Got the manufacturing test fixture designed, boards back and built.  Now to write code.  The test fixture will program code into the on-board micro (actually program two programs, the first used to find the micro's calibration value) and perform a functional verification of the electronics via pogo-pin connections with test points on the bottom of the PCB.  I am using a PJRC Teensy 3.5 as the test fixture controller.  The technician will interact with the controller to initiate programming and testing via a capacitive touch LCD screen (one thing I learned from Sparkfun's production line as a collaborator was that mechanical switches quickly wear out).  For boards that fail the programming and test procedure a small thermal printer will print out a diagnostic output to go along with the failing board for later repair.  I hope to be able to have the print out identify portions of the circuit to focus on.

You can see some power resistors that act as a load when switched onto various subsystem outputs by a N-Channel MOSFET.  If you look closely you can also see that I forgot to send them milling gerber layer to the PCB vendor for the non-round power connector contacts...

The test fixture, a power supply and printer will go on a base.  I'm not sure if I'll ask that the board be secured using screws or if I'll try to build something to press the board down onto the pogo pins.  In addition I also want to figure out an optical sensor to verify the on-board LED.  I bought some photo transistors that have sensitivity in the green range.  Just have to figure out how to have them see only the light from the LED and not ambient light.

Not just for Solar Power!

Have an old laptop power supply?  It can turn the charger into a long-lived UPS for small computers like Raspberry Pi file servers or a 5V router or WiFi access point.  I hooked an old Dell 19V 3.5A laptop supply to the solar input and the system worked flawlessly as a UPS.

The charger will initiate charging once the solar panel voltage exceeds 18VDC.  Many laptop supplies put out between 19 - 21 volts.  This is perfect as a source of power to both keep a battery charged and power a load through the 5VDC output (or even the direct battery connections although there won't be automatic low-battery shut down without extra circuitry).  The MPPT algorithm will find the power supply's set point and the charger will keep the battery charged without damaging with it's FLOAT charge state.  The battery will take over the load if the AC power fails and the existing auto-shutoff software support can ensure a controlled system shutdown if necessary if the battery is ever exhausted.  Depending on the load, this UPS can keep a load running for many hours or even days without AC power.  Even with a 10 watt 5V load (taking about 1 A from the battery/PSU) there will be at least an amp available for recharging the battery when power is restored.  The system will get warm under heavy load so some kind of cooling might be necessary, especially if it's in an enclosure.  Easiest would be to connect a 5VDC fan to the board so that it's also shut down for low battery cut-off.