MC9S12NE64 ATD voltage scaling

cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

MC9S12NE64 ATD voltage scaling

2,454 Views
Ed22
Contributor I
Hi all,

I'm trying to use the MC9S12NE64 to monitor some batteries' voltages. The thing is, the voltage that I need to measure are either 24 or 48 V. I will monitor the batteries and set some kind of alarm when they reach a determined low voltage. I know that the ATD  input pins have a maximum voltage rating of 3.3 V on this microcontroller. So my problem is that I need to scale the batteries' voltage from the 0 - 24 V (or could also be a range from low voltage to 24V) range to the 0 to 3.3 V range, so I can use the on-board ATD to determine their voltages and don't overload the microcontroller. Can someone point me in the right direction as to what I will need to accomplish this? I'm kinda lost on this. Any help is really appreciated.:smileywink:
Labels (1)
0 Kudos
6 Replies

481 Views
nikosxan
Contributor I
Hi
 
Just as Lundin  said, 2 resistors should do. I'd say 10 K and 1K, with 10 K connected to battery and 1K to GND. This forms a 1/10 voltage divider and should get yous voltage down to 0-2.4V...
 
Also as Lundin sujested a 3.3 zener is good for protection of ATD input...I think could be replaced with a simple diode clump to VDD (+ power)
0 Kudos

481 Views
Lundin
Senior Contributor IV
Two resistors and a 3,3V zener diode?
0 Kudos

481 Views
Ed22
Contributor I
Thanks for the help! One last question: do you suggest connecting the Zener between VDD and GND?
0 Kudos

481 Views
nikosxan
Contributor I
Zener should be connected between the Inputs ATD pin and GND in order to protect the input from voltage > 3.3 V, since you have batteries of 24 of 48 volts.......Normally the voltage to ATD input  should be below < 3.3 V but in any malfunction you don;t want to burn the input............
0 Kudos

481 Views
Ed22
Contributor I
Thanks for all the help! :smileyvery-happy:
0 Kudos

481 Views
nikosxan
Contributor I
Sorry, forgot the 48 V part...In that case, change 10 K to 20 K, so resulted input to ATD should be 1/20 of input..........
0 Kudos