That is why the adafruit has the control board breakout
needs a tiny circuit to run it…and firmware
I think you could bitbang i2c with an ATtiny. You could take the voltage reading using the standard divider method on the ATtiny and then output it to the display. You’d need additional space for the larger firmware - probably an ATtiny85 with Arduino would be the most straightforward way to build it.
Ok, first two sentences were automatically translated into [I think you could BADA-BING SOMETHING with a THINGY. You could take the voltage reading using the standard DOO-DAD method on the THING-A-MA-JIGGER and then output it to the display]. I understood the last sentence just fine. More doo-dads and thingys suggests that it won’t fit in a small light. 
Not at all! The Arduino environment works fine (ish) to write code for a bare ATtiny85, such as the ones we would use to replace an ATtiny13 in our flashlight drivers (they have a similar footprint). You simply write and compile your code to a hex file and then flash as we normally do. There wouldn’t be room for a lot of shenanigans (no stars), but I think there’s enough room for a momentary switch, voltage monitoring, and i2c. So the limiting factor is probably still the physical size of the display, although I did not look at what it needs for a power supply.
That sounds cool. Maybe a BEC like for radio control vehicles. They must be smaller by now. My last one was 22 years ago.
scottyhazzard I took a glance at the manual for that display. The tricky bit is that it wants two fairly different supply voltages. The good news is that it has an internal (boost) PSU for the higher voltage. The bad news is that the overlap between supply voltages is still very minimal, even taking advantage of that boost PSU. I think it’s possible that a simple 3.3v regulator such as the MIC5235 Microa mentions here could power the whole thing. It is a small component and requires one capacitor. The display itself requires 6 capacitors and 1 resistor when powered in this way. All in all I think it’s possible to add this stuff to a very small PCB or even onto an existing driver if there is a little bit of space. Any application that can accommodate a display of this size certainly has enough space. Even if running both VDDB and VDD off of 3.3v doesn’t cut it we could easily drive VDDB on one 3.5-4.0v MIC5235 and VDD on a nice comfortable 2.8v MIC4235. That’s still only 2 small components and 2 small capacitors. Bottom line is that there is no need for a bulky BEC (and the other bottom line is that needing 2 input voltages makes the BEC a less desirable route anyway).
EDIT: the display has a ribbon cable that requires soldering directly to a PCB. Rather than waste space why not just make that the PSU board and driver PCB as well?
Now for the host, what to put it in? Something that takes multiple cells I would think. M6, SRK or there’s that style that has 3 18650’s in parallel but one emitter…
Heh, no need to worry too much about that. If you build it they will come.
Unfortunately I doubt that anyone is jumping up and down to do the legwork required to actually get this working. I’m not. 
Sometimes it crosses my mind that a very small oled display could be neat. But then I remember its a flashlight. Bit excessive, no? Feels like you’d need to search for enough information to display in order to justify it. A tiny 7segment could be enough.
IIRC that’s what Rufusbduck has been advocating. (A 7-segment bar, ring, or similar - not a 7-segment numeric in case there was any confusion) We could easily drive one of those with a shift register attached to an ATtiny. They make shift registers who’s parallel outputs are already LED drivers.
At a glance maybe AS1109-BQFR or STP08DP05XTTR ?
Recall what thread he was talking about it in? Must have missed it.
7 segment like little LED dots? I always thought that the little blue battery status on my Apple laptop were classy and discrete… Maybe lined up in a circle around the switch?
Uuum apologies for awakening an old thread but I have a desire to for a small, inexpensive voltmeter, does any one know of any gems?
Usage, my camera does not like after market batteries and though it will work with them it gives no indication of the state of charge until they battery is in need of recharging.
It has occurred to me I could attach a small digital voltmeter to the battery grip attached to the camera, space is obvious limited.
I have ordered one via ebay
https://www.ebay.co.uk/itm/2-Wires-Mini-DC-2-5-30V-Voltmeter-LED-Panel-3-Digital-Display-Voltage-Meter-HDU/303095831026?ssPageName=STRK%3AMEBIDX%3AIT&var=602027118680&\_trksid=p2057872.m2749.l2649
whether or not it proves suitable is anyone’s guess.
Actually I would also like to add an on-off-on switch (tiny) as well, as the batteries (2) within the grip do not share a common connection and the camera ‘monitors’ both separately.
I would add a photo of the battery grip’s end but I don’t see how to upload a photo directly from my computer.
Thanks
These are small and good for lion but you don’t mention what battery type. These will only display anything from 2.5-3.0 volts and up depending on which color you choose. Otherwise, there is not enough volts to power the display. One good thing about them though is they can be calibrated using a multi meter and the screw (pot) on the bottom to be more precise. I actually have one of these (in red) on order so i can add to one of my battery chargers that only displays a less precise “gauge”
Thanks
Li-ion, nominal voltage 7.2V, recently charged and unused 8.2V.
Sorry, I missed the calibration pot in the advert photos, is it that what looks like a cross head in the centre of the underside? Does the accuracy of the voltmeter wander significantly over time?
Can the mounting tabs be cut off?
The one I ordered hasn’t arrived yet and I’d not be using a screw mounting in any case
If you can do this with an ATTiny85 and an oled…then I am sure a simple volt meter could be done
oh snap…check out the pico328
Uum, thanks but being honest I think that would be beyond my capabilities without a fair bit of studying. Though the size might be more suitable.
I use on my voltage sensitive Aux or tail boards a voltage comparator so I have 2 voltage levels like 3.6 and 3V to light up a different LED color
So 3.6-4.2V green
3.3-3.6V blue(yellow is pretty inefficient
3-3.3V red
Adding a 2.93V IC shuts it down below that, so no more parasitic drain of abou 0.05mA or more depending on LED brightness
I made a board to refit flashlights that has 14mm diameter with all components but this uses only 2 steps high, low warning and off, not implemented the complete shutdown so about 0.05mA remain below shut down
Oooooo got the voltmeter and it just about perfect for what I want, I am chuffed!
Now a daft question or at least it will probably seem so to you guys, is there a way to dim the display? It is very bright.
Sean, you can buy these voltmeters waaay cheaper, take a look at FastTech for example: 0.28" 3-Digit LED Voltmeter Module (3-Pack)
Use the right side drop down, many colours and assorted packs available.
I bought a 3-pack of greens long ago, they seem moddable for 3-wire common ground operation. The red wire connects to a pad nearby an unused one which is connected to it via a jumper (0 Ohm resistor). This means removing the jumper will allow the unused pad to work as signal line. Not tried it yet.
^:)