Internal Analog Reference - 1.1v & 5v in the same program

Projects Programming
1

Morning,

I've got a program that is using the internal 1.1v reference to increase the read resolution of an LM35 temperature sensor output using analogReference(INTERNAL);

However, is there a way for me to set analogReference to 1.1v on specific analog pins, and 5v on other pins?

2

No. It's one or the other.

You can, of course, switch between them at will though. Add a slight delay to allow the references to settle between each change.

3

I feared that would be the problem.... the dreaded delay.

Cheers anyhow!

4

The other option is to use an external ADC. Then you can have 2 voltage references - the one for the internal ADC, and a different one for the external ADC.

I am working on an ADC shield at the moment: http://hacking.majenko.co.uk/node/58 and in my testing of it I use the internal ADC of the Arduino to monitor the Vref of the external ADC.

5

I feared that would be the problem.... the dreaded delay.

It is not necessary to delay(). Simply discard the first reading after switching reference voltages.

6

It is not necessary to delay(). Simply discard the first reading after switching reference voltages.

Which basically creates a delay :wink:

7

Which basically creates a delay

Yes, but it is a delayMicroseconds (110) (approx), which is only a tenth of a "delay(anything)" :wink:

8

PaulS:

I feared that would be the problem.... the dreaded delay.

It is not necessary to delay(). Simply discard the first reading after switching reference voltages.

Simply discard the reading? Sorry?

What I meant, was to be able to simultaneously read the input from an LM35, whilst reading other 0 - 5v sensors - in addition to running numerous other I/Os. A delay of any sort is a delay is it not?

9

Simply discard the reading? Sorry?

(void) analogRead (myPin);
myReading = analogRead (myPin);
10

jtw11:
What I meant, was to be able to simultaneously read the input from an LM35, whilst reading other 0 - 5v sensors - in addition to running numerous other I/Os. A delay of any sort is a delay is it not?

You can't simultaneously read more than one analog input anyway. There is only one ADC. The pins go into a MUX, which sits in front of the lone ADC.