Voltage monitor for car battery

[malc-c]

The OA didn't say use the regulator for the sensed voltage, but for the supply voltage.

Sorry, mis-read the post

I have no idea where you get 58k and 41k resistors; these aren't standard RETMA values.

Whislt not standard a quick google will show that they do exist, or simple enough to make up the value.

[BobP]

Hi,

Don't forget to suppress the voltage spikes! A cars electrical system can generate spikes easily above 50v. Try to take the measurement points as close to the battery as possible. Also damp the takeoff point from the resistor divider with a small capacitor (10uF). I would also use some inductors in the supply line to protect the regulator and PIC.

Bob

[passion1]

Hi,

Don't forget to suppress the voltage spikes! A cars electrical system can generate spikes easily above 50v. Try to take the measurement points as close to the battery as possible. Also damp the takeoff point from the resistor divider with a small capacitor (10uF). I would also use some inductors in the supply line to protect the regulator and PIC.

Bob

Bob

Thanks for the advice! Could you be specific with regard to where the capacitor must be placed as well as the inductors. If possible, inductance values would be appreciated. (I'm rather new to electronics!)

THANKS!

[chuck]

Passion1

here is web link with values and op-amp

http://www.winpicprog.co.uk/pic_tuto...ogue_board.htm

Has for the zener diode you just put the block end to say PORTA.0 and the ohter to ground.

hope this helps,

chuck

[BobP]

Hi,

As per your request please find attached a quick and basic suggestion for values I would use.
As you have 10k resistors I used these.

Bob

[passion1]

Bob , Chuck and other

Thank you all for the advice. I really appreciate it!

[Melanie]

> Has for the zener diode you just put the block end to say PORTA.0 and the ohter to ground.

No!

A Zener starts to draw current long before it gets to it's stated voltage... it doesn't just suddenly 'turn-on' at it's rated voltage. As soon as the Zener starts to draw current (a 5V6 Zener might start as low as 3v!!!) then it will throw your Resistor Voltage Divider out and you will no longer have the ratio voltage drop you expect!!!

A Zener is good for protecting Digital ON/OFF inputs but not for precise measurement ADC or Comparator inputs.