Hi there,

I'd like to drive an 8 ohm speaker from the mbed DAC. Can anyone recommend a circuit I can buy/build to do this, powering from the 5v USB out? Or will I need an external power supply :(

Kind Regards,
Mike

Hi Mike,

I used the Maplin 1W amplifier kit N48FL at a fiver which has far too high a gain, but referencing the LM386 spec you can easily figure out which components to leave out to reduce the gain a bit and use a series resistor with the input pot to bring it down to unity(ish) gain.  This may be the hard way to do it but I have a Maplin store round the corner and it saves thinking too hard!

Regards,
Pip

Hi Pip,

Ah, sounds like a convenient little kit to canabalise. I noted that the LM386 is the amp that Keil use on the Eval board for the LPC2378, so I guess the circuit is tried and tested: http://www.keil.com/mcb2300/mcb2300-schematics.pdf

Comparing it with: http://www.maplin.co.uk/Media/PDFs/N48FL.pdf
I had a look at: http://www.national.com/ds/LM/LM386.pdf

It seems that as soon as you put a capacitor between pins 1 and 8 (as in the Maplin kit) the gain goes up by around 10x ... so you might want to leave pins 1 and 8 unconnected, i.e. dont fit R1 and C3. Looks like a coll little kit for £5... especially now it is so easy to play WAV files from and SD card... think I'll have to stop by Maplin
tomorrow :-)

Cheers,
chris

I have today mended an old discrete component Transistor Radio (a treasured favourite) with an 8-pin DIL chip from Maplins.  Maplin code UK79  chip code TDA 7052

Works a treat. No bulky capacitors fro the LS, it just works.

http://www.maplin.co.uk/module.aspx?moduleno=2226

JF