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Finding the right switch

KilgoreCemetery

Apr 12, 2017
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I'm trying to add a bluetooth module to an AM/FM radio in the least destructive manner possible and I feel like I have one last obstacle to overcome. I want to replace the existing rotary switch with one that you can also push in to activate another function.

The original switch has a detent to signify an On/Off state, but also acts as the volume control as well. It's knurled and slotted. This switch controls the AM/FM side of things. What I'm wanting is to replace it with a switch that does all these things plus push in to turn on the blutooth side and turn off the AM/FM side.

What I'm wondering is if such a beast even exists and, if so, where would I find one? Am I trying to do too much with one little switch?
 

kellys_eye

Jun 25, 2010
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The only types I've come across have been used in oscilloscopes whereby the knob has a 'pull out' position as well as the conventional rotary-and-switch function. Not sure where you'd go to get one either as the carbon track values have to have a suitable resistance and a logarithmic function too.

Consider putting a small slide switch on a rear panel instead.
 

KilgoreCemetery

Apr 12, 2017
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It seems like if there is such a thing, it must be used in something out of the ordinary. I was thinking maybe a guitar pedal where you would rotate it to adjust the tone or something, but then step on it to turn it on and off. I'm not sure that that is how they actually work, though, and I live in a small town with no guitar shop where I could just go look at them.
 

KilgoreCemetery

Apr 12, 2017
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I guess the real question is how would they be categorized? Are they SPST Push/Push? SPDT? DPDT? I don't quite understand what the different designations mean in practice. I know the original switch is just a simple SPST though. I just need one that adds the push/push feature
 

kellys_eye

Jun 25, 2010
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The function of the switch depends on what you want to achieve and would be selected to meet your own needs/spec.

What you could do is fit an internal microswitch that is operated when the radio tuning dial is at one extreme or another. The tuning capacitor usually has a larger plastic drive (dial) attached and fitting a microswitch against it and filing a small slot for it to operate the switch could be done.

Hot glue gun, small file, soldering iron. Job done!
 

Decky

May 17, 2017
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I've seen rotary controllers with a push switch function (like a domestic dimmer switch) but I've never seen it on a rotary switch. I don't know what your engineering skills are like but if that's the function you need I would try and rig up a latching push switch behind the rotary switch so that it switches every time you push the rotary switch in and release it (assuming there's room inside the radio). The rotary switch would always be supported by the spring tension of the push switch behind it (if it was big enough) but it will also need some kind of support structure around the sides of the rotary switch to stop it moving away from the axis of push and return and also keep the push switch in a fixed position. I couldn't comment on what that would look like without seeing the rotary switch. You would be able to choose the latching push switch so that it performs the exact type of Bluetooth switching required (DPDT, etc.). An interesting challenge indeed!
 

kellys_eye

Jun 25, 2010
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The rotary controller you're referring to is an 'encoder' and will require a digital (processor) interface to resolve into the analogue replacement for the original volume control.

Whilst it's a potential solution to the OP's needs it may well be far more involved and complicated to implement considering the basic requirement of the original need.
 
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