throttle asked for was provided.
Your reply was perfect. Thank you for the info on the optical isolator. I was hoping i could just read the output from the pedal using an isolator but I do not want to risk altering that signal. Internally it is just 2 pots with opposite feedback that the ECU reads for pedal position. I've had my head stuck on adding another pot but your statement "just something proportional to throttle position" struck me like a brick. Thank you! A slider pot from an old EQ or stereo would easily mount to the side and use the pedal arm to change position. I can then use the standard pot control to servo code and voilà. I was, as usual, trying to overcomplicate it. That's why a community forum is helpful. Different view points. Thanks again.
I'm glad my comment triggered an idea you can use. Like you say, sometimes a different perspective is all it takes. Enjoy your project!
Imagine that slider got entangled while driving and the pedal stays down...
A car is a lethal weapon and shouldn't be used as a playground.
If you use the built-in pods the worst you might trigger is a car not driving anymore but it won't be kept at 100km/h unintentionally.
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