Solar Shed - Assembled

It is mostly assembled now.  First step is test the ADC inputs and make sure they are working correctly.  I built this spreadsheet.  

• Column A is Vcc=3.29VDC and ADC size is 1024 counts
• Column B is Battery input voltage
• Column C is Battery voltage at the ADC input
• Column D is the ADC counts for that voltage
• Column E is LT1085 voltage at the ADC input (input voltage is from column B)
• Column F is the ADC counts for that voltage
• Column H is Solar Panel input voltage
• Column I is Solar Panel voltage at the ADC input
• Column J is the ADC counts for that voltage

Finally the three numbers in row 2 (0.2015, 0.2035 and 0.1286) are actual measured voltage ratios of the voltage input and what is present at the ADC input for each input. Even though I used 1% resistors, there is still +/-1% over the marked resistor values.  And to be fully transparent, even though there are unity gain low bandwidth (10KHz) OP-AMPs driving the PIC ADC, the layout probably could have been better.  It is as tight as SMT0805 resistors/capacitors would allow and is surrounded by ground plane.  But not being an Analog Guru, it is probably just OK.  Below the table You can see the layout for the three ADC inputs. (It;s late and my hand is not quite steady, s the picture is a little fuzzy)

 

Then I compared these numbers against what the ADC was reading.  Finally I tweaked the Vcc number a few millivolts to get  a more consistent match of the table values to the actual ADC readings.  During this process I noticed that I had left the weak pullups on the three ADC input pins on.  After turning them off, the readings were much more consistent.

The next issue was going in and out of sleep.  Just needed to make sure that everything I turned on/off before sleep, was turned off/on after coming out of sleep.  So at least on the desk it seems to work as before.  There are a few enhancements and more testing that are needed

• When the solar voltage is high enough, run the PIC from the solar panel.
• Install the super cap and test it.
• Maybe the PIC runs from the solar panel all the time and the battery only powers the LED lighting in the shed.

Ran the system in sleep all night.  Starting battery voltage at 10PM was 13.68VDC.  At 8AM the next morning the voltage was 13.51VDC.  Now in LiFePO battery system this doesnt mean much.  Unless you have a calibrated battery gas gauge IC connected, there is no way to know how much battery life was consumed.   We must remember that a LiFePO battery discharge curve is quite flat until the inflection point.  What is important is the current numbers from the previous post, the system with OLED and in SLEEP, consumed 2.25mA from the battery.  That should be equivalent to 18mA-Hr.  Fully charged (and new) the battery is rated at 9.6A-Hr.  So over night we used about 0.2% of the battery.  

I will be interested to see what the super cap does.  That will be the next test.  Still waiting for the sun to appear and the snow to melt.