My boards came in and at least the model 100 one works fine.
There's room, but no good way to solder the qwiic connector to the
REXCPM, so the most practical way to handle the REXCPM side is just use
the pre-made adapter cable that has female dupont sockets, and stick
them right onto the original pins.
For the GND wire, you can treat it as optional and leave that wire
unconnected, or add a single solid-core wire to the big cap for the gnd
connection. If you use 23 gauge solid core wire, or maybe a size or so
thicker, the wire is stiff enough to hold it's shape and thick enough
for a female dupont socket to stick onto it and not fall off. I used 23
gauge wire from some solid core ethernet cable and that was about
perfect. Other common sources, thermostat wire, doorbell wire.
Take a 25mm piece of wire, strip 3mm on one end and bend it sharp 90
degrees, strip 6mm on the other end, poke the wire in between the cap
and the 3 pins and solder the short bent end to the cap.
Then the 4 female dupont wires go like this:
black (GND) -> wire on cap
red (/WR) -> closest pin to cap
blue (RAM) -> middle pin
yellow (RAM_RST) -> furthest pin from cap
It turns out you have to be very careful not to strain the original pins
on the REXCPM.. They rotate pretty easily and break the via free inside
the pcb, and then the traces break.
At one point I was stuffing the gnd wire down from the top in between
the pin and the cap, and that put sideways strain on the pin.
My REXCPM doesn't work now unless I hold the pins a certain way to cause
them to make contact.
I have to desolder a few parts to figure out where two of the traces go
so I can find where to run bodge wires. Fixing the original traces right
where they broke at the base of the pins is probably too fragile now
that the vias are moving like that.
Maybe I'll just remove the pins, fix the existing traces where they
broke, and solder flexible wires instead of pins where the pins used to
go, and secure the solder joints with glue or epoxy. Hopefully the
combination of the glue and the flexible wire, and being super careful
from now on, will be enough to keep the traces from breaking again.
So I think the battery board is fine, and the cable connection at least
for model 100 is practical enough (I'd prefer a matching polarized
connector instead of 4 individual wires, but there is just no good way
to add that tiny connector that won't be too delicate and just break in
no time) but my rexcpm is out of commission and I can't do any further
real testing to get real current and voltages etc right now.
I did have it fully hooked up and running briefly before I twisted the pins.
I can't test the 102/200 board right now, and the pre-made qwiic-dupont
cable is only 150mm, not long enough to reach all the way from the board
to the rexcpm. You could add short male-female dupont
extensions/jumpers, but that's kind of annoying.
For the 102/200 board, really maybe for both boards, maybe it's better
to just go down to 2 or 3 cells and full size generic 4-pin headers
instead of the qwiic connectors.
It does work fine for the 100 version though since there is a pre-made
cable that is long enough all in one piece.
I've updated the github with bom and pcbway links, and gerber zip for
the model 100 version.
I say it's safe to order the 100 version at least.
The 102/200 version I haven't worked out how best to connect to the
REXCPM yet.
https://github.com/bkw777/REXCPM_UPS
--
bkw
On 9/17/23 20:33, Ken St. Cyr wrote:
Thanks for the detailed explanation - I totally get it now. I'll wait
until you verify the board and post the gerber before ordering a set. I
typically have an order or two open with JLCPCB at any given time - for
just about every order, it's exactly 10 days from the time I click the
purchase button before the blue box shows up in my mailbox, and that's
with the cheapest shipping option. I'm not in a hurry to try it out, but
if I was, I would probably just mill a prototype board on my CNC.
Regarding the 4-wire connector... I'm happy to just solder the ground
wire directly to the REXCPM, though I'm sure most normal people would
prefer to have it on a connector.
//Ken S.
------------------------------------------------------------------------
*From:* M100 <[email protected]> on behalf of Brian K.
White <[email protected]>
*Sent:* Thursday, September 14, 2023 10:16 PM
*To:* [email protected] <[email protected]>
*Subject:* Re: [M100] rexcpm battery
On 9/14/23 21:27, Brian K. White wrote:
But somehow there is power differential between gnd and vmem (or
whatever the positive side of the big cap is, I say vmem because
obviously it powers the sram) on the rexcpm, and 0.7uA of current
flowing along RAM_RST.
7uA not 0.7uA!
--
bkw
--
bkw
