Prototyping the MAX9814 automatic gain control microphone amplifier IC.


Not wanting to wait for a breakout for this IC I attempted to dead bug it instead. This IC is extremely small, at 3mm X 3mm and with 14 pins it looked somewhat daunting. From the pic you can see that it turned out fairly well. There’s really no point in being afraid of SMD parts, here’s a couple of tips:

  • Tint the pads on the IC before trying to solder to it, the idea is to tint both the pads and the wires and using flux simply sticking them together.
  • When working with IC’s this small if you can see solder on your iron tip you’re using too much. The ideal is when it looks like the solder didn’t stick to the tip but stayed on the roll.
  • Use lots and lots of flux, it’s cheap and makes it work, enough said.
  • Don’t go for the smallest soldering Iron tip you can find, the solder doesn’t sit near the tip nor does the heat transfer well to it.
  • Work from one pin to the next in sequence, don’t get trapped trying to solder a pin with wires already on both sides.
  • Don’t fix, remove the wire completely (and possibly wires on surrounding pads), clean up the pad if needed and start from scratch.

More on this chip to follow, this will hopefully turn into a small audio spy bug that will most likely be released open source. Happy hacking.

These are incredible little chips, on the highest gain setting it can pick up the smallest of sounds on the other side of the room. Be warned though, they tend to pick up lots of junk when built on a breadboard like this. This isn’t limited to audio but to breadboard wire placement etc. My bug did eventually die but not till I played around with it for a bit. I used the default schematic given in the datasheet:

This could easily pick up any audible sound though the bench power supply right next to it had a somewhat obnoxious fan that drowned out a lot of it, use battery power if possible. Here’s a screen of some music about 30cm away, it was playing fairly softly.

And a pic of the setup because I can 🙂


~ by s3c on 2012/07/17.

3 Responses to “Prototyping the MAX9814 automatic gain control microphone amplifier IC.”

  1. I like to build this circuit.I need to pick up DTMF tones appox 10ft away from
    its sound source. Which would be the best settings 40db,50db,or 60db to get me the 10ft i need.But with out adding noise to the circuit.The room is fairly quiet.

    • The great thing about DTMF is that it’s fairly immune to noise. I would set the gain to 60db and let the DTMF decoder deal with the noise. Remember that the AGC IC controls the gain to keep the signal from clipping, meaning your SNR is fairly good over a wide input range. If for some reason you want to the signal as noise free as possible set the gain to 50db or 60db and use a comparitor and 555 for a squelch type circuit.

      • Can you draw me a circuit for a comparitor and 555 for this squelch circuit.And how would this be connected to the max9814.I would appreciated this.

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