How to detect low battery in battery powered F683 circuit

[tekart]

Mark, thank you for clarifying. I thought it was something like that but my inexperience with internal voltage references left me confused. I have ordered some F1822 chips to experiment with.

So would you mind clarifying for me how I would go about using the single pin to take advantage of the internal reference diode. Do I understand correctly that this diode would replace the external diode we have been discussing, so all I would need is a pull-up resistor on the ADC pin? I still don't see how that would give me a reading that would very since I would still just be reading the voltage drop of the reference diode. Forgive me for being dense about this but I still don't get it.

[mark_s]

Your battery positive will be connected thru a 1K resistor to the adc, you may need a divider if v battery is greater than VDD? Then you take a normal acin reading and determine what number between 0 - 1024
equals a low battery. If an < x then low_bat. else..

To start

Fixed voltage reference FVR page 137

ADCIN will take care of the ADCON0 register

FVRCON = %10000001 ' vref enabled 1.024v
ADCON1 = %11110011 'Right just,FRC,+vref connected to FVR

[tekart]

FVRCON = %10000001 ' vref enabled 1.024v
ADCON1 = %11110011 'Right just,FRC,+vref connected to FVR

Mark, thanks for the very helpful configuration settings. I got a test chip working fine using 8-bit reads and left justified results. I am in a similar position to peterdeco1 in that I have a circuit board designed for production and ready to go into volume assembly. Fortunately I already had two resistors connected to the A/D input creating a voltage divider so I am good to go - except for one minor problem. My test code works on the F683 chip just fine but when I try to implement it on my actual design I find that I do not have proper digital I/O on PortA.5 for some reason. My design uses portA.0 for the analog input and portA.2 for PWM out. I am struggling with what configuration error I have that is preventing portA.5 from operating as a digital output. I have been poring over the datasheet for an hour or so now and can't seem to find a configuration that seems to be setting that into something other than digital I/O. Any help would be appreciated.

[mark_s]

These "enhanced" pics don't use the GPIO like the old ones. Use porta.5 to read
and lata.5 to write. See page 13 and page 121 of the data sheet


Add: See Hecklers code and configs
http://www.picbasic.co.uk/forum/show...ght=pic12f1822

[tekart]

Wow. Thanks Mark - I missed that. I just HATE all these whiz bang "features" that force us mere mortal coders to spend *days* learning a new chip! Grrrr. <end rant>
SO to implement a pin as output only I use:
GreenLED var lata.1 ' high = light power LED
and also set:
' config
TRISa = %011001 ' set I/O directions (0 = output, 1 = input)
LATa = %011001

- still not getting it to work with above settings. Do I have bit polarity right for LATA?

[mark_s]

I think you would declare your variable as

GreenLED var PORTA.1

[tekart]

I think you would declare your variable as
GreenLED var PORTA.1

Been testing that and the compiler seems to accept either
GreenLED var PORTA.1
or
GreenLED var LATA.1

[gadelhas]

Hi;
The 12f1840 as Internal voltage reference ( Fixed Voltage Reference (FVR) with 1.024V, 2.048V and 4.096V output levels )

[tekart]

Thanks guys! Now I completely understand what I need to do and this solution will work extremely well for me. I have ordered some sample chips and will dig into this later in the week. I appreciate your help and patience.

[Dick Ivers]

Hi Tekart,
Do you have PBP3 ? I believe you will need it to use the 12F1822 or any xxF1xxx part.

[tekart]

Hi Tekart,
Do you have PBP3 ? I believe you will need it to use the 12F1822 or any xxF1xxx part.

Of course! Been using PIC Basic for over 14 years! Early adopter that came over from Basic Stamps. - thanks for checking though

[peterdeco1]

Maybe this will help. A while back we needed a low battery warning for a circuit that was already in production so it had to be done in reverse. The PIC was powered by a 6V battery with a diode to drop it to 5.4V. A jumper from an ADC pin was attached to a 3.3V regulator already on another section of the circuit board. Now as the battery voltage drops, the ADC result will rise, since the 255 reference will always be the battery voltage. The lower the battery voltage the higher the 3.3V ADC reading becomes.

[pedja089]

That is what I was suggested, just to to use diode instead of regulator...