How to accurately measure the current drawn by my display using Teensy Analogue in

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Experimentalist

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Can anyone advise the best way to measure the current drawn by my display using an analogue in pin?

The expected current is in the range 400-500mA, I am using a Teensy 3.1, so 3.3V analogue input tolerance.

As I see it if I used a 0.1 ohm shunt and the display consumed 400mA I would only be getting 40mV and therefore would be getting very poor accuracy considering what can be measured, that is 3.3V max.

Am I right in thinking the following?

400mA through 0.1 ohm shunt I would get:

400mA x 0.1 ohm = 0.4 x 0.1 = 0.04 = 40mV

(40mV / 3.3V) x 100% = (0.04 x 3.3) x 100% = 1.21%

So I would only be using 1.21% of the ADC resolution?

There must be a better way, probably many, but is there a simple solution? Off the shelf?

Anyone?

Ex.
 
at 40mV, you need to use one of the ADC channels that can use one of the K20's gain amplifier. Teensy has such. AVR mega328 does not. Mega1284 does.
 
If you use the differential and the PGA you can get a full scale of 1.2 V/PGA, where PGA=1 (disabled), 2, 4, 8, 16, 32 or 64. PGA uses always the 1.2 V internal reference, so you have to activate it too. With a PGA of 16 you get a full scale of 75mV so your signal of 40mV is more than 50%.
 
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