Hi
I want to check a button state which connected to a black box. Button may pull-up or pull-down, I can not consume any current from the system or cut the button wires but can T-Splice and use same GND. I can not decide that how can I achive this job properly, will I use op amp comparators or optocouplers... Any idea?
Thank you.

 

It would help if you told us what you wanted to accomplish with checking the button state?

 

It would help if you told us what you wanted to accomplish with checking the button state?

The buttons settled on steering wheel, and probably their outputs goes to can bus node. I would remote a car radio with different resistors which connected to same 5V supply.

 

Interfacing with the existing buttons is possible. Interfacing with a CAN bus is beyond me. I asked to clarify for those who follow me.

 

Interfacing with the existing buttons is possible. Interfacing with a CAN bus is beyond me. I asked to clarify for those who follow me.

I dont want to interact with can bus, just use the buttons for other purpose. After check the 6 buttons state I would decide to trigger 5V along relevant resistor node.

 

Ok. I reread your post and saw that you weren't interfacing with the CAN bus. The existing buttons did. Right?

 

If you take a photo and talk some more, it might be help to solve your problem.
If you can interfacing the button state out of the box then maybe you could just use a bjt as inverter to check the state of button.

If the button pull high then the bjt will goes low and can be turn on a led to indicates the state of button is at a high state, vice versa.

 

1. Do you and to say detect the state of the OEM buttons and EFFECTIVELY push say Vol up/Vol DN or Channel UP/channel DN on a new radio with physical buttons?

There was a thread on ETO that dealt with button detection. It may have used a DOT bar driver.

The steering wheel buttons on one of my vehicles include vol Up/Vol Dn and seek up and seek down and some other stuff.
Generally these buttons are not a matrix, but give you a different resistance when pressed. that resistance can be used in a voltage divider, to get a different voltage based on what is pressed.

The DOT/Bar driver chip is a pretty good way to linearly divide a voltage and get an output per range. e.g. 0-1 V, 1-2, V. 2-3 V etc.
To interface with the new radio, you can use an OPTO FET. Linear technologies TIMERBLOX might be low parts count. A micro such as a PICAXE with an A/D and however many outputs you need. To expand the digital ouputs, you can use an I2C expander.
I've used the OPTO- FETS before. You just have to check the on resistance for compatability. OptoMOS relays are also small.

 

Hi
I want to check a button state which connected to a black box. Button may pull-up or pull-down, I can not consume any current from the system or cut the button wires but can T-Splice and use same GND. I can not decide that how can I achive this job properly, will I use op amp comparators or optocouplers... Any idea?
Thank you.

If you can't draw ANY current from the system you can't connect anything to sense the switches at all.
Consult the tech manual for the car and see what the circuit is like.

 

My car's onboard radio was communicating with steering wheel buttons on can bus. Last year I change my radio with a new one but I lose steering wheel control buttons, because of new radio incompatible with can bus, it has only one wired remote input. My aim is install a line between the steering wheel buttons and new radio w/r input. So I want to combine two circuit: one is here (http://jvde.net/node/7) which consists kind of voltage dividers and the other one is button status controller.