On 12/17/2018 5:09 AM, andy pugh wrote: > Not as on-topic as I would like, but I suspect that some of you here > might know something useful. > > I am trying to interface an ADS1256 board to an Arduino. > https://www.ebay.co.uk/itm/19242863594 > > Sometimes it almost works... > It will often sit there reading all-zeros then suddenly appear to > work, to an extent. But I don't seem to be able to configure it for > single-ended so suspect that the programming instructions are not > getting through. > The fact that the data output comes and goes makes me suspect that the > SPI comms is iffy. > > The connection runs via the IO pins of an Arduino Nano,rather than > using the ICSP connector. > > If I touch the ICSP connector on the Nano with my finger then the data > switches to 0xFFFFFF
That sounds like a floating signal. > So, I am wondering if the SPI bus needs to be terminated or something? Generally not...more below. > Also, the board has 100 Ohm resistors in series with all digital IO, > but the ADS1256 data sheet only shows 100R resisitors on the input > channels. Is this likely to be worth changing? Leave the resistors. They are series termination to limit current spikes during edge transitions, which can otherwise interfere with the ADC readings. They basically slow down the edge rates, which shouldn't matter unless your clock frequency is *VERY* high and/or you have a long cable with lots of capacitance between the boards. > I have used other SPI devices with the Nano, and have not had these problems. > I have also tried with a full-size Arduino, with equally limited success. > > Any tips for robustification of SPI comms? Double-check your wiring and the data sheets, paying particular attention to the direction of the data signals. I have found the data line labeling (MISO/MOSI, DIn/DOut, etc) to be somewhat haphazardly applied, and your symptoms would be explained by having the data lines swapped (so two drivers bus-fighting on one line, and the other line floating). -- Charles Steinkuehler char...@steinkuehler.net _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
