View Full Version : Microphone input

02-09-2007, 04:25 AM
Any ideas on how to convert the amplitude from a microphone or line sound source to a stamp?
I would need a variable that altered with the relative volume, kind of similar to a VU meter.

Another problem I am having with this project is I seem to have 'dirty' supply lines.
The circuit is suffering random triggering and I am sure it is noise on the 0v line.
The stamp and several other parts of the circuit are running through a 7805
I have diodes on the supply lines and a 22uF across the supply. What else can I do to smooth the supply?
It shares its feed with a cooling fan (and I can't seperate them).


02-09-2007, 04:51 AM
Put a capacitor across the cooling fan leads. With noise filtering, it matters where you attach the capacitor. The connection should be as close to the noise generator as possible -- in this case, across the fan leads AT the fan itself.

Read the 7805 documentation, as they recommend both an input and an output capacitor near the 7805.

Then you should have an additional .1 uF capacitor near the BS2 supply lines.

Sometimes it's good to parallel a .1 uF and a 10 uF at the same point -- the smaller capacitor handles higher frequency spikes, while the larger capacitor handles the lower frequency noise.

Mike Green
02-09-2007, 04:56 AM
You need additional filtering on the power supply line, at least several hundred uF. Get yourself a 1000uF or several 470uF 6-10V electrolytic capacitors and place them across the supply line. Be sure to also have a couple of 0.1uF bypass capacitors, one at the regulator and one at the Stamp if they're not already there.

If you want the average amplitude of the sound, you need a rectifier and filter to give you an analog voltage proportional to the sound level. The "Basic Analog and Digital" tutorial from the Parallax website will give you information on how to read this using a Stamp, but you'll need the analog end. Here's one discussion of a peak/VU meter. The Stamp would basically replace the meter: sound.westhost.com/project55.htm (http://sound.westhost.com/project55.htm).