In this size at least yes. I momentarily forgot that earlier when I was looking at circuits instead of the board, and with all the discussion of it. I might raise the idea in another thread.
Yep, and it makes it a simple place to test this RC idea. Once my hot air station gets sorted, I might just give it a go. I've got all the bits, enough for two to compare for that matter.
Yes, so I'm not sure this is settled. I went with 360k/47k because we had strong confirmation of 36k/4.7k working well for 4S clicky. That will give the same divider obviously, and there are no OTC issues, so I thought that should be fine. Most of the early adopters will have the 220k on hand if needed anyway, so worst case is we change it and learn. Anyway, we can certainly change the part list if we're sure. I'm still not.
So I’m probably missing it, but I just can’t see how that lower right quadrant could ever be ground. The upper right is + and the upper left is - and in 4s all other battery contacts are not ground. (the ground of a battery maybe, but not the ground, any raised voltage will due for the uv pin). I’m assuming there will be a jumper connecting the bottom two pads then.
For 2 S one of each of the bottom right and bottom left must be plus and minus. The mid voltage plane must be at the tail. There’s no other possible way. But I can’t imagine why the lower right would be ground. That would require connecting diagonal pads which is not simple to even do. The only thing that makes sense in 2S the lower right is connected to hot and lower left to ground, with vertical jumpers or traces on each side.
I’m wondering if you forgot to flip the board over in your head when you said that’s ground. If I’m confused, ok, but if I’m not, the jumper thing is real simple so maybe worth double checking.
I still think we should redo the voltage divider to whatever is ideal for the voltage in this case. Very few people have the components on hand for high voltage builds as it is so not a big deal to start over in this case.
Am I right that 4x the R2 should be roughly what we need to get the same reference voltage for the MCU with 4x the voltage?
So it would seem that an 47k/880k ish would be what we need?
Mostly because I do not know what reference existing firmware’s are using. It needs to be setup for whatever they are using now, which I think is the 1.1V reference.
Changing the reference is over the head of most people (including me) so it needs to work with whatever it is setup for now. Calibrating it is pretty simple by comparison.
Obviously other solutions will be needed for smaller boards, and I know you're always thinking about that. But with how silly simple this is.. I'd just worry about that later. It's solved here.
Never mind, that's not even right. In 2s tube lights there's only hot there.
But according to MTN max order site, they say to use 36/4.7 for 4s and DB confirmed, so it seems someone at least has software setup for 2.56. That's also what DB seems to have verified (he said 2.55, I think the programmer's approximation, but the spec sheet is actually 2.56)
Yeah, there is firmware to support it out there but this will be running on either Narsil or Bistro. TK is MIA lately so we have to use whatever it is setup for since no one else can really edit this type of thing.
Narsil I have no idea on but it would be best to not need a separate firmware just for a voltage divider.
In the case of Bistro it uses a 4.7k/19.1K and ends up around 50% of the usable range.
Running quick math that lines up with a 1.1V reference but a 2.56v reference would have the divider be something like 4.7k / 5k. This suggests that the 1.1V reference is used and as such should be what we aim to use as well to keep things standardized.
I am a major fan of standardization, it is the entire reason I made the TA drivers to start with.
Mtn max reccommends the same for 1S. Hmm... yes that comes to about 0.86V max, 0.833 for normal cells. I'm not sure why they changed it for 4S. Must have been a reason, but I definitely get your point. This is why I wanted to really verify what's being used around here as far as software.
If we want to hit 0.833 that's (16.8-0.833)/0.833 =19.2 which gives 90K R1
If we want to bump it up to 1.0V that's 74k, call it 75 to be standard. A 68K, a bit more standard, would make it 1.08, pushing it, and over the top for full 4.35 V cells.
82k, also a bit more standard gives 0.91V, seems pretty good to me. I could go with that.
Of course standards are fine, but what standards? 36 seems to be a somewhat standard 4S resistor value. 1.1 seems to be a somewhat standard internal reference. Software standards then? Ok, nobody is around to change it now, but we will need new software for this driver. We'll want dual PWM modes. I guess you've been playing with modes, so if that's something you can handle then great.
Anyway, 82k is fine with me if you've got a way to make it run.
But what about calibration. Do we have people responsive who can deal with that? If not, we better go with a 91K to keep even the calibration the same.
another issue, so it's not 90, it's more like 900. At such high resistances I get worried about stray current through places it shouldn't go. 10Mohm becomes an important path that level. So I read the manual and it says ADC inputs are subject to the input leakage current of the pin... which elsewhere in the manual is specced at 1uA. So that's 6% of our divider current. Ok That actually should be ok. But it will reduce the voltage by 6%. So much for using existing calibrations. Enh, it might be less than this since it's only 1V on the pin, not 3 or 5.
Still I'm a bit tempted to lower R2 to around 1K. 18uA of current makes me slightly nervous.
Recalibrating it is easy, anyone that can compile the software can do that. You simply flash TK’s calibration firmware and read off the numbers it spits out at a few voltages, feed those to the script she made and boom, you have your new calibration. Takes a little time but not hard to do and no coding expertise needed.
Far as firmware for this driver, it will run on the standard Narsil / Bistro firmware no problem. You will simply have to play with the PWM and modes a bit to dial in everything but once again, just a matter of playing with numbers, no actual coding going on.
Ok, I spent the morning re-working the driver for what is hopefully the final version.
I was able to increase C1 to a 1206, removed the jumper and generally compacted everything for as much edge clearance as possible. Still not a ton though, only about 3mm at the closest points but that is just enough to clear most of the SRK’s I have laying around.
If this looks good to go then I will put together a completed package along with a shopping cart link and people can give it a try at their own risk.
Nice work, a good looking board. I'm a bit surprised you left the Ruv's in. It won't hurt though. I guess you're worried we won't ever figure out R1? It defeats a good bit of the space saving though. I will try to dig through source and code and attiny manual code and if I can get to the bottom of the R1 thing.
Might reach 15A for some seconds. 0.6V dropout should be achievable at that current level in theory at least, for a perfect battery of course. The driver is capable of opening up to 100% duty cycle, basically direct drive, but with a bit more resistance from parts. It can take 16.8V input.
