# Circuit for low power consumption 8.2k resistor comparator

#### renatopinheiro

Joined Mar 21, 2019
5
Hi,

I'm trying to develop an 8.2k resistor(8k2) comparator pin. What is the best way to do this with low current consumption?
I try with a voltage divider but it gave a high consumption because even just reading the pin a few times per second, the R5 is connected to the GND and consumes all the time that the 8k2 resistor is connected.

Voltage divider circuit:

This give me a consumption of about 0.4-0.5mA. I need a consumption below 0.05mA.

What is the best technique to use in this case?

Best regards.

#### Alec_t

Joined Sep 17, 2013
11,627
Welcome to AAC!
You could charge/discharge a capacitor via the resistor and measure the time taken to charge/discharge. The average current would be very small if the time between successive measurements is long.

#### crutschow

Joined Mar 14, 2008
25,367
Why does it have to be 8.2kΩ?
Can't you use a larger resistor?

Can you use a shorter measurement time?

#### mvas

Joined Jun 19, 2017
537
Can you increase the value of R5 to 100K ?

#### mvas

Joined Jun 19, 2017
537
Make a 0.05 ma Constant Current Source
Connect the 8,200 Ohm Resistor across the output
Turn ON the CC Source
Measure the Voltage using the ADC
Turn OFF the CC Source

0.41 Volts = 0.05 ma x 8200 Ohms

#### renatopinheiro

Joined Mar 21, 2019
5
Why does it have to be 8.2kΩ?
Can't you use a larger resistor?

Can you use a shorter measurement time?
Hi crutschow,

I can´t use a larger resistor because the place of the resistor will be an automation safety edge bands that use 8.2kΩ.
I need to take very measurements per second because of safety reasons.

#### renatopinheiro

Joined Mar 21, 2019
5
Can you increase the value of R5 to 100K ?
Hi mvas,

If I do that I will lose resolution on the measurement.

#### renatopinheiro

Joined Mar 21, 2019
5
Welcome to AAC!
You could charge/discharge a capacitor via the resistor and measure the time taken to charge/discharge. The average current would be very small if the time between successive measurements is long.
Hi Alec_t,

I need to measure 10-20 times per second for safety reasons.

#### OBW0549

Joined Mar 2, 2015
3,544
Instead of powering the resistor being tested directly from Vdd, power it from an I/O pin on your processor. When taking a measurement, first set the pin high then trigger your ADC conversion. When the ADC conversion is done, set the pin low again until the next measurement cycle. That way, the voltage divider will only draw current for a brief period during each measurement cycle.