Electronics > Projects, Designs, and Technical Stuff

HX711-based milliohm meter

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dannyf:

--- Quote ---you should obtain resolution of 0.5 milliohms which is pretty impressive.
--- End quote ---

Not quite there but I can get to about 5milliohm resolution easily. The update rate is faster than my eyes can process, :)


--- Quote ---I haven't tested this though, so I may have missed or overlooked something.
--- End quote ---

you are spot on.

I built a current generator out of it, if you are interested: https://dannyelectronics.wordpress.com/2015/11/12/a-digitally-controlled-current-generator/

Those tiny AVRs are simply amazing.

Kalvin:

--- Quote from: dannyf on November 15, 2015, 05:27:50 pm ---I built a current generator out of it, if you are interested: https://dannyelectronics.wordpress.com/2015/11/12/a-digitally-controlled-current-generator/

Those tiny AVRs are simply amazing.

--- End quote ---

Nice gadget! I haven't been using those small AVRs yet. The Atmega328 seems to be a bit limited in the ADC compared to the Attiny85. I did something similar as built a battery capacity tester a while ago, but used op amp in the control loop and the Atmega328 producing the current controlling voltage with the PWM DAC. I have a few STM32F103 boards and PSOC 5 boards, so hopefully I don't have to struggle with the Arduino and/or Atmega328 any more :)

dannyf:

--- Quote ---The Atmega328 seems to be a bit limited in the ADC compared to the Attiny85.
--- End quote ---

Very much so.

I worked on a milliohm meter using icl7107 (or the likes), down to 1mohm.

I'm working on another  utilizing mcp3550/3551: 22bit adc and quite inexpensive. Good down to uohm range.

The same strategy works for LTC2400 as well.

necessaryevil:
The Jan 1983 elektor contains two miliohmmeter circuits. The first is just a 100 mA current source, but the second one is a pulsed current source and a sample and hold circuit. Maybe an idea?

darksky:
Hi Guys,

I have played with the HX711 and can now read a resistor to an accuracy of better that 50 uohms or 0.0004% of readings.

circuit is 1500ohm resistors with reference as 10 ohms but it is important to place a 0.1 capacitor accross the reference resistor and DUT.

DUT range 0- 22 ohms

Thie capacitor greatly elimiates noise and increases accuracy.

I have also been able to write code for the arduino that allows measurement of a 10k resistor to an accuracy better that 0.5%.

The idea is to place a 10 ohm resistor as the DUT measure its value then place a an unknown resistor accross that, then calculate the effect of the unnown value.

I can now measure accuately from less than 2 milliohms directly and upto 10k with the parallel method. Accuracy at 10K is better than 2%.

Happy to share the code and circuit with any one interested.

Thees chips have a lot of potential.

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