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Jul 07, 2019, 10:58 PM
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Standard LEDs with resistors are perfectly fine for this, if you're ok with 20mA or so load per piece. You may even parallel some of them R's to increase load, no need for additional LEDs or LEDs at all for the load, Mark used it as a cheap load of the "oh wait, i think i have some in my drawers" type.
I just looked at the github and the circuit says "power LED" and has no resistor for it, which is nothing you should use in reality, that's why i felt the urge to comment.

You did a nice combo of THT and SMT!
Didn't mean to question your knowledge or work.
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Jul 07, 2019, 11:14 PM
First joined Sep 2001
Thread OP
All good, you have been very helpful to me over the years, it is much appreciated.

Bm
Jul 10, 2019, 10:11 PM
First joined Sep 2001
Thread OP
Have tidied board up a little and removed power led.

I used 1% resistors for divider, have not calibrated unit and discharge terminates at 3.85V.

Question. I can't see accuracy is that important anyway, is there any reason why a single 85 could not be used to discharge several cells? Using other pins for each cell of course.
Jul 10, 2019, 10:47 PM
Registered User
That mainly depends on the circuit.
You need to keep the ADC voltage in the range, that means you're dividing the higher cells more, which lowers resolution.
And then the in- and outputs need to be ground referenced, so you're measuring not "cell 2" but "cell 1 + 2" and need to calculate the value for the cells, which lowers resolution more.
And find a way to discharge cell 2 without interfering with 1.
The low pin count is another challenge, 2S may be possible just with circuit tricks. 3S maybe, too.
Then you're out of legs on the 8 pin Tiny.

The main challenge will be the discharge circuit. Measuring is easy with dividers and maybe calibration of those.
But an almost currentless driven discharge load for higher voltages... I'd go for low side/high side (complementary) transistors. Should do for the low loads used here.
Jul 11, 2019, 02:10 AM
First joined Sep 2001
Thread OP
Thanks.

Bare in mind I am talking 1S, single cells. I have an Imax B6 for the bigger multi cell packs, and I know you can do multiple 1s on the B6 .

I meant to check schematic before last post, at best "pin wise" you "might" be able to do 2 x 1S cells. I don't write code, just enjoy building electronic projects.
Jul 11, 2019, 02:50 AM
First joined Sep 2001
Thread OP
There is the URUAV UR4 which would be fine for small cells.

Might even get one, but for now I am good.

https://www.banggood.com/URUAV-UR4-0...r_warehouse=CN
Jul 11, 2019, 03:31 PM
Registered User
Ah, ok, single cells are no problem.
Jul 15, 2019, 05:25 PM
Registered User
GeoffS's Avatar
Quote:
Originally Posted by BlRDMAN
... is there any reason why a single 85 could not be used to discharge several cells? Using other pins for each cell of course.
The only issue I could see is that you'll run out of pins pretty quickly. You need one analog input and one digital output per cell (to read the voltage and control the FET).

I've been playing with the attiny85 quite a bit recently. In most cases I ended up using a "Pro Mini" board instead. It's a full AtMega328 so it has more memory and pins. The board is only about twice the size of the Digispark attiny85.

With the Pro Mini you could control eight independent discharge circuits.

The Pro Mini is about $2.20/ea vs. $1.60/ea for the attiny85, so it's not really significantly more expensive.
Jul 15, 2019, 05:56 PM
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GeoffS's Avatar
BTW, since you are comfortable with SMD components, I'd suggest looking at at 5050 SMD led chip. They are typically rated at 3V and 60ma and can be had for about 3.5 cents each.
That's a bit less than the 100ma you were shooting for, but it would get the job done.

An SMD component would have the added advantage of having better thermal contact with the copper circuit board for heat dissipation.

At full charge of 4.2V you would need a 20ohm resistor to drop the 1.2V.
The resistor would dissipate about 72mW which is well under the rating for a 0805 (or larger) SMD package.

Another possibility is to completely dispense with the LEDs and just use two 100ohm 1210 resistors in parallel.
Jul 16, 2019, 01:48 AM
First joined Sep 2001
Thread OP
Thanks Geoff,

I am familiar with the Pro Mini, have a hand full of them and even made some projects with them. Problem is I don't write code, if someone else was to I would use it.

Out of curiosity what hardware do you use to program the ATtiny?

Bm
Jul 16, 2019, 11:27 AM
Registered User
GeoffS's Avatar
Quote:
Originally Posted by BlRDMAN
I am familiar with the Pro Mini, have a hand full of them and even made some projects with them. Problem is I don't write code, if someone else was to I would use it.
You should look at some of the Arduino programming tutorials. It's a pretty easy system to learn.
If you can design circuits, you should be able to pick it up pretty quickly.
Being able to write even simple sketches really opens up possibilities for new projects.

Quote:
Originally Posted by BlRDMAN
... Out of curiosity what hardware do you use to program the ATtiny?
All of my attiny85 boards have a USB connector on them (either "fingers" on the PCB, or a micro connector.
I mostly use the Arduino IDE (although I've use the Eclipse IDE's Arduino plug-in for some bigger projects).
Jul 17, 2019, 01:05 PM
Registered User
Quote:
Originally Posted by BlRDMAN
Thanks Geoff,

I am familiar with the Pro Mini, have a hand full of them and even made some projects with them. Problem is I don't write code, if someone else was to I would use it.

Out of curiosity what hardware do you use to program the ATtiny?

Bm
You can use an Arduino (any Arduino) to program an ATTiny, using the Arduino ISP programmer choice. More here https://create.arduino.cc/projecthub...ino-uno-afb829 (it uses an Arduino Uno, but even a Pro mini works, just connect the right pins)

There are other specialized programmers (e.g. USBAsp), but using an Arduino is just about the simplest way

As GeoffS says, there are specialized boards called AVR USB (aka USBTiny) that come preloaded with an Arduino bootloader and V-Bus (originally designed by Micronucleus, now cloned by pretty much everyone), but unless you have that specific board and are willing to give up part of the ATTiny memory for the bootloader, not as universal as a ATTiny85. Ironically you can use an USBTiny as an USBTiny ISP programmer to program a standalone ATTiny (basically the USBTiny is a version of an Arduino, and as such can be used as a ISP)
Jul 17, 2019, 07:32 PM
First joined Sep 2001
Thread OP
Thanks rob

I had trouble programming tiny with usbasp so I threw together my own diy uno, it has not let me down. I'm sure I used command prompt on my first tiny projects.


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