Can't run cn0554_example.py

Question

Hi Everyone, 
 I am directly interfacing the CN0554 to an RPI4 running ADI-Kuiper-Linux OS. I followed the instructions in https://wiki.analog.com/resources/tools-software/linux-software/pyadi-iio to install pyadi-iio. 
 After that I downloaded the example https://github.com/analogdevicesinc/pyadi-iio/blob/master/examples/cn0554_example.py and tried to run it, but I get the error below 
 Traceback (most recent call last): File "/home/analog/code/cn0554_example.py", line 17, in <module> my_cn0554 = adi.cn0554(uri='local') AttributeError: module 'adi' has no attribute 'cn0554' 
 
 Has anybody else run into this error? 
 Thanks, 
 Massimo

Massimo44 · Accepted Answer

Hi Dragos, 
 Thanks for your reply. I am out of town now, but I will try your suggestion as soon as I get back. 
 Regards, 
 Massimo)

MarkThoren · Answer

Hi Massimo44 , I'm not the Linux driver expert but I do have some experience working with the AD7124 and its pyadi-iio class. Fundamentally, it may not be possible to achieve continuous streaming data with the Raspberry Pi, limited by the SPI peripheral and how quickly it can respond to interrupts. We do have designs that capture high sample rates over a serial SPI interface, but they typically use the SPI engine (see https://wiki.analog.com/resources/fpga/peripherals/spi_engine) which requires an FPGA. 
 Note that the AD7124 is not specified for measuring AC signals (where you'd quantify THD, SNR, etc. with a sinewave applied.) And it's not possible to truly synchronize the sampling with an external event, at least not with the present incarnation of the driver. There is a SYNC pin, but I'm not sure if that will confuse the driver, nor how it would affect operation when multiple channels are involved. That would be a question for Linux Software Drivers . 
 As another tangible experiment, in this article: https://www.analog.com/en/technical-articles/use-python-for-analysis-of-noise.html we had to throttle the sample rate to 64 sps to guarantee no missing samples in the data records used to plot the filter response. 
 Another point - While the AD7124 is capable of running at a base sample rate of 19.2 ksps, whenever you enable multiple channels, this is not only split across the channels, but an additional number of samples are required to flush the digital filter - for example if the SINC4 filter is selected and two channels are enabled, the effective sample rate per channel is the base sample rate divided by 8. 
 To summarize - the AD7124 is mainly suitable for DC measurements, or signals that move slowly such that a one-sample delay in reading data (caused by a missed data point) won't affect overall operation. 
 andieo is working on another pyadi-iio class for a power supply board that uses the CN0554 as a controller / monitor, and I've recommended to NOT use rx(), rather use raw * scale + offset (with some additional scaling that applies to the board it's attached to.) The original intent was to use rx() to capture a buffer of samples, then average them. But the AD7124 already does this - setting the sample rate to a lower value inherently averages more, has a narrower filter bandwidth, and correspondingly lower noise. 
 If you do need to characterize quickly moving signals, the AD7768 family (single, quad, and octal) of sigma-delta ADCs is an option - but requires an FPGA to receive the data. Depending on how fast the signals are moving, a SAR (sampling) ADC may be more appropriate. 
 -Mark

Partner Forums

Partner Libraries

Products Mentioned

Associated Drivers

Associated Drivers

Associated Drivers

Can't run cn0554_example.py