Expanded Scale Voltmeter

[Pic_User]

Hi Alain,

I have a LM431A, in a solderless bread board, sitting on my workbench. I wanted to test the parameters at the span of interest. So far the stability of the 431 is impressive. It is configured as the standard shunt like the Zener in Figure B.
<IMG SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=2340&stc=1&d=120239628 9">
Reading the specs on the device is one thing, but seeing it perform; priceless.

You are correct about both points, Zener temperature stability and battery voltage being dependant upon temperature. Hmmmm, I will have to check the coefficients of each to see if physically tying the Zener to the battery might compensate for each other. lol

Now, it would be simpler to tell us what's you've in mind ...

Mostly just thinking "out loud", and wanted to throw this in for discussion. Lead acid is a good place to start. Later, maybe measure for the “signature” of an end of charge for Nickel-Metal Hydride (NiMH) or similar cells.
I can’t help with the programming, so this is my way of helping the discussion that is so great on the forum.

Melanie said it in the other thread:

Trouble is I can guarantee your 5v reference probably isn't 5.0000v (and are you using 0.1% Resistors?) so we're splitting hairs about millivolt ADC tollerances anyway.

This sounds right to me, so it looks like we have to be careful not to overrun REAL world limitations chasing down the wrong path!

The software, averaging and/or weeding out aberrations is a great idea. I like the “bomb proofing“ technique brought up by Melanie.

Thoughts:
So, after we stabilize the Voltage device, do we want to probe (measure) the battery temperature? Put the temp into a program for correction?

Any other thoughts on the matter?

-Adam-

[Acetronics2]

Hi Alain,

Thoughts:
So, after we stabilize the Voltage device, do we want to probe (measure) the battery temperature? Put the temp into a program for correction?

Any other thoughts on the matter?

-Adam-

Hi, Adam

On this point ... you're a bit late !!!

http://www.rc-cam.com/forum/index.ph...opic=2331&st=0

see posts 15 and 16 ...

for you, PbP source could be available !!!

But note voltage has not been corrected with drawn current ( in this use, quite constant ) ... another fun point to solve !!!

Alain

[Pic_User]

Hi Alain,

Looks like the temperature measurement while reading Voltage idea has already been put to use. By you!

I was not allowed to view the PDF you listed on the other forum.
After joining the forum was still unable to look at it.
I am interested in the pbp code and the PDF.

Are the batteries in those RC models high amps?

-Adam-

[Acetronics2]

Hi, Adam

The batteries in the models are supposed ( LOL !!! ) to be High Amp ... for the voltage not to "swing" too much when servos draw current.

That's why AA High cap. NiMh cells are NOT to use ( too high internal resistance )

You're right, we must register to download files at Mr CAM's ... some kind of courtesy !!!

For the files ... I think you got the scheme, I do not know why happend, but the Hex file is no more downloadable ( Forum doesnot bear .bas and .hex anymore !!! ) so, ... find the source here !!!

This program has been designed for low amp use ( Tx batt survey ), and the current is quite constant.

For Rx side ... things are much more complicated as current drawn can reach 2 or 3 amps for short periods, and the "quiescent" current is around 50 - 100 mA.

A not too false approach, is to move all plane control surfaces ON THE GROUND ... and see if buzzer ... buzzes ! ( current is then 1 - 1.5 Amp - so voltage has to be fixed for such current )
If it buzzes ... it means it's a good thing to charge batts ...


You'll find the Current / Voltage curves in the thread I gave you the address ... but those curves are for the Batts used in Txs ... ( 2000 - 2500 mAh LiPos )
You have to take YOUR BATT dedicated curve ...

Don't hesitate to Ask for any help ... the batt world is a Wild world !!!

Alain

[Pic_User]

Hi Alain,

I have been reading some of the stuff on the rc-cam.com forum. It is really interesting.
At first they wouldn’t allow the PDF down load, even though it congratulated me for joining. Then today, I tried and had no problem. Sooo, got the schematic and now got your code. Seems I can read PBP written in French, but the comments are a little fuzzy. Thanks for the files.

Reading the Voltage under high Amperage variations is a bit of a problem. My case let’s me stop the current and measure the Voltage. I will check the curves on the other forum and apply the principles to this project.

Probably good to check the batteries, on the GROUND, on a helicopter. We can imagine how well they fly without power!

The battery world IS a Wild world. The PIC world is a Fun world! I will be reading your information tonight. Thanks for the help.

-Adam-