JStat60 0 Posted June 7, 2017 Share Posted June 7, 2017 Hi, I have a non-profit (Smoky Mountain Scientific, smokymtsci.com) that develops and sells low cost instruments for science education. One of our instruments incorporates a Tiva-C launchpad that outputs a pwm voltage and measures voltage and current passed in electrochemical reactions. I recently purchased a fairly large batch of Tiva launchpads from Mouser and I am having trouble with noise in the analog read channels for about 1/4th of the boards. We have been building and selling these instruments for a couple of years now and have never had this problem before. To test the boards, I send a pwm signal through a simple low pass filter (a resistor and a capacitor) then read the output on two channels (A11 and A8). The attached figures show examples of output from a good (file Board46) and a bad (file Board37) boards as displayed on our user interface. This seems to be a hardware problem and I dont know how to go about resolving it. Any recommendations? Thanks, Jack Quote Link to post Share on other sites
PTB 27 Posted June 8, 2017 Share Posted June 8, 2017 Are the good ones and the bad ones using the same power supply? I was getting "wobbly" adc readings due to a cheap power supply. Problem went away when I used a more quality power supply. In my case an iPhone charger. Cheers PTB Quote Link to post Share on other sites
JStat60 0 Posted June 8, 2017 Author Share Posted June 8, 2017 Thanks for the suggestion @PTB but I dont think that is the problem. I am powering these through the USB port on my computer. I am also using the same micro USB cable and there is no change in the quality of data between trials. That is, a good board will always give good readings and a bad one will always give bad readings. Jack Quote Link to post Share on other sites
PTB 27 Posted June 9, 2017 Share Posted June 9, 2017 Hmmmm then I'm out. That's all I got. Does kinda sound like a bad batch. Quote Link to post Share on other sites
spirilis 1,265 Posted June 9, 2017 Share Posted June 9, 2017 I see you posted an E2E thread for this, that was my only suggestion (interesting to see what TI says about this) https://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/t/601521 Quote Link to post Share on other sites
JStat60 0 Posted June 9, 2017 Author Share Posted June 9, 2017 That was a good suggestion @spirilis, I posted on the E2E site on the recommendation of the folks at Mouser. Had they not recommended this (and you as well), I would not have done so. The conversation on the E2E site is very helpful. Thanks, Jack Quote Link to post Share on other sites
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