Voltage monitor for car battery

[Pic_User]

You don't need me to defend you Adam *smiles* just asbestos underpants...
... then you've got a potential flame-out in a vehicle... mounted next to the flexible plastic piece of gasoline hose they've just fitted whilst parked at the filling station...

Geee... I think I missed my calling - should be writing disaster movie scripts in Hollywood...

> flame-out in a vehicle... mounted next to the flexible plastic piece of gasoline hose!

Now THAT is a second good reason to keep wearing asbestos underpants!
Does asbestos protect one from whip lashes?
-Adam-

[mackrackit]

Impedance of a DC voltage divider.

If I remember right

R or (Z) = (R1*R2) / (R1+R2)

Using the 3 to 1 example with 10K resistors - Z = 6.6K
Using the 4 to 1 example with 10K resistors - Z = 7.5K

No problem here, Besides that, I use the 3 to 1 example, It does work.

Asbestos <> RoHS Compliance

[Andy Wood]

Impedance of a DC voltage divider.

If I remember right

R or (Z) = (R1*R2) / (R1+R2)

Using the 3 to 1 example with 10K resistors - Z = 6.6K
Using the 4 to 1 example with 10K resistors - Z = 7.5K

No problem here, Besides that, I use the 3 to 1 example, It does work.

Asbestos <> RoHS Compliance

The OP hasn't specified a device. If using the popular 16F88, the maximum recommended analog source impedance is only 2.5k. It is always best to stay within the specifications of the device for reliable results.

Regards,

Andy

[mackrackit]

The OP hasn't specified a device. If using the popular 16F88, the maximum recommended analog source impedance is only 2.5k. It is always best to stay within the specifications of the device for reliable results.

Regards,

Andy

Are you sure you have the correct data sheet. Section 12.1, paragraph one in the data sheet titled PIC16F87/88 clearly states "The maximum recommended impedance for analog sources is 10K."

I do agree one needs to stay within the specifications if you do not want to see the magic smoke

[Andy Wood]

Are you sure you have the correct data sheet. Section 12.1, paragraph one in the data sheet titled PIC16F87/88 clearly states "The maximum recommended impedance for analog sources is 10K."

I do agree one needs to stay within the specifications if you do not want to see the magic smoke

Now there's a trap - the current datasheet from Microchip states 10k:

http://ww1.microchip.com/downloads/e...Doc/30487c.pdf


However, the (older) datasheet on the melabs site states 2.5k:

http://melabs.picbasic.com/devicedata/30487a.pdf


A good lesson - always ensure you have the latest datasheet!!!

Regards,

Andy

[mackrackit]

And to make sure you are not using old parts. MicroChip seems to make improvements every so often. With all of their products it is hard to keep up.

But I have to wonder, impedance being an AC term, does this apply more to an ADC source that is switching? Like an old load cell driver?

But as far as the original question on this thread, I think it has been answered and designed. Thanks to Adam.

[Pic_User]

Thanks goes to the Circuit Design Committee for the input and to passion1 for asking the all important question.
Great job nailing down the 2.5k 10k discrepancy, I replaced my old PIC16F88 sheet with the newer one.
-Adam-