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Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 03:22pm 11 Jun 2016

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So after contemplating & reading about using an external VRef, I notice on the Backpacks I'm using that Pins 2 & 3 are already in use for the LCD touch screen.

Might for now change my thinking on the solar panel output.

Was working towards 1000mV loaded = 1000Watts/m�.

Maximum unloaded output from the solar panel is about 2.9V.
Might try & change the loading resistor to try & get around 2.8 volts when the suns at it's brightest or around 1000W/m�.

Then just scale it from there for the time being.

Phil.

centrex

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Joined: 13/11/2011
Location: Australia
Posts: 320

Posted: 04:51pm 11 Jun 2016

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Hi Phil
I dont know what other pins you are using but pins 4,5,26,24 are all analog and free on the backpac.
Perhaps these could be used for your requirements.

Perhaps not Matherp appears to have pins 2 and 3 locked in to the cfunction.
Edited by centrex 2016-06-13

Cliff

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 05:55pm 11 Jun 2016

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centrex said Hi Phil
I dont know what other pins you are using but pins 4,5,26,24 are all analog and free on the backpac.
Perhaps these could be used for your requirements.

Perhaps not Matherp appears to have pins 2 and 3 locked in to the cfunction.

Pin 2 is VRef+ & Pin 3 is Vref- on the PIC, I didn't think other normal AIN pins could be used.

Maybe they can, but I don't really know, I just assumed not.

I thought the voltage to be measured could be any AIN, but the reference needed Pin 2 as it's the ACD's VRef+.

Cheers.

matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10209

Posted: 01:47am 12 Jun 2016

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Quote Pin 2 is VRef+ & Pin 3 is Vref- on the PIC, I didn't think other normal AIN pins could be used.

Correct I'm afraid - these pins are hardwired in the silicon

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 12:59pm 12 Jun 2016

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So my alternative could be LM336 connected to say pin 4, Voltage to be measured connected to pin 5.

Assuming Pin 4 returned say 3.5 volts, instead of the 3.25,
And Pin 5 was returning say 2.65,

Corrected voltage would be; 2.46 = 3.25(Ref)/3.5*2.65

Is that going to give me at least better consistency & accuracy?

Thanks.

TassyJim

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Joined: 07/08/2011
Location: Australia
Posts: 6269

Posted: 01:33pm 12 Jun 2016

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trueRef = 2.5 ' might want to get a precise value.

myRef = pin(4) ' LM336
myCorrection = trueRef/myRef

myreading = pin(5)*myCorrection ' do this for all analog inputs

you can also monitor the 3.3V using a voltage divider.

Jim

Eit.
The 3.3 can be determined directly from the reference reading without any other pin getting used. You can monitor other voltages such as the 5V or battery voltage by using voltage dividers.
Edited by TassyJim 2016-06-14

VK7JH
MMedit

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 08:37pm 12 Jun 2016

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Voltages I'm reading still seem all over the shop....

Reading pin 4 I think, with a bit of averaging.
Each reading only having a 10% weighting on the previous average....

Volts=volts*100

For n=1 to 10
Volts=Volts+Pin(4)
Next n

Volts=Volts/110

Still looks pretty ordinary...
A few random reading I've observed...

MM Volts Actual Volts
520 800
540 750
1060 1350
1300 1500

Have the panel feeding into the MM, with 27 Ohms Shunt, 0.1�F Ceramic across the shunt; Probably way too low???

3.3V rail on the micro seems rock solid on 3.31V.

Any Suggestions for a better result?

Thanks

Phil.

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