# Full Duplex Intercom

#### mark63534

Joined Nov 24, 2011
20
Here is the link to the schematic:

Rich (BB code):
http://www.redcircuits.com/Page78.htm
On the website it says that the recommended power is between 6 to 12 volts, at 200mA. Now, it's not that easy finding a power supply for that amperage. So my question is, can I simply jjust use two 9v batteries instead of using a power supply that is hard to find?

On top of that question, I have another. How would I hookup a computer microphone to this setup (assuming that the output configuration is a 3.5mm jack) ?

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#### MrChips

Joined Oct 2, 2009
23,121
What do you mean? Most wall warts will fit the bill. It doesn't have to be 200mA.

#### mark63534

Joined Nov 24, 2011
20
What I'm saying is that I have a computer power supply near me (actually a molex connector used for computer power supplies) and I would like to use that. However, the rating for that power supply is 12v @ 1.5A.

I'm pretty afraid that if I use that to power both circuits, they might just fry. Why? Because on the schematic it says to use 200mA.

So, would they get fried or would the circuits just draw enough for operation?

#### BillB3857

Joined Feb 28, 2009
2,543
The 200ma referred to in the schematic is how much the device needs to operate. It will only take what is needed. The battery in an automobile is capable of providing hundreds of amps. Does your car radio go up in smoke when you turn it on? No. It only take as much power as it needs as long as the supply voltage is what the unit is designed to use.

#### MrChips

Joined Oct 2, 2009
23,121
But before you use that 12V power supply, measure the output voltage. If it is unregulated the unloaded voltage can be 15V.

#### SgtWookie

Joined Jul 17, 2007
22,221
the 200mA specification is the minimum supply rating.

The supply can be rated for much more current and it'll be OK.

Just don't exceed ~14v in and you should be ok.

Use 200mA or 250mA fuses.

#### mark63534

Joined Nov 24, 2011
20
Wow. Thank you so much. I will definitely take that into consideration when making this, and I will be checking my power supply asap.

#### mark63534

Joined Nov 24, 2011
20
I have a second question:

In the schematic, there is a P1 which is a 22k Log. Potentiometer. I can't find any of these ANYWHERE. So, can anyone tell me where I can get some of these?

Or, will a 25k Log. Potentiometer suffice for the job?

Thanks.

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