(ALWAYS REMEMBER: on the mini-board's J2, red/+/VBAT is the pin on the outside edge of the board. black/GND is the pin closer to the middle of the board. arduino has +/- written next to its battery jumper, not to mention a nice big arrow to the + pin )
nothing brilliant going on here, the idea was to:
- be lazy and not bother with any soldering, but also have durable+reliable connections.
- be able to swap batteries without ever needing to unplug any wires from Edison board itself. (also, once you have the harness on the Edison, never again worry about reverse-polarity-frying anything!)
- be able to add/remove a volt-meter if desired (esp. since as others have mentioned there is nothing in the charge circuit to get battery/discharge info via software)
- the battery I'm using only has a 25mm(!) JST lead on it (which actually may be perfect for some projects, but is way too short for me)
- can make each different leg of the harness whatever length you want.
- telco-style crimping tool e.g. Klein D234-6.
(but Klein are not inexpensive; you can easily find other cheaper brands.)
you can also simply use pliers, but you have to be quite careful or you will crush the connector. (the nice thing about the telco-style tools is that it's not possible to crush the telco splice-connectors)
- 1 pair gelpack triple-connectors e.g. 3m/Klein/Scotchlok VDV826-605
(knock-off brands are WAY cheaper, but I can't speak to quality/durability. anything equivalent of "IDC UR, 3-Wire, Red, 26-19AWG")
- 1 pair gelpack double-connectors e.g. 3m/Klein/Scotchlok VDV826-604
(ditto. anything equivalent of "IDC UY, 2-Wire, Yellow, 26-22AWG")
- a 1s LED voltmeter (i.e. 1-cell compatible - be wary, it's common to see ones that look similar but are 2s-6s)
I've been happy with:
-- NEEWER 1S-6S
-- SMAKN 1S-6S
-- Integy C23212
you can find many alternatives if you look in R/C car/helicopter/plane type categories/stores.
no idea of the voltage draw by the meter, but it's quite a small circuit board; and the nice thing with this harness is you can unplug it whenever you want.
- a 1-cell 3.7V battery, obviously. not many have IDC connectors, but any one with JST is close enough. be careful, a lot of the R/C batteries have tiny/weird connectors that aren't even close to fitting IDC-width jumpers, nor IDC-size pins.
-- the small square batteries from e.g. Sparkfun are something around 300-400mah, but you can find 1200 quite inexpensively, e.g. spamazon.
- some plug-end and socket-end JST 2-wire pigtails.
-- you can also use 2pin IDC stuff, but for some reason it's 20x the price. plus? JST is keyed, so it's not possible to mess up polarity later on! (as long as the actual connection to Edison was done correctly.)
-- note: even buying these in 22AWG, some of these have extra-heavy silicone insulation, instead of plastic; and can be tricky to get into the crimp connectors. getting some of the gel that's inside the connectors, can help coaxing stubborn wires.
-- pretty sure some of the wires I used were stranded, while I think the splice/crimps are ONLY supposed to be used on solid. but it's been fine so far.
the rest is embarrassingly-simple...
1. use 2 triple-connectors to wire 1 JST plug to 2 JST sockets (being careful to match wire color, obviously: red-red-red and black-black-black.)
2. the meter side of the harness, I made a bit overcomplicated, it goes:
- JST socket (from step 1) to JST-plug-doubleconnectorsplice-to-JST-plug.
- you could simply go from the 3-connector to a JST plug and eliminate all the extra parts.
I only did it that way in case I had an actual need for a socket later on
and also some sense of symmetry/flow, i.e. always trying to keep plugs in one direction and sockets in the other direction. (obvs this idea fails on the wire from meter to socket, ha ha)
3. the battery side of the harness, well it's a JST socket (already done in step 1) - simply plug in the battery.
even not connected to Edison, the meter continuously flashes voltage.
connected to the Edison, you get to see if the battery is charging or discharging.
I'm not sure how well-calibrated the meters are, although each of the 3 brands I tried are all fairly similar to each other. they do have some secret factory/calibration mode, but I wasn't concerned enough to try it.
battery seems to stick around 4.11, which seems ok. sometimes goes up to 4.20, which is a bit past-rating, but been ok so far, and the battery does not get warm (and behavior is no different whether with or without thermistor.)
couldn't get any decent photos, but if I do, I'll add them (although this is so simple it's not even necessary, really.)