topic Re: DAC_UpdateValue in LPCXpresso IDE

DAC_UpdateValue

lpcware — Wed, 15 Jun 2016 21:40:57 GMT

Content originally posted in LPCWare by dmorton on Sun Feb 03 21:29:35 MST 2013
I am playing with the demos for the Embedded Artists base board, in particular the demos that emit sounds through the speak - speaker_wav primarily.

The speaker_wav project is pretty basic, passing an unsigned byte into DAC_UpdateValue at 8000Hz.

The inline documentation for DAC_UpdateValue in lpc|_17xx_dac.c indicates that the second parameter, the value parameter, is a 10 bit value.

What is strange is that the speaker_wav project passes an 8 bit value into DAC_UpdateValue, and if I modify the project to scale up the 8 bit values to 10 bit values, no sound is emitted. If, on the other hand, I scale down the 8 bit values, I just get softer sounds.

In http://www.embeddedartists.com/sites/default/files/support/xpr/base/LPCXpresso_BaseBoard_rev_B_Users_Guide.pdf there is no mention of driving the speaker with a DAC, only with PWM.

Im wondering if perhaps the DAC is emulated by PWM and limited to 8 bits rather than 10 bits?

Re: DAC_UpdateValue

lpcware — Wed, 15 Jun 2016 21:40:58 GMT

Content originally posted in LPCWare by dmorton on Sun Feb 03 21:50:27 MST 2013
Oh yeah, again because the DAC output appears to be undocumented, if it is indeed supported at all, where on the Embedded Artists board would I connect headphones to?

Re: DAC_UpdateValue

lpcware — Wed, 15 Jun 2016 21:40:59 GMT

Content originally posted in LPCWare by dmorton on Sun Feb 03 22:20:36 MST 2013

Quote: dmorton
Oh yeah, again because the DAC output appears to be undocumented, if it is indeed supported at all, where on the Embedded Artists board would I connect headphones to?

Hmm, looks like I disable jumper pin J32, and then pick up the signal across jumper pins J34.

And.. it appears that references to PWM audio are in fact DAC audio, at least when coming from the 1769 board which has a DAC.