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[on:]

I've fed the ArduinoBT with 3 9V batteries (parallel connection) and a lm7805 voltage regulator (this thing keeps the output voltage at 5V - http://www.eidusa.com/Electronics_Voltage_Regulator.htm)

Before that I was powering the board with just one 1,5V battery for some simple tests.

I noticed that the board does a strange noise with the 9V batteries, that didnt happen with the 1.5V baterry.

Is this normal? Do your boards make any noises at all?

I connected the 3 9V baterries in order to get more current power (more mAs) coz the 1.5V batteries didnt last for long. Do the boards work with specific current values(mAs)? The main site didnt say anything about mAs for the BT board  

[Reply #1 on:]

The ArduinoBT has a switching regulator on it which will make noise. This is normal, and is expected that the noise will be different at different input voltages. Most likely the design uses multi-layer ceramic capacitors (MLCC) which are notorious for "singing".

Note that you are really wasting a lot of power by converting 9V-->5V. I think you will get much more life out of your batteries by powering it with three 1.5V batteries in parallel.