TM4C ADC 0 Fluctuating Readings

While your name is (surely) a good & interesting one - it may not serve as an ideal "identifier" - for the subject matter you present here.

In your case - might, "Fluctuating ADC reading w/TM4C1294" better reflect your "Subject?" Knowing your area of "tech interest" enables others to determine, "if and how" they may assist you.

This class of MCU (from any vendor) is not known for excellent accuracy & precision - thus (some) fluctuation of reading is expected. As always - "devil is in the detail" - and you have not provided any insight as to what you define as, "very fluctuating."

Your presentation of your ADC code would prove useful - as well. Best ADC readings are achieved when the output impedance of your analog front end - nicely matches the input impedance of the MCU's ADC. (a good read of the MCU manual further details...)

Another source for fluctuating readings is the supply.

Analog readings compare the voltage difference between their input pin and their GND pin to the voltage between their reference voltage and their GND pin. Now the momentary GND level on the MCU is not necessarily the same as the momentary GND level on the analog signal source. Especially A/D converters built into an MCU suffer from the ripple current generated by the MCU core. It introduces a pulsating voltage drop along the GND path between the MCU GND, the analog signal GND and the supply GND level.

Some MCUs provide a separate analog GND (and analog VCC) supply pin. These must not be connected to the digital GND/VCC. The VCC shoudl be at least separated by some sort of filter (e.g. a series resistor and between digital and analog VCC and a capacitor between analog VCC and analog GND). The analog gnd should be routed separately form the digital GND and meet the signal source gnd somewhere (e.g. directly at the supply) so that no MCU operating current flows through the analog GND traces.

On MCUs without a separate analog GND, the GND traces should be as big and straight as possible (to minimize voltage drop by minimized resistance and inductance). And the supply should be filtered by blocking coapacitors as close to the MCU as possible: large electrolytic ones (or tantalum) and smaller but fast ceramic ones together. 10µF ceramic capacitors are available for 6.3V on 0805 size and do a very good job.

Jens - so good to note your return! (even though brief)

We suspect that you've visited your (old) haunts as well (MSP) - that likely proves wise as this poster has "gone quiet" (but for removing his name from the post's Subject line) and one week will have passed since his (only) arrival here.

Best of luck to you - know that you ARE missed and are wished well. (Do you read your forum "messages?") Bye...

cb1_mobile said:

Jens - so good to note your return! (even though brief)

I've never been completely away (except fo rthe last two weeks in which I didn't have any internet access - or at least didn't want to pay a fortune for every single MB). I just don't scan the forum for new threads anymore. But I still receive mail notifications for new posts in threads I once participated in. And sometimes I answer.

However, I posted here because this thread was mentioned in the MVP forum (where I'm still active, on a low level)

AFAIK, the subject line was changed by a staff member. Maybe this action has kicked the thread out of the focus of the OP.