speedometer speed sensor

Hello
at the beginning sorry for my english

I need to get the signal from this speedometer sensor
how can I read signal ??
the middle pin of the sensor leads to the on-board computer pin nr 21
I measured the voltage on pin 21 and shows a constant voltage of 4.5V
invariably the speed


Opel Calibra 92 2.0L 150HP
engine C20XE

You are going to need to either find the specifications for that sensor or look closer at the sensor output pin - it is probably a pulse, but you will need to look at it with a scope to see just what it is doing. You asked about a speedometer speed sensor, but that looks like it is on the engine - the "speed" you measure will depend on what gear you are in. I would expect it to be a magnetic pickup of some sort - probably a hall effect type sensor. The computer looks at the number of pulses/minute (or time between pulses) to calculate rotational speed.

this is a speed sensor I'm sure
It is the same speedometer cable
3 photo shows cable slot

(I mean the cable like this)

That is the this sensor without cover


It appears to be an automotive speedometer. The module fits in the slot that is circled in red in the third picture. My guess is a reflective sensor that counts the dark and light squares that you can see in the same photo.
Need a little clearer picture to be sure.

I found on the forum for more information
It is a photodiode

in the circle are 8 black and 8 silver (mirror) fields

how to read signals from the photodiode ??


really no one can help :frowning:

I would expect that the pin that goes to the computer has a pulse on it - you indicate it reads 4.5v all the time, however, I think that is probably what you are getting from a meter - you need to actually look at the signal with an oscilloscope to determine exactly what it looks like. The other option is to spend the time to create a schematic from the one you have. Assuming it is using the reflective blades as another suggested (which is probably right), there should be a combination LED and phototransistor etc. that shines on the blades and looks at the reflection. That would most likely (without seeing the schematic) give a square wave output from the photo-transistor. Exactly what is done with that before it leaves on the pin to the computer is what needs to be determined (hence the schematic). If it is a square wave (or pulse depending on just what goes on in the circuit), you count pulses for a known period of time (or time between pulses for very low speeds) to find your speed.

Thank you very much for help :slight_smile: