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samus111
Joined: 28 Aug 2014
Posts: 29
Location: Colombia
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| PIC measuring voltage level from its own supply |
 Posted: Mon Jan 12, 2015 2:27 pm |
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Hi to everybody,
I have a project, and one of its projected features is the ability to measure its power supply level and send it by a email message. I never have used A/D converter with PICs, so, I am not sure if this can be possible. I have read a lot of posts, but all are focused in to read a external source. The problem that I see is that the Vref will change every time I try to measure the battery level. Is there some way to program a PIC with this feature or do you have a idea? Thanks. |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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samus111
Joined: 28 Aug 2014
Posts: 29
Location: Colombia
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| Posted: Mon Jan 12, 2015 3:32 pm |
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| newguy wrote: | http://www.ccsinfo.com/forum/viewtopic.php?t=24560&highlight=reference+supply
Measure a known voltage reference with your A/D. As battery (supply) level drops, A/D reading will rise. |
Thanks for your collaboration, basically the post you quote is for indicate a low battery alarm, well I will explain my project better:
The uC will control a transmitter, both components will be fed by 4,2V ( a single cell LiPo battery), The transmitter will work until the battery gets around 3,7V, and I need to measure constantly the power level. So, I want take the voltage value (not the low battery indicator). The Vref always will vary if I set it with the Vcc from the PIC, I wonder if maybe there is a internal zener diode that I could configure from the PIC or something alike, thanks. |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Mon Jan 12, 2015 3:49 pm |
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Hi,
You haven't told us which PIC you are using, so all we can offer are general comments/guidelines. Most PICs will allow you to specify the A/D reference source. By specifying an external source, such as a precision voltage reference, your A/D readings will be independent of the Vcc supply voltage. The external source is then applied to the appropriate PIC pin.
Search around the forum a bit, as this topic has been well covered in the past!!
John |
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samus111
Joined: 28 Aug 2014
Posts: 29
Location: Colombia
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| Posted: Mon Jan 12, 2015 3:56 pm |
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| ezflyr wrote: | Hi,
You haven't told us which PIC you are using, so all we can offer are general comments/guidelines. Most PICs will allow you to specify the A/D reference source. By specifying an external source, such as a precision voltage reference, your A/D readings will be independent of the Vcc supply voltage. The external source is then applied to the appropriate PIC pin.
Search around the forum a bit, as this topic has been well covered in the past!!
John |
sorry, I forgot, I am using the 12f1840, I have read the datasheet of it, but I don't find if a ability just like you have commented can be possible with this PIC's family. |
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gpsmikey
Joined: 16 Nov 2010
Posts: 588
Location: Kirkland, WA
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| Posted: Mon Jan 12, 2015 4:34 pm |
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If you are still in the design phase you might want to go back and look through the various PICs on Microchip - some of them have a built in precision reference that you can enable. A quick snoop turns up the 12(L)F1822 and 16(L)F1823 that appear to have internal references. I have not used those 2, but there are a possible solution. I know there are others as well (I have used the 18F14K22 and it has an internal vref as well you can enable although older version 4 of the compiler did not correctly handle it (I had to set the bits myself to enable it).
mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jan 12, 2015 5:22 pm |
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| Quote: | The problem that I see is that the Vref will change every time I try to
measure the battery level.
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12F1840 data sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/40001441E.pdf
| Quote: |
14.0 FIXED VOLTAGE REFERENCE
(FVR)
The Fixed Voltage Reference, or FVR, is a stable
voltage reference, independent of VDD, with 1.024V,
2.048V or 4.096V selectable output levels. The output
of the FVR can be configured to supply a reference
voltage to the following:
• ADC input channel
• ADC positive reference
• Comparator positive input
• Digital-to-Analog Converter (DAC)
• Capacitive Sensing (CPS) module |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Mon Jan 12, 2015 6:14 pm |
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| samus111 wrote: | | newguy wrote: | http://www.ccsinfo.com/forum/viewtopic.php?t=24560&highlight=reference+supply
Measure a known voltage reference with your A/D. As battery (supply) level drops, A/D reading will rise. |
Thanks for your collaboration, basically the post you quote is for indicate a low battery alarm, well I will explain my project better:
The uC will control a transmitter, both components will be fed by 4,2V ( a single cell LiPo battery), The transmitter will work until the battery gets around 3,7V, and I need to measure constantly the power level. So, I want take the voltage value (not the low battery indicator). The Vref always will vary if I set it with the Vcc from the PIC, I wonder if maybe there is a internal zener diode that I could configure from the PIC or something alike, thanks. |
Think about it - this approach will enable you to measure the supply voltage accurately. See what you can come up with and if you have trouble post what you have and we'll help. |
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