Being shy about hacking into my Nikon MH-33 charger for the EN-EL18d batteries, and not feeling shy about hacking the Wasabi charger that came in a set with two of it's batteries, I got this ball rolling.
I tacked thin wires onto the very tiny surface mount charge status LEDs and brought them out of the case and over to analog inputs on an Arduino Uno. The circuit points I tapped are downstream of the limiting resistors, therefore a bit "distanced" from the Wasabi's charge controller chip providing a tiny bit of ESD safety. The voltage states are 0.0V and 2.0V for Off and On states respectively.
[If I had instead fed the wires over to digital inputs on the Arduino even the On condition falls below the digital logic transition of 2.5V; it would always be misinterpreted as "Off".]
The "is it on or off" assessment threshold of the analog signal is set at 1.0V.
The set of three LED state signals are sensed at 250 msec intervals. I keep that up for 8 readings, therefore two cycles of the flash pattern. The flashing pattern is a 50% duty cycle 1 Hz square wave just like the Nikon MH-33. After I parse the results into Highs and Lows I can tell if the LED is solidly Off, pulsing, or solidly On.
The pattern therefore reveals the charge level at the same coarse level that we're used to on the MH-33.
When the "80" LED is solidly lit I pull the plug on the charger power.
Here's a sample of the running steam of debugging text coming out of the Arduino's serial port:
As soon as the Interpretation reaches the >=80% threshold, the power to the Wasabi charger will be cut out.
Obviously this is not a very travel friendly system, physically.
But a robust refinement is possible. It turns out that there is enough room inside the Wasabi case to accept a small custom PC board. An Arduino Pro Micro and a few MOSFet switches could run the show from
entirely inside the Wasabi case! When the charge level reaches 80% the MOSFets could interrupt the battery charge line and the communication lines. Thank you, Wasabi, for exposing those runs in the form of wire leads.
Left to right: Old school linear power supply fed by AC mains; charge controller board; dismounted battery connector daughterboard
The solder bumps on the surface mount LEDs are less than 1mm across, so use a tiny soldering iron tip.
[ATTACH alt="I'm shining that flashlight into an empty space with about 2" x 3" x 1" free clearance"]3307613[/ATTACH]
I'm shining that flashlight into an empty space with about 2" x 3" x 1" free clearance
The source code should transport with few modifications required. The missing elements at this point are a PCB which I would design in Eagle CAD, and a prototyping of the data interruption line. I'm presuming that a P-channel power MOSFet would be OK on the battery + lead. Failing either of those, then I could use relays.
The battery I'm charging right now will hit the 80% point in an hour or two. I'll report back with the Z9's power level readings of the four batteries I have. I hope to see a small spread.
--
Wag more; bark less.
