Arduino Programmable Constant Current Power Resistance Dummy Load

[wigman27]

Hi All!

I have built a programmable dummy load inspired by Daves initial one, I think it was episode 102? It is capable of constant current, resistance and power.

This is the link to the Instructable http://www.instructables.com/id/Arduino-Programmable-Constant-Current-Power-Resist/ I would really appreciate your feedback on the instructable and the theory within.

I have also done my first 3 three tutorial videos on using SPI that I am really happy with, videos are hard to do well, and Dave does it very well!







I just wanted to thank everyone on this forum that has helped me through this process, I have learned an incredible amount and pretty happy with my first real project, schematic and PCB!

Thanks again

Lee

[jackbrouno]

Nice tutorial

[miguelvp]

subscribed for a later view.
Only feedback I have so far is the sound quality, not a show stopper but something that could make a difference in the future, I only watch a bit of part 2 since I don't have time until later, so it might not affect the other videos

[rob77]

nice one ! i like it 

but probably i would go for better op-amp than lm324 in case of a 12bit DAC/ADC. for example OP07 is cheap and has a order of magnitude lower input offset than lm324 (75uV vs. 2mV).

[wigman27]

Only feedback I have so far is the sound quality, not a show stopper but something that could make a difference in the future, I only watch a bit of part 2 since I don't have time until later, so it might not affect the other videos

I agree totally! I am looking into a good mic to use, any suggestions?

but probably i would go for better op-amp than lm324 in case of a 12bit DAC/ADC. for example OP07 is cheap and has a order of magnitude lower input offset than lm324 (75uV vs. 2mV)

Again, I agree totally :-) when I started to fine tune everything, the offset voltage was my biggest limitation, however, some kind people on here helped me significantly with calculating the resistors and capacitors to deal with the phase shift. I haven't looked at the output resistance if that other op-amp but I wasn't capable of calculating it myself at the time. It's certainly something I will do better in my power supply :-)

Thanks again for the great feedback!

[ozwolf]

Hi All!

I have built a programmable dummy load inspired by Daves initial one, I think it was episode 102? It is capable of constant current, resistance and power.

This is the link to the Instructable http://www.instructables.com/id/Arduino-Programmable-Constant-Current-Power-Resist/ I would really appreciate your feedback on the instructable and the theory within.

I have also done my first 3 three tutorial videos on using SPI that I am really happy with, videos are hard to do well, and Dave does it very well!







I just wanted to thank everyone on this forum that has helped me through this process, I have learned an incredible amount and pretty happy with my first real project, schematic and PCB!

Thanks again

Lee

Subscribed and added to watchlist for tonight's viewing when SWMBO has gone to bed.

[TheAmmoniacal]

Can you set a cutoff voltage on this load? I'm interested in testing batteries and cell health, it would be helpful if the load didn't undercharge them.

[wigman27]

Can you set a cutoff voltage on this load? I'm interested in testing batteries and cell health, it would be helpful if the load didn't undercharge them.

Hey Mate

Currently the software doesn't allow it but it is certainly possible! It is able to sense the input voltage and you would be able to write a small piece of code to not let it go below a certain voltage without too much trouble at all. I might even add it to the next software review list

Thanks

Lee

[wigman27]

Hi,

I am thinking of running some more PCBs, would anyone be interested in buying one for $10?

Thanks

Lee

[snooky]

Hi Lee, Put me down for 2. I'm in Perth,

Thanks,
Greg

[con-f-use]

Didn't Dave have a go at your board in one of the recent mailbags?

[Sjokolade]

Yes, I will buy a board.

[wigman27]

Didn't Dave have a go at your board in one of the recent mailbags?

Have a look for yourself. Starts at 19:25 if the link doesn't do it automatically

http://youtu.be/E9lYHIAZeTc?t=19m25s

Sound good everyone, I will order some more and let you know when they arrive.

Thanks

Lee

[shailesh3t]

i already have the board and its a nice i recommend , already soldered some of the parts awaiting some other parts which are on backorder, will try to post some picture of it
regards and thanks to Mr Wigman

[wigman27]

Hi all!

My new boards have arrived, they are $10 each plus postage.

If you are interested please send me a personal message to arrange payment and shipping.

Thanks

Lee

[f1rmb]

Hi,

Hi all!

My new boards have arrived, they are $10 each plus postage.

If you are interested please send me a personal message to arrange payment and shipping.

Thanks

Lee

PM sent.

Cheers.
---
Daniel.

[Sjokolade]

PM sent.

[wigman27]

Hi all,

As these boards are selling like hot cakes!! Thanks everyone!! I have decided to put them on tindie to make selling them a little easier and easier to keep track of!

https://www.tindie.com/products/Wigman27/pcb-for-arduino-programmable-constant-current-power-resistance-load/

Those that have already paid these have been shipped do you don't need to reorder, any new orders will be processed through tindie :-)

Thanks all!

[snooky]

Thanks Lee, mine arrived today safe and sound.

[wigman27]

Hi all,

I have decided to start working on a revision C. The list of improvements to be investigate are,

• Fully simulate then test the AD8360 as a replacement for the lm324.
• Look at replacing the relay switch over with an OR based system.
• Amplify IOUT to make better use of the of the ADC resolution.
• Redesign the board to better suit an enclosure.
• Move to an SPI based TFT screen or graphic LCD for a more user friendly display.
• Incorporate reverse polarity protection for the inputs.
• Upgrade to a PWM based fan.
• Improving USB isolation.
• Improve analog and digital ground planes.

These changes are still being investigate and will be quite a while off implementation. If anyone has any suggestions then please reply with your suggestions.

Thanks

Lee

[f1rmb]

Hi Lee,

    Few suggestions:

• Switch to another AVR, e.g. 2560, 32k (even without bootloader) is a little small to improve software features (at least for my alternate code). Also, TFT support will suck a lot of flash space. Sure, an extra chip will be required for USB link (who said FTDI ?  )
• Use two free-up pins to add support of an INPUT relay.
• About the PCB drawing, it would be great to add some footprints for external connections for the MosFET (I personnaly use two in //, externally bolted on a huge heatsink), temp sensors and hi power 0.1R resistor (all these parts are also bolted on that huge heatsink).

Of course, it's only my 0.02$

Cheers.
---
Daniel

[jayx]

Hi all,

I have decided to start working on a revision C. The list of improvements to be investigate are,

• Fully simulate then test the AD8360 as a replacement for the lm324.

Hi Lee,

 I think you've meant AD8630? Could you explain a reason for this change please?
Anyway great project

Regards
Adam

[wigman27]

Yep, that's what I meant sorry :-)

The main reason is better offset voltage. There are a lot of other things to consider with the Opamp but that's my main reason for the upgrade.

I haven't done muck work on this yet I'm afraid but a couple of people have helped tremendously in another thread helping me workout the feedback compensation so as soon as I have time I'm back on it :-)

Thanks

Lee

[f1rmb]

Hi,

    Here is a picture of the "finally" finished DC Load.

Cheers.
---
Daniel

[dparson]

wow, beautiful job f1rmb!   

[Rubi]

Hi

I received my pcb today and will build one this weekend.
I have to investigate but I would prefer a graphical oled display, altough they are way smaler, the readability is highly improved.
I plan to use one like these:
http://www.ebay.at/itm/141370921574?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Since it is a graphical display there is also the possibility to display graphs f.e. to display a battery discharge curve.
I will investigate if there is enough processing capability left in the microchip to use one.

Anyhow, very nice design, thank you for sharing.

Cheers
Michael

[f1rmb]

wow, beautiful job f1rmb!   

Thanks ;-)

[chefkoch84]

Hi all,

Nice project, thanks a lot for sharing!!!
I also just right now ordered the PCB and am looking forward to build this thing.
Is by any chance anybode in Germany / Europe planing to also order the parts? We could just bundle up and share shipping costs.

Greetings
Max

[SaabFAN]

Hi all,

Nice project, thanks a lot for sharing!!!
I also just right now ordered the PCB and am looking forward to build this thing.
Is by any chance anybode in Germany / Europe planing to also order the parts? We could just bundle up and share shipping costs.

Greetings
Max

I might be interested. I need a programmable load along with a signal-generator, 30W Amplifier and a power-supply to complete my test-bench.

[chefkoch84]

Hi all,

I finally ended up ordering most of the components at Farnell (here in Germany).
Once you figure out to replace components to similar from Europe stock the shipping went down to a reasonable price after all.

I am happy to share the "shopping chart" if somebody is interested - perhaps drop a PM

Greetings
Max

[chefkoch84]

perhaps this is commonly known and it was a trap for young players but:

HERE COMES THE RANT:
 
The little f*ckers at farnell/element14 make you fill out and optimize your bill of material.
- You optimize all the stuff for some hours.
- They ask for your credit card
- They ask for your name
- They take your order and tell "Vielen Dank - Ihre Bestellung wird bearbeitet"

#########################################################

AND THEN THEY DO NOTHING - AND EVEN DO NOT TELL YOU THAT THEY DO NOTHING

#########################################################

If you finally managed to call them (their official German number is not helping there)
They come up with "we do not sell to private people..."
I asked if they sell to students, since thats a rumor in their own "community"

farnell:" no - not anymore. Just for previous customers"
I: " I bought something at your company previously"
farnell: " but your account gets disable after some time "

They have fucking press releases that they sell to private people. They published those when raspberry pi was released and the nerds in Germany where concerned that they will not be able to get one.

The sades thing is: they apparently do not deserve my ~100 EUR... but because they wasted this amount of time till now I will order there via a company.

cheers
Max

[mikron]

Hi Max,
I know exactly how you feel.
You could try www.hbe-shop.de (a Farnell reseller)...

[PeterFW]

The sades thing is: they apparently do not deserve my ~100 EUR... but because they wasted this amount of time till now I will order there via a company.

That is very, very common.
Sourcing parts in germany is a nightmare if you are not a company.
(Ja... es gibt Kleingewerbe, Nebengewerbe, Gewerbescheine, bla... bla...)

Either they do not sell to you, they demand ludicrous shipping costs or you have to order a bajillion of parts.

[wigman27]

Hi guys,

I'm really sorry you're finding it so hard to get parts.

The next rev I'm hoping to sell as a kit so it should help with this issue.

Sorry again

Lee

[chefkoch84]

Hi Lee,

We all appreciate the fact that you shared the design at the first place.
Additionally you came up with a really nice and in depth documentation and explanation of your thoughts during the design process. I already learned a lot from that - even without building the thing.
You should not even consider to mention the word "sorry" for your awesome work.

To sum that up: THANK YOU

Just for your information to all the others: I finally was able to purchase those parts from farnell here in Germany.
You have to know somebody running a company who is willing to order this stuff for you; you basically need a "Umsatzsteueridentifikationsnummer"  ( nice German word, isn't it? ... just tease us a little bit on that... it's always good fun)

Greetings
Max

[senso]

The sades thing is: they apparently do not deserve my ~100 EUR... but because they wasted this amount of time till now I will order there via a company.

That is very, very common.
Sourcing parts in germany is a nightmare if you are not a company.
(Ja... es gibt Kleingewerbe, Nebengewerbe, Gewerbescheine, bla... bla...)

Either they do not sell to you, they demand ludicrous shipping costs or you have to order a bajillion of parts.

Mouser.com over 65€ its free shipping and they take care of the customs, just pay around 19.x% VAT and its in your home in 2-3 days.

[PeterFW]

Mouser.com over 65€ its free shipping and they take care of the customs, just pay around 19.x% VAT and its in your home in 2-3 days.

Yes. 19% MwSt on top of 40 Euro in parts i do not need, because i just wanted a few ICs and resistors worth 20 Euros. Most likely one or the other part only available on a reel.

Trust me, i am not new to this... in the end the 50 Cent (soq) part costs 5 Euros once it is on my desk.
And yes, i know what samples are, last one was 3 weeks.

[con-f-use]

I can recommend mouser as a farnell alternative. Way better. Parts are at my door within four weekdays despite their warehouse being in the US. Suppose they're are a day faster for German adresses seeing their shipments come in through Köln via  Charles de Gaulle. I've complained in a dedicated thread about farnell. And of course they only sell in quantities and charge extra for small orders. Everyone does and it is econmically and environmentally sound. I would not want it any other way. You can almost always plan ahead and accumulate stuff.

[Sjokolade]

Can you set a cutoff voltage on this load? I'm interested in testing batteries and cell health, it would be helpful if the load didn't undercharge them.

Hey Mate

Currently the software doesn't allow it but it is certainly possible! It is able to sense the input voltage and you would be able to write a small piece of code to not let it go below a certain voltage without too much trouble at all. I might even add it to the next software review list

Thanks

Lee

Hi Lee

Did you add this feature to the software and is it possible to download the new version from you  ?

Thanks

[wigman27]

Hi,

No, not yet I'm sorry :-( I have been held up on other things

[PeterZ]

I got one of these PCBs from Lee lately (thanks!) and started to mod the design a little bit.
So far i have done this:

[PeterFW]

I got one of these PCBs from Lee lately (thanks!) and started to mod the design a little bit.
So far i have done this:

Photobucket is not the best solution to share images, can you upload them somwere else?
I can not see them.

[anker_by]

Very nice project, I will study more.. 

[PeterZ]

Photobucket is not the best solution to share images, can you upload them somwere else?
I can not see them.

Ok, i'll try to attach them.
The main changes for now are:
1. Switched to 1.8" ST7735 128x160 TFT display. It's one of those cheap displays from *bay/Chinese sellers. It can be powered with 5V, but the data lines require 3.3V signals. The usual "arduino style" approach (adding 1k resistgors in series) unfortunately ruined the SPI clock signal, so i added a small level translator built around TXS0104.
2. New GUI, work still in progress. Most likely i will redo the whole menu system and add more functions, like mentioned earlier cutoff voltage. Flash size will be the limit here.
3. Added median filters to Vin and I measurements.

[AudioplatinumService]

Hi,
This is very nice upgrade. Can you share the code and custom wiring?

Cheers,
Damir

Sent from my LG-H960 using Tapatalk

[PeterZ]

Sure, as soon as i finish the project. Or at least get to the point when it will be worth sharing.

### Update 06.2016 ###
Meanwhile the number of changes, hacks and tweaks reached a critical point where i decided to start (almost) from scratch. I'm going to stay within the Arduino enviroment, just for the sake of making a project with it (never really been into all that *duino stuff). I moved over to Teensy LC, which is an Cortex M0+ MCU with 64k of flash.
Boards arrived today and i couldn't resist to populate one.

[silva3rafa]

Question, if i were to change the lm324 for the ad8630, would i need to alter the circuit?
Also when you talked about input protection what kind were you speaking of? just simple inverting input protection?

i am making my own version using a pic microcontroller btw ^^

p.s. what does the 2.2 ohm resistor in series with the 2.2 uf capacitor do?