Reading 12 volt DC input via ADC

[TedO]

Hi guys,

I would appreciate some help understanding how to read a 12 volt battery level using the ADC inputs. I have experimented with the 5 volt ADC of the variable resistor pot and understand that, but am not sure how to approach the higher voltage input scenario?

Any suggestions would be appreciated.

Thanks
Ted

[Benj]

Hello Ted,

I would use a simple potential divider resistor circuit to drop the 12V down to something you can read directly.

12V
|
10K
|
|- ADC Pin
|
1K
|
GND

This would give you 1/11th of the voltage to the ADC pin.

VOUT = (12V / 11K) * 1K = 1.09V

Changing the resistor values will give you different voltages so the ideal is to take your maximum possible voltage (maybe 14V for a 12V battery) and choose resistor values to give you 5V to your ADC pin. This way you get 5V / 1024 discreet values = 4.88mV resolution.

[TedO]

Hi Benj

Thanks for your solution, will build up a resistor chain on my breadboard and play around with the values.

Regards
Ted

[Steve001]

HI Ted ,

if you look at martin's post on this thread he posted a 0 - 15 volt voltmeter

http://www.matrixtsl.com/mmforums/viewt ... 99&p=20326

Steve

[TedO]

Thank you Steve...much appreciated.

Rgds
Ted