Looking for help! Hall sensor to relay

Thread Starter

Sleven

Joined Oct 18, 2023
5
I am hoping someone can help me on a project I am working on. I have converted a car from automatic to manual transmission. Mechanically everything works great but I am having an issue with some of the electrical.

On the clutch pedal is a hall sensor with 4 wires. 12V power, ground, and two output wires. The hall sensor came with the clutch pedal/master cylinder.

On a bench from a 12v battery and with my multimeter,I have the follwing;

Pin 2 has 0.002v when the clutch pedal is not pressed and 0.00v when the clutch pedal is pressed
Pin 4 has12.78v when the clutch pedal is not pressed and 10.49v when the clutch pedal is pressed.

I would like to use the hall sensor to control a relay that will close a circuit on the neutral safety switch when the clutch pedal is pressed allowing the car to start. Currently I have bypassed the neutral safety with a jumper so the car will start in gear without the clutch pedal pressed, but this is a big safety issue and this was done for testing purposes only.

I’m really not sure how to go about controlling a relay with a hall sensor like this or if it's even possible. I apoligise for any dumb questions in advance as I am very inexperienced on this sort of thing. Hence why I am here. Any help would be appreciated. Thank you!:)


CM pinout.png


Any help would be appreciated.
 

geekoftheweek

Joined Oct 6, 2013
1,169
What kind of vehicle is this? Some vehicles use a PWM signal from their sensors which is a square wave of a certain frequency that changes the relationship of the one time to off time to indicate whatever it is they are sensing. It will show up as a variable voltage when measured with a meter because the meter is showing an average instead of constantly changing between a high voltage and low voltage as would happen with a PWM signal.

The only real way to tell for sure is to connect it to a scope and inspect the waveform.
 

Thread Starter

Sleven

Joined Oct 18, 2023
5
Thank you for the reply.

It's a 2008 Lamborghini Gallardo, but the same hall sensor is used on quite a few other cars from VW and Audi. It's one they use on most of their cars. I'm really not sure if it's a PWM signal or not. I will try to find out.
 

geekoftheweek

Joined Oct 6, 2013
1,169
The reason I asked is this sounded extremely similar to another post several months back involving a Ford van. They are good for using PWM signals on sensors.

I may be wrong, but the voltages you mentioned seem strange. That is what lead me to the PWM thought. I've never worked on a Lamborghini though so it's possible it may be totally normal. I'm skeptical I'll find any useful information online that describes how it is supposed to work, but I'll look around a bit tomorrow in my free time.
 

geekoftheweek

Joined Oct 6, 2013
1,169
@Sleven I did some digging around with various search phrases related to VW, Audi, and the part number and couldn't find anything that described what kind of signals to detect.

I am assuming you have a new switch and the readings are at least what one would expect although the relatively small change on the cruise signal makes me think there is something missing that would take someone actually familiar with how it is supposed to work to know. I kind of wonder if that particular pin in an open drain for some reason. If you aren't using it for anything then it doesn't matter.

If it is a constant voltage signal you could easily use a comparator and a few other components to drive a relay. If it's a PWM signal or some other coded signal it's going to take a lot more effort to make it work.

I wish I had a better answer
 

Thread Starter

Sleven

Joined Oct 18, 2023
5
Thank you for looking into this. Upon further testing I hooked the 12V singal wire to a relay and the relay closed when the clutch is not pressed as the output from the hall sensor was around 12.7V. So, I think this would work, however I need the relay to activate when the pedal is pushed at the lower voltage. So, the system is basically reversed right now. I tried switching the inputs on the hall sensor, but no luck. Any suggestion how I can wire this to make it work? maybe with a couple of relays

Thanks again
 

Thread Starter

Sleven

Joined Oct 18, 2023
5
just to add, the hall sensor is acting like a switch and normally closed in the resting position. The curcuit opens when the pedal is pressed. I need this to be open in the resting position and closed when pressed. I don't think I can change the way the hall sensor works but there must be a way to close a circuit when the clutch is pressed.
 
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