Volume control with rotary encoder and pushbuttons?

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This is from a JVC but the function is likely the same. It appears that the volume is stepped when one transitions from high to low then the other transitions the same. They can begin at ground or at 5v. The up/down is determined by which one transitions first. The two images show volume adjusted one way and volume adjusted the other way. I don't remember which is which.
 

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You really do need to get a scope onto the encoder. I have bought 3 batches off eBay and now have three different types of encoder.

One is Gray code, one kind of binary one the third is quite silly but works. The micro I use these on now has three sets of code in the isr that handles this, and jumpers so I can tell it what to look for.

The message being: just shorting wires on an encoder input won't work. Pumping a square wave in might do something, but odds are it will not be useful.

You can definitely develop an emulator for it. Easiest way would be using a micro controller. That way you could mix in the second rotary encoder by reading that in the micro controller, combining the resultant commands and driving one set of outputs to the head unit.

Sounds like a lot if work to save moving your hand one foot from he steering wheel.
 
The circuit below works in the JVC head unit. The switch could be replaced by a 555 timer output set for 2-3Hz. The outputs have to be reversed to step up or down. This could be done by two double-pole relays with opposite connections. One would be engaged to step up. The other to step down.

If you do this, you will probably have to remove the encoder. The encoder can stop open or shorted. If it is on a shorted location, the circuit cannot drive the signals to the processor.

The circuit requires an op-amp that can accept inputs at ground. Many audio op-amps cannot do that. The circuit works with an LM358 and a TLC2272. The 2272 swings rail to rail so it provides a bit better pulse but either should work.
 

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Would this work for the volume control push buttons? I'm not 100% sure the diode next to the switch will allow the up button to ground pin 3 only and not the DPDT. Then the down button would ground pin 3 also and the coil for the DPDT relay to reverse the output.
 

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