# Please explain this circuit to me

#### gregeeh

Joined Oct 19, 2021
19
Hi all,

The circuit below is for the steering wheel buttons on my car. I'm interested in the buttons between pins 1 and 6 and wondering what they might be connected to externally to the steering wheel. Yes they are just switching in various resistances but is there any reasoning behind the resistor values and why is RH (4.3K) so much larger then the rest.

You might ask, why the interest. Well, the vehicle does not remember that SWH (LFA) was pressed between engine restarts. Meaning each time I restart the vehicle I have to press this button. So I was going to install a relay and have it put 7.93K across pins 1 & 6 for a couple of secs when the engine is started.

TIA

#### ronsimpson

Joined Oct 7, 2019
2,404
Interesting RH=4.3k while R7=4.3 ohms. So R7 is mislabeled and should by 4.3k.

I have used this idea in sever products where there are (about) 6 switches and I only have 3 wires to read the switches. The computer reads the resistance (or the voltage divider) to find which switch is pushed.

I think pins 1 & 2 go to power (or a reference voltage). The computer looks at pin 7 & 8. So try your resistor from pin 6 and pin 7. I applied +5 volts to pin 1 and read back pin 7. But that is just how I did it.

#### gregeeh

Joined Oct 19, 2021
19
So try your resistor from pin 6 and pin 7.
I was going to put 7.93k between 1 & 6 to simulate pressing SWH (LFA). Do you think this is incorrect?

#### ronsimpson

Joined Oct 7, 2019
2,404
I think it is 7&6 but give both a try. Won't hurt if I am wrong.