Transistors - witchcraft? Home electronics help!

[timmymagic73]

I appreciate there are dedicated forums for this kind of thing, but I have a login here and I know someone on PH is bound to know the answer...

Vaguely car related, I'm creating a wired remote for a Pioneer AppRadio (DA120 to be precise) following the work that's already been done here:

http://jvde.net/node/7

Rather than using switches however, I'm trying to use a rotary encoder for volume up/down in conjunction with an Arduino board. I'm a programmer so the cut/paste of code is no problem , the encoder is responding as I expect - but it's the component side I'm struggling with.

This is the board I've built.


The grey wire is ground. Purple and Blue are Arduino controlled pin outs @ 5v. Tracks run vertically, the only bridge is the bare earth wire at the bottom.

With no power connected, if I measure resistance across grey and white I get exactly the results I expect when bridging the Collector and Emitter on each transistor.

When the Arduino supplies 5v to the Base to switch the transistor, it all seems to go wrong and I'm not sure what I'm measuring - the resistance of the Arduino board too?!

Does anyone have any thoughts? I'm debating using a 2 channel solid state relay instead to totally isolate the switching side from the Arduino.

Cheers!

PS: I realise TIP122s are massive overkill for this, but as I had them lying around...

[Stiggolas]

You can't measure resistance with the power connected, you will get weird results. Your multimeter works by putting a voltage on the probes and using ohms law to get the resistance. Any voltage already there will screw it up.

[timmymagic73]

Thanks for the replies, much appreciated. I have limited experience with these NPN transistors as I'm using them in another Arduino project just to switch a 12v 10w LED, but obviously I wrongly assumed that they could be used as switches in this way.

It seems the simplest solution might be a 2 channel Solid State Relay to convert the Arduino pin out 5v to a basic switch.

I'm simply trying to connect a set resistance value across the ground and tip of the Pioneer wired remote, so the relay seems like the dummies way of doing this without getting into digital potentiometers!

Cheers.

[StanHansen]

Oh yeah, I remember when I tried to do the same with my transistors. My dad had Pioneer AppRadio and asked me to fix it when it broke. I failed every time even with my electronics background (college level). I think there is a need to found a wiring scheme in order to understand all the details but unfortunately I couldn't find it on the internet. The wiring scheme really helped technicians who did a dryer repair for me several months ago. Though I think there should be several videos on youtube that can help to fix your AppRadio.

Edited by StanHansen on Wednesday 30th December 09:45

[Troubleatmill]

StanHansen said:

Oh yeah, I remember when I tried to do the same with my transistors. Failed every time even with my electronics background (college level).

You might be 2 1/2 years too late to assist.