Two PCBs off of one power source

[sherial]

hey,everyone
I am trying to run a FRS radio (3 AAA's) and a simple printed on board chip sound effects circuit board (generally 2 AA's, but will work with 3 AAA's it seems without frying it, and it gives me added volume which I needed), off of the same 3 AAA power supply. I was told to use a 10 ohm resistor in line with the power end of the sound effects PCB off the positive battery post, and I get reduced volume and distortion. I was then told to use a silicone diode, and that resulted in reduced volume, and the radio not working at all (the radio is not hooked to any of these components by the way). I also tried a Zeener glass diode, and that seems to have fried the receive end of the FRS amplifier. I have tried a few different values of resistor and I can only get low and distorted sound out of the sound effects PCB (mind you that I am over volting this thing, and it is still too quite). Does anyone know what I can use and where to put it, so both of these devices can run off of one power source? The sound effects PCB does not run continuously when the radio is powered on, but it will be used intermittently on occasion when the FRS is on.

Thanks for any help.

sherial

 

[panic mode]

standard Si diode has forward drop of about 0.7v. if you connect your radio directly to 3xAAA but your sound circuit through two Si diodes, you will drop voltage by 1.4V (for sound circuit only).

 

[()blivion]

It's as panic mode has said, with some minor details I would like to add.

Even with a dropping diode in line, if you are not drawing any current it *WILL* reach up to the peek battery pack voltage. If you know for sure the supply voltage will ruin your sound effects circuit, (you claim it doesn't) then you may need to use a high ohms shunt resistor to prevent over voltage. This resistor connects the batteries together AFTER the diode. Do note that this resistor will obviously put a small drain on the batteries constantly. Better methods would be a voltage regulator with super low quiescent current or a properly rated effects board.

If you have tested your effects board on 3 fresh batteries and it works fine, then I personally wouldn't sweat the power issues and would just hook them all to the same supply. 1.6 extra volts is not much really and the name plate Vmax for most things 3-3.3v is 4.5v. No guaranties it will survive, so i'm not recommending it of course, but I have made my 1.7 volt CPU run at 2.1V which is about the same jump and a much more delicate device. Another option is to run the radio off of 3 NiCds as they have 1.2v for each cell for a total of 3.6V. Then you get the advantage of lower voltage by default plus rechargeability. Finally, you can run it off a single Li-X, which will have the same effect as using NiCd's.