[SOLVED] Potentiometer using ADC

[vilfred]

Hi,
I am searching a formula/concept to measure the resistance of Potentiometer through ADC of microcontroller. I'm using 10-bit ADC and +5V microcontroller, but not a fixed potentiometer (potentiometer may be of different values such as 10K,1K,100R). My project is to measure 80% and above of any potentiometer resistance, where above 80% should be indicated through LED. How it is possible to measure?
Formula i've taken is, digital value= (voltage output/drop * Maximum ADC value)/total voltage
From this formula i calculated the 80% of digital value, for eg. i assumed 80% of total voltage first for substituting i.e. voltage output = 4V, Max ADC value = 1024(2^10), total voltage = 5V
When substituting it in digital value formula i get 819.2
So Whether it is correct to written a condition as

if adc_read value is above 819.2
{
led_glow;
}
else{
led_off;
}

or is there any different formula or concept available. Please give me some suggestions and clarifications

 

[baileychic]

You can connect a ACS712 current sensor in series with Potentiometer. The ADC0 channel will then provide voltage across the measured resistance and the ADC1 will give the current through the resistance. With V and I you can calculate R of the POT.

 

[KlausST]

Hi,

* no need to know/measure pot_total_resistance.
But it's important to use this setup:
* connect one end of the pot with GND
* connect the other end of the pot with VCC (ensure clean properly decoupled VCC)
* connect the wiper with ADC. (A decoupling capacitor to GND could help to reduce noise)
* use VCC as ADC_VRef

Then (independent of pot_total_resistance) 80% of pot will result in 80% x 1024 of ADC_value = 819 (rounded to next integer value).
The use of float value makes no sense.

Thus your concept was (almost) correct.

Klaus