Connecting an ext digital microphone to the LPC54114 Xpresso board

[jameswhitney]

Greetings I have the LPC Audio and voice Recognition kit which is an LPC54114 base-board with a MAO shield. I have looked at the schematic for the shield which shows three jumpers installed on P1. These jumpers connect 'VDD', 'CLK', and 'DAT' from the on-board digital mic to the MCU. Upon further examination it appears that these three jumpers could be removed and a different digital directly connected to Header P1, pins 1, 3, and 5. I tried this and it failed to work. I also noted that when the jumpers are removed, LED D2 *does not* illuminate which to me is an indicator that one of the signals - my guess being VDD feeds through and goes *beyond* just the microphone.

Can someone please provide some enlightenment ?

Thanks, and regards,

Jim

[brendonslade]

Hi James,

The mic you are trying to use is an i2s DMIC but the interface is for PDM DMICs. An different Knowles DMIC like SPH0644LM4H-1 Cornell should work.

regards,

Brendon

[jameswhitney]

Brendon,

Appears our responses crossed in the mail.

You are correct.

Thanks for the help

[brendonslade]

P1 just connects from the expansion connector (to the board into which the shield is connected) to the DMIC, just as you described:

The intent here is that you can either use the pins that receive DMIC data for another purpose, or connect a different DMIC, assuming you modify the software driver to suit that mic. 

I'm confused by your reference to D2; the shield doesnt have any LEDs and the LPCXpresso54114 board D2 is the user LED...?

[jameswhitney]

Good morning, Brendon,

Thanks for your quick response.

I don't think anything needs to be modified on the software side; the mics are from the same Knowles series, i.e., the on-board mic is the SPH0641. The mic I am testing is a SPH0645. The same 3-wire connection, just different sensitivity.

You are correct - D2 is not on the shield - it is on the LPC54114. The 'Red' section of D2 the tri-color LED, is used by the I2S dmic demo to indicate audio/acoustic activity and its brightness is correlated to the acoustic signal. 'MAYBE' the mic IS the end terminal of that bit of circuitry and D2 actually derives its actuation from some feedback of the data stream, unsure at this point. When I remove the three P1 jumpers and plug in the 0645, D2 is totally dead. If I remove the 0645 and reinstall all of the P1 jumpers everything operates as it should, so, nothing has happened to the board.

Maybe the 0645 is dead. Should have been simple enough, but I'll pull out a scope, plus I have another SPH0645. I'll wire that up and retry.

Thanks,

Jim

[jameswhitney]

OK, pulled out the scope.

Turns out that while part of the same family, the SPH0641 is a PDM output. The SPH0645 is I2S. It appears I need to make the correct connection into either header J1, or, J2.

Jim