ACSR Voltage Divider

Other Hardware General Electronics
1

In this example http://www.gammon.com.au/forum/?id=11916 , it is using a voltage divider for ref & input, whereas the component i am using is a thermal based divider. Were (f) is an etched, fixed resistance value & (v) is a silicon oxide variable resistor.

+5v--->resistor(f)--->resistor(v)--->GND
|
|
|
(mv_output)

Therefore this would negate a second stage divider, but my real question is , when using the ACSR, would using such a device as a reference voltage be a problem as its (mv_output) may fluctuate?

2

You are referring to this image?

456×516 2.11 KB

Can you label your resistors (R1/R2/R3 etc.)?

What do you mean "a second stage divider"?

3

You can not use a referance voltage of less than 1V on an arduino.

Referance voltage fluctuation will result in reading fluctuation for a steady input voltage.

4

Where AIN1 is the reference voltage to be compared to AIN0 incoming voltage.

I will reword my question, what is the time measurement (micro/nano) where AIN1 is read & AIN0 is compared?

5

Grumpy_Mike:
You can not use a referance voltage of less than 1V on an arduino.

I'm not convinced that limit applies to the analog comparator.

Trying a small test:

ISR (ANALOG_COMP_vect)
  {
  PIND = _BV (2);  // toggle D2
  }

void setup ()
  {
  ADCSRB = 0;           // (Disable) ACME: Analog Comparator Multiplexer Enable
  ACSR =  _BV (ACI)     // (Clear) Analog Comparator Interrupt Flag
        | _BV (ACIE);    // Analog Comparator Interrupt Enable
  pinMode (2, OUTPUT);
   }  // end of setup

void loop () { }

With a pot on D7 to adjust the reference voltage I got it down to around 100 mV, and still the output pin (D2, yellow trace) toggled which means the analog comparator got a match:

6

JB_AU:
I will reword my question, what is the time measurement (micro/nano) where AIN1 is read & AIN0 is compared?

The comparing would be almost instantaneous (one clock cycle, say), however it takes around 2 uS for an interrupt routine to get underway.

7

Thankyou

8

Grumpy_Mike:
You can not use a referance voltage of less than 1V on an arduino.

The minimum for Vref is quoted as 1V, however that is under the ADC section (page 323) and not under the Analog Comparator section.

9

Yes sorry I thought you were talking about the A/D.