Hello all, I was after some advice. I would like to design a circuit which would allow for 2 inputs and 1 output in the form of headphones/ear piece. I would like for one input to get priority over the other. So if you arnt getting a signal from channel 1 you get it from channel 2. It needs to be a passive device if at all possible. Any ideas/starting points. I have been doing a fair bit of googling. Andy
Many if not most phono jacks have an unbuilt switch, so you can wire them up so that one overrides the other when plugged in. If you also need reduction from a high to headphone level, you can just use a pair of voltage dividers, which is a few resistors.
I think if you want to design a circuit and not know where to start, you probably should be reading up on basic electronics before you start. I dont really get the time these days, but if i do, i will see if i can knock something up, but this wont mean you are designing it.
So by passive you mean you don't want external power? Are the mic inputs 'pre-amped' at all? If so the lack of external power may be possible but you will most likely need external power. Get back to me and I'll get a design together for you.
What you can do is use one of these switched sockets for the master priority socket #1: http://www.maplin.co.uk/pcb-mounting-3.5mm-stereo-socket-1199?c=so&u=strat15 And one of these basic ones for the low priority socket, lets call it #2: http://www.maplin.co.uk/pcb-mounted-3.5mm-stereo-socket-1191?c=so&u=strat15 You can then wire the output of #2 socket to #1, and whenever #1 is plugged in, #2 is interrupted. The output of #1 can then be wired to another basic socket, just as used for #2 for the output. If the input is a high level signal, you will then need to use a pair of resistors to lower the voltage... as for what values, that depends on your signal and headphone type. This is a passive setup btw, no external power required. If you're just dealing with line/low power levels, then you won't need any resistors to drop the voltage, the signal will be ok for driving headphones, but Boscoe was suggesting, if you want to drive some powerfull headphones loudly, then you'd probably need a little amp, which means it would be active & require a power source. Now if you want a setup where both plugs #1 and #2 are connected, and the circuit can detect which sources have a signal, whilst giving priority to #1... well that's an active circuit that could end up being a little complex...
The system would need to know when input 1 was giving a signal. The overall device would take inputs from a VHF radio and from an ipod for example to an earpiece. Then when you get something transmitted over the VHF radio the ipod cuts out so you can listen to it. Thanks for all the help so far!!
ahhh, well you want the complex active circuit then! I think it could be done with a couple of op-amps and comparators, but i'd have to spend some time on the drawing board figuring that out There are a couple of other passive solutions that might interest you? One way would be to try connecting the two signals from the VHF radio and ipod together, so whenever something is picked up on VHF, you can hear it mixed with your ipod music. This system relies on you then turning the ipod down so you can hear the VHF radio clearly, and of course not having the ipod so loud that you can't hear the VHF in the first place. Another way is two have a manual switch, where in one position you can hear the ipod, and the VHF sound powers an led. Whenever the led lights, you can flick the switch to hear the VHF radio instead. Or just have the ipod go to one ear, and the vhf to the other ear
I would love to be able to do it all in one box. I will do some more research too, it would be nice to know more about this field.
