Thanks so much getting back to me. Did you get my user name – Ted's Dad! As it's for Ted I thought it was fitting to choose this username – any enough of my eccentricities!
Okay, I'll try and work through your questions.
Yes, I have both the 1w mono amp and the 20 second digital voice recorder / player (I'll refer to it as DVR). Presently they have their own speakers and battery packs.
You're diagrams are very close to what I want to do – impressive. I've attached images of the modules I'm trying to use.
More info:
The amp, has a jack input / output for mic (I've added a jack plug) and speakers.
The DVR has a 40mm mylar speaker attached, button for record, button for play, an LED to indicated playback and a battery pack. I plan to keep the mic and the record button so Ted can change the sound. This will all be made much more compact.
Ideally, what I'd to do is run both modules from a 9v battery. This would require a voltage regulator to step down to the DVR. The amp can still run at 9v.
Next, I'd like the speaker output leads from the DVR to be connected to the output jack of the amp (maybe with an inline pot to control gain). I then just have one speaker. I can then independently control the gain of the amp and the DVR. Why don't I want to route sound through the DVR? Well, the sound quality is not that great in the circuit. The amp is a really nice design and has a very clean input and output.
So, to recap. When sound plays through the amp, nothing happens with the DVR playback. When the amp becomes silent or music / speech stops playing, the DVR is triggered on the play contacts to make the sound. It would need to timed so it didn't last too long – maybe 300ms and it would then have to stop.
I did get the DVR pulsing sound by connecting the jack output contacts from the amp to the DVR play button contacts. Unfortunately, this is the reverse of my goal.
I thought it would be as simple as a resistor and a capacitor connected to the DVR play switch from the output jack terminals of the amp. It didn't work though. My idea was that the cap would store a charge and the release it when the amp output voltage ceased. What I forgot was that it is all AC voltage outputting from the amp (measured DC and nothing outputting from the amp). So, the cap wouldn't work for this, it would only smooth the voltage and allow it to pass through to the play switch of the DVR.
Does this all make sense? I'm trying to add just a couple of small components to do this – well in my world anyway. The real world maybe different. I need to keep it all very small for the application.
I thought about transistors to do it but I have no experience with them. Also, don't they need a DC voltage to trigger them?
The schematic is a bit beyond my present skill – I am learning and will continue to do so. BTW, a 555 chip came to mind – would this work with a transistor or miniature relay? I like the idea of a transistor as it is so small.
The plot thickens. Any more suggestions would be most welcome.
Cheers,
Rees.