Hi David: I think it is a hardware problem.
It looks like you are not doing a good job referencing your ground input for the ADC, or you have a very dirty Voltage reference for the ADC. Either way, it is picking up some serious offset from a switching power supply (The PMMIC ???) somehow. I think you need to do an audit of the power going to the Voltage reference for the ADC, and the connection of the positive and negative Voltage references, and the negative input on the ADC. --- Graham == On Wednesday, February 8, 2017 at 6:34:37 AM UTC-6, [email protected] wrote: > > Hi, > > I adapted the code from Derek Molloy example - > http://exploringbeaglebone.com/chapter13/ - > https://github.com/derekmolloy/exploringBB/tree/master/chp13/adc - to > read this adc - ad4000 - > http://www.analog.com/media/en/technical-documentation/data-sheets/AD4000.pdf > with a 500kHz sampling. > The only thing i changed, according to communicate with this adc, is that > i read 16 bits on the PRUADC.p and TIME_CLOCK is 1 (12.5Mhz for SPIclock). > I'm not an assembly expert, so i really can't figure out the problem. > > I tried read the this adc from the SPI0 of BBB(using Derek Molloy exampels > too http://exploringbeaglebone.com/chapter18/) , of course not with a > 500kHz sampling, just for test, but the problem is the same, i'm working on > this for more than 4 weeks, and i can't solve the problem, and is not a > hardware problem. > > In this examples, i have in the analog input of the adc, a square wave(3.3 > V), and 3 constantes voltages(680mV,1.8V,3.3V), all examples done on PRU, > and this are the results: > - Y axis -> Volts > - X axis -> Number of sample > - Vref of the adc is 4V. > > > <https://lh3.googleusercontent.com/-XwrjqFvVtGg/WJsEk4j8sKI/AAAAAAAAABs/syvlHagqHk0CB5y-At3JbOmMsNLpl5n3gCLcB/s1600/pwm.jpg> > > > <https://lh3.googleusercontent.com/-80w756WyytI/WJsEsYqOe9I/AAAAAAAAABw/h0BMszD018gyhgLIMas88OlLQnqCDESvwCLcB/s1600/0.68.jpg> > > > <https://lh3.googleusercontent.com/-r4FQ7bbvFB0/WJsEvqIAe8I/AAAAAAAAAB0/0CGjj9MW2iMwUHA3KXuos2TumCYwEONtgCLcB/s1600/1.8.jpg> > > > <https://lh3.googleusercontent.com/-_5RdOLgXL6E/WJsEyV_cEnI/AAAAAAAAAB4/RzwEyv3SBPM6hUX1LT6yNFbJJ0bk-gB2ACLcB/s1600/3.3.jpg> > > > > Any help would be aprecciated. > > Best Regards, > David > > > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/b94014a1-7158-4dee-a304-edab41c21e4d%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
