Transformers Voice Changer Switch Help

[darthjag]

I am in dire need of help, I have gutted a voice changer from an Optimus Prime toy helmet that used a button on the side of the helmet to activate the microphone. The problem I have is once the button is pressed the Microphone only stays active for a few minutes and shuts off until the button is pushed again. Its a contact button on the board similar to those on a remote control, you will have forgive me as I dont know the name of this type of switch. I need to find a way to keep it on and keep it from timing out. There is an on/off switch for the power itself, is there any way to tie it into that or a way to turn whatever is timing it off ?

I hope that wasnt to confusing, any help would be appreciated !!

 

[Harald Kapp]

What happens if you use a switch instead of the momentary button? Does the mic stay open?
If not there is surely a timer within the circuit which needs to be located and bypassed. A good photo of the board (with legible IC inscription) will be helpful.

 

[darthjag]

Thank you so much for answering ,

I am pretty sure there is a timer circuit as I have tried keeping the circuit closed and the mic still only stays open for a shot period of time. Here are some shots of the board, the one I am
concerned about is P12, the other two just trigger some sound effects and I am not concerned about those but I am going to assume they run through the same timer .

 

[Osmium]

An alternative approach, especially if you can't figure out how to disable the timer on the board:

It seems that the circuit is "edge triggered" - it has to go through the cycle of the button being released and then pressed again to enable the circuit. You could possibly make a small circuit (based on a 555 timer, say) to act as an electronic switch which is continually cycled (pulsed). You want the switch to pulse fast enough that any delay caused by the circuit being off is not noticeable - 1Khz maybe? A possible downside might be that the pulse frequency could feed into the output circuit and distort the result - increasing the frequency to above 20Khz might solve that if it happens.

 

[Harald Kapp]

Sorry, there's no timer obvious to me on this PCB. It is probably part of one of the ICs under the black blobs. And it is edge triggered, as @Osmium writes, otherwise a constant on switch would have helped.

An automatic trigger based on a 555 seems a good idea. Although I'd set its frequency at the lower end, e.g. once a second because the mic is open for a few minues once triggered. This will work if the timer is re-triggerable (not every timer is). You'll have to test whether that works: When you keep pressing (and releasing) the button every few seconds, does the mic stay open for an extended period of time or does it still close after the initial delay?
If it stays open, the timer is re-triggerable and an automatic trigger as suggested by Osmium should work.
If the mic still closes after the initial delay, you'll have to live with a short interruption because the re-trigger can only work after the mic has closed. In this case a higher frequency in the kHz range will be better suited.

 

[darthjag]

Thank you both so very much for the advice !! Looks like its re-triggerable ,and looks like I am going the 555 route . I just have one more question, once I have put the 555 together should I be soldering the out pin to the edge trigger or where would I be connecting the output to ?

 

[Old Steve]

I can't see well in your pic, but you'll need to check whether one or the other of the switch contacts on the PCB connects to either +V or GND. Often, the contacts will be wired into a 'matrix', with neither contact connected to either ground or +V. If this is the case, your switch element will need to be 'floating'. Perhaps your oscillator will need to switch a CMOS switch across the contacts. A CD4016, CD4066 or similar. (A 4066 is the better choice of those two - it has a much lower 'on' resistance.)
https://www.fairchildsemi.com/datasheets/CD/CD4066BC.pdf

If one of the contacts is connected to either +V or GND, it's still best to use a transistor driven by the 555 to do the actual switching. (Open collector output.)