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FRDM-KL25Z input from ADC output to DAC

Question asked by Nicola Lacalendola on Mar 13, 2014

Hi guys,


I'm trying to acquire waveform (sinewave in this case) by using the ADC then output them right away through the DAC. So what I'm expecting is identical, or at least very similar waveforms on the oscilloscope. I have attached my results so that you guys can have a look, it is very far from expectations.


ADC set up:

Core and Bus Clocks: 20.99072 MHz

A/D resolution: 12-bit

Conversion Time: 7.692308 us

Sample Time: 20 = long

Number of conversions: 32


DAC set up:

D/A Resolution: 12-bit

Data mode: unsigned 16 bits, right justified

DMA, Interrupts, Hardware Buffer NOT USED.


Things I have tried:

Different sampling time, different conversion time, different number of conversions. different resolutions, feeding input via unity gain buffer (in reference to this: ADC Stability).

I am certain that the DAC works fine as I spent quite a lot of time troubleshooting it (FRDM KL25Z DAC Overshooting).


I suspect the ADC is acting up somehow but I haven't quite figured out yet as don't know how to visualize the values I am getting(UART.rar is my attempt of doing so). I have attached my project files as well (ADCin_DACout.rar) .


Thanks in advance guys.


Original Attachment has been moved to: UART.rar

Original Attachment has been moved to: ADCin_DACout.rar