NiCD - Charging circuit - Using PIC

[Megahertz]

Thanks for the input guys. Prstein, you have surely got me thinking about using ADC. I have spent 2 hours today understanding it from the datasheet. It seems to me that I have an idea of what goes on (just kidding ), but still few clarifications needed.
1) I read 16F676 datasheet, it says 10 bit result - which means 1024 steps conversation. Now 1024 steps with what respect (is it the VDD)?
2) How do these steps relate to voltage supplied by two 1% precision voltage divider resistors on the ADC PIN.
3) In a nutshell, how does these 3 relate( internal VDD as Vref, 1024 steps, Voltage on ADC PIC by V. divider)?

After understanding the basics above, I will be surely be able to dig my way up and carry on with my charging solution. Having the knowledge from this thread only, I am considering using 12V Sealed lead acid battery and replacing NiCD. It seems if I can control the voltage drop of lead acid, it is more forgiving in terms of charging and it is cheaper as well + I only need one with sufficient current upto 4AH etc. Also using 12V in my TX is giving me increased range
Where as, putting two 4.8 NiCD in parallel, I have read that the current needs to be pushed in, and because the two battery packs may have different impedance(whatever that is), there is always a possibility of one charging more than the other.

So voltage drop of the 12V battery is sorted, can be done with comparator easily. Once ADC conversion is clear and the relation between 3 values mentioned above, I think I can do the charging & full charge indication as well.

[prstein]

Hi Megahertz,

The invincible Darrel Taylor has spelled it all out for us!

http://www.picbasic.co.uk/forum/content.php?r=245

Best Regards,
Paul

[Megahertz]

Darell is as always THE GURU of all this stuff. The example speaks for itself, no more questions on that front.

But if I have understood it correctly, he is measuring the voltage through a voltage divider, what can I do for current sensing? I think for that I need to add a very small value resistance in series to the current path and measure voltage drop across it, when it is nearly 0, battery charge is full, but what next? How to make a connection with PIC?

OR

Is that in his circuit he is actually doing the same thing? one set of divider on one side of the series resistor, and the other set is on the other side of the series resistor. Keep measuring both sides until they are giving nearly same readings?

[prstein]

I know almost nothing about current sensing. What little I do know I got from the MAX712/713 datasheet. I need to let others respond to this one.

Best Regards,
Paul

[pedja089]

You can use 0.1R resistor, in serial with batery. And measure voltage drop on it. I=U/R
Because you use smal value resistor( to reduce dissipation) you need to amplify resistor voltage. You can use just simple Non-Inverting Amplifier. Or something like MAX4080. Look datasheet for details. I used it, and it very simple, and it give 0-5V output, wich is perfect to use with ADC.