01 – boards v0.2 ordered for tests

A project log for Universal LiPo/Li-ion UVLO (undervoltage lockout)

Feature-packed over-discharge protection. Set the cell-count (2S to 7S), minimum cell voltage and dip-time below threshold. Fully hackable!

JanJan 04/27/2019 at 11:2010 Comments

Update May 15th, 2019

Just soldered the first V0.2 board on a hot steel plate:

It works, burned the bootloader (for fuses) and the blink sketch. Runs just fine. Next I'll try to read the three pots and switching the MOSFET on/off.

Edit: Everything seems to work so far. Will post an update soon to keep you posted!

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Update May 14th, 2019

PCBs arrived:

Hope I can test them this week!

Update May 13th, 2019

Got all of my parts, the PCBs will arrive this week as well. Hope to get the first prototype soldered before the weekend!

Update May 5th, 2019

v0.2 - sent to the fab on May 5th 2019

So, as I said earlier I didn't like my first v0.1 design. Digging through the schematic again before sending the board off to the fab I saw a few things that wouldn't quite work the way I though they would.

Here I'd like to thank @Simon Merrett for his support! He had a lot of good advice to give and helped me getting some things sorted! Sometimes some stranger asking "why this", "why that" is everything that's needed to question some of your decisions :)

The board now is:

Of course this still is not the final thing, but if it works as expected, getting it smaller will be no big deal.

We'll see. Boards are ordered, parts are on the way too...

Original post - just for reference

Okay, so this thing is not a beautiful piece of hardware. To be honest I don't like it myself, the layout is very shitty and much space is wasted. But I need a first revision to get myself started :)

Board revision 0.1 for first tests

This is not how the final board will look like, not at all.

Things that'll change:

  1. size-wise
    1. board must be smaller. I aim for 50x35 or 50x40mm
    2. limit height by removing those header pins and screw connector (need them for debugging and stuff)
  2. hardware-wise (going cheaper!)
    1. Atmega328P is overkill. Will work with an Attiny24A-SSU or something like that. Much cheaper, too at 0.65€
    2. looking for a substitute for those pots. Ideas?
    3. U4 is a MIC5018 boosted MOSFET driver to have a constant 10V drive voltage regardless of the input voltage which can be lower! At 1.1€ those are expensive. MIC5018 is half of that. Anyone know a similar chip?
    4. smaller caps will be used. 1uF @ 50V in 0603 are super cheap and much smaller than the 1206 I am using at the moment
  3. (…)


Simon Merrett wrote 05/13/2019 at 09:00 point

Re: Update May 13th 2019 - hooray!

  Are you sure? yes | no

Simon Merrett wrote 05/05/2019 at 15:29 point

@Jan , you're welcome! Now I see the mechanical design (rather than the electrical stuff we have been discussing), maybe some decent mounting holes at the XT60 end would be good - those connectors can take a bit of force to make/break. 

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Jan wrote 05/05/2019 at 16:18 point

Right! The last version had an XT60 90° connector with two support pins. Guess what I forget to include with my order at LCSC!

The final board will have that lying connector again, same for the output. Which will then be on the opposite side again as well.

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Jan wrote 05/01/2019 at 09:07 point

@Alan Green  Those dev-boards look like "better" Arduino Nanos! Too bad it needs AS7. The problem is not ME but I would love to make my board programmable/hackable by the community as well.
This unfortunately restricts me to the older range of Attinys and Atmegas. At least until UPDI-programming is more common.

Need to get me one of those dev boards though!

  Are you sure? yes | no

Simon Merrett wrote 05/01/2019 at 09:22 point

I think the appetite of the community will be bringing those new chips into service pretty quickly with cheap and OSS/OSH toolchains. For example, @Alan Green mentioned pyupdi and I have successfully pressed an Arduino Nano clone into service as a jtag2updi programmer to upload from avrdude and AS7 to ATtiny402. The serial programming elements of avrdude.conf can't be used so reading and flashing fuses from there isn't a straight forward thing but I would wager that people will soon have that door smashed down. PS, there are some signature HW bugs in some of these newer ATtinys, so be prepared if you try them barebones, rather than on a dev board!

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Alan Green wrote 04/28/2019 at 22:21 point

While you're looking at the Attiny24, you might also consider the 0-series and 1-series chips. The Attiny204 is roughly equivalent to the Attiny24 but about 2/3 the cost. The 404 is about the same price as the 204 and has double the RAM. 

Also, for the same price as the Attiny24, you could get an Attiny416 in a 24-VQFN package, which will give you 21 I/Os after accounting for power, ground and UPDI pins.

The downside of these new chips is that they aren't supported in an Arduino library yet.

  Are you sure? yes | no

Simon Merrett wrote 04/29/2019 at 07:11 point

@Alan Green I also think they'd be good options, depending on "pin creep"! Do you have any good resources for working with them? I have basic programming going with AS7 but would like to get fuses sorted with avrdude if possible 

  Are you sure? yes | no

Alan Green wrote 04/30/2019 at 21:04 point

I've been using the standard (I guess soon-to-be-legacy) commercial toolchain of AS7 + START + Atmel ICE. Between the generated libraries, datasheets and the odd peek at Arduino library source, I've had plenty to go with.

I'm currently curious about the new toolchain with MPLAB IDE and the $20 MPLAB Snap programmer. 

If you're wanting to go really cheap, you could look at for programming, but it lacks debugging capability.

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Jan wrote 04/29/2019 at 07:22 point

Hi Alan and thanks for your input!
Indeed, those Attinys look good. The 416 seems perfect for my needs. As all the functions are quite low level, I can program it bare-bones without Arduino "IDE".

The Attiny204 is even cheaper. I'll def. look into those!

  Are you sure? yes | no

Alan Green wrote 04/30/2019 at 21:09 point

Ooh. If you're looking at the 416, check out the $10 416-xnano dev board. If you're using Atmel Studio 7, it Just Works.

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