ADCIN car battery monitoring

[amgen]

voltage divider,
if you consider full-scale voltage to be 25.6 , a 10 to 1 resister ratio, then,
A) the voltage reading is directly from 8-bit acd value...... 125 would be 12.5 volts
B) and the applied voltage to PIC is about 2.5 volts

don

[mitchf14]

Thanks again guys, why would i need to put a reverse diode between the in and out of my reg, every time i add a diode i lose 0.7 v is it really needed also, what is the purpose of that 5.1 volt zener in their on my opinion that no good my reg needs minimum 6.5v to work.

Can someone please clarify this for me.

thanks

[Acetronics2]

Hi, Mitch

see 7805 Datasheet for that : it's for avoiding reverse current flowing through the regulator when input voltage is < output voltage ( typically @ power shutdown ...)

Note Anode is @ reg output and Cathode @ reg input .... !!!

Alain

[Andy Wood]

Thanks again guys, why would i need to put a reverse diode between the in and out of my reg, every time i add a diode i lose 0.7 v is it really needed also, what is the purpose of that 5.1 volt zener in their on my opinion that no good my reg needs minimum 6.5v to work.

Can someone please clarify this for me.

thanks

The value of the zener diode is incorrect. For a 12 volt system, a value of 18volts would be more appropriate. I would use a Transorb, not a zener for this task.

A 12volt automotive system can contain many voltage spikes much higher than the 12 volt battery. The transorb is there to protect the input of the regulator from these spikes.

If there is a possibility of the input being connected to a 24volt system, I would use a 33v transorb. Also ensure the capacitors on the input of the regulator have a voltage rating of at least 35volts.

The 10ohm resistor could be replaced with a resettable polyfuse. This way, if the transorb conducts due to overvoltage, the polyfuse will trip and go open circuit. When it cools down again, operation will resume as normal.

Andy