Through the past month, I have been trying to build an open source potetionstat/galvanostat as described in a research paper (see here). Knowing that the probability of failure trying to manually solder such small components was high, I ordered some fully assembled PCBs from PCBway one month ago to make sure I had a plan B in case my manual attempts failed.
If you have read my last few posts, this is exactly what happened, I completely failed at successfully assembling this board myself (not the best soldering hand in town!) but thankfully received my fully assembled PCB from China a couple of days ago. The PCB from china worked flawlessly, allowing me to perform the calibration and have a fully functioning potentiostat/galvanostat for home use.
The python software provided by the creators of this potentiostat also worked really well. Using the knowledge I obtained within the last couple of posts, I was able to easily use the drivers provided by the authors to use this software without any issues. The software implements some basic experiments, like CV, charge/discharge curves and Rate testing, but the best thing is that the entire thing is open source, allowing me to customize the experiments to do whatever I want, something I know many researchers wish they could do with the expensive software packages – all closed source – provided by normal potetionstat manufacturers.
This ends my quest for the building of a – now not so much – DIY potentiostat/galvanostat, giving me the functionality of a piece of equipment that usually costs around 1000-3000 USD for just a couple of hundred dollars. Even more, this potentiostat allows me to use current in the -25 to 25 mA range, something that isn’t that common unless you go for the more expensive potentiostats above the 3K+ USD range, since the cheapest potentiostats are usually built for high sensitivity at lower currents – because these are mostly intended for analytical chemistry experiments – rather than for the charging/discharging of battery cells.
My posts will now move onto the experimental batteries I am attempting to build and their characterization. I have always noticed that DIY batteries on the internet are almost never properly characterized – no wonder given how difficult it has been up until now to get access to proper equipment to do so – but with this piece of hardware I will now be able to perform all of these experiments without issues.
With some improved soldering skills I reattempted soldering of all the components into the brand new PCB I had left from Osha Park. After doing this I still experienced a significant amount of shorts but this time I was able to pinpoint the sources by some smoke coming off the PCB (not the greatest sign!). In the end all the shorts were coming from what seems to be the underside of the microchips, probably related with some flux residue that got carbonized and became somewhat conductive after the chips were soldered and the circuit was powered.
With this information I now resoldered all the chips, being very careful about cleaning all the flux to ensure that there were not shorts after the chip was put into place. With all these shorts removed I was able to finally power the board without any excessive current drain.
Due to the fact that the drivers that come with this device are unsigned I had to restart windows using the “Advanced boot options” to ensure that driver signing was disabled. Also remember to install pyusb and usblib before launching the python program.
With this done I was able to successfully connect the PCB to the computer and use the software to interact with it. However after trying to do the calibration I noticed that the entire potentiostat/galvanostat functionality was actually not working and I was actually unable to set any potential without the circuit going a bit “crazy”. As you can see in the image below, everytime I tried to set the potential to some value I just got some random potential being set, with current bouncing all over the place.
Feeling the temperature of the different chips, the one that is overheating seems to be the OPA4192 chip. I tried to remove it and resolder it again, but I have the same problems and the same type of abnormal behavior. Right now it seems that the most likely scenario is that all my desoldering and soldering endeavors have fried one of the components of the board, meaning that I might not be able to get it to work at all with the current components.
Thankfully plan B is still going on – a PCB being fully assembled by pcbway – so I should be able to get a fully working board within the next couple of weeks. I am still debating whether it’s worth it to order new components and try on a new board – with my already gained experienced – but I think I’ll wait for the working PCB to ensure this board works as I expect it to before I make any further DIY attempts.
As I explained on my last post, I want to build a system to characterize batteries at a small scale at my home. This means being able to test things like their coulombic efficiency and measure things like charge/discharge curves. The perfect solution came as the USB potentiostat/galvanostat published in this paper so I order 3 boards using Oshapark and got the rest of the parts from microchipdirect and digikey.
I received my PCB order last week – as shown above – and proceeded to solder the components that I received as well. After soldering all the components I then connected the board to the PicKit3 programmer using the programming leads. By the way, the square pin right below the K3 mark should match pin 1 in the programmer, something that is not mentioned within the above cited paper.
When I did this I used the MPLAB X IPE v5.4 software, downloaded from this link. Using the advanced options I made the PicKit3 provide power to the board and I then proceeded to program it at 4V because when I connected it at 5V I received some erros about VDD not matching between the microcontroller voltage and the provided voltage. In the end I was able to program and verify the chip at this voltage with the hex file provided by the authors of the paper.
After this I then connected the chip into the computer using a USB port and instantly received a USB overcurrent warning, which immediately disconnected the PCB from my computer (uh oh). After checking the board I noticed a short after the charge pumping circuit, where the +9V line was almost shorted to ground, with a resistance of around 10-100 ohm when it should be at least 10kohm given the lowest resistance connected between ground and this line (R2). You can test this by measuring resistance between the leads in R2.
After painfully taking out all the components one-by-one from one PCB and soldering them onto a second one I realized that my problem was that overheating the PCB actually created a short-to-ground in this line, more likely than not related with partial melting of the PCB in the U8 microchip leads where the +9V and ground lines are particularly close to one another. This can actually happen by heating anywhere on the board that’s connected to the ground line, even if you overheat something like the LED D3 or D4 lines. I noticed because I caused the same damage on the second board I was working on, even though the lines were not shorted right before I was working on the D4 LED but became shorted right after I spent around 20 seconds applying heat (yes, my bad).
Right now I sadly only have one board left (sigh) and have already desoldered and soldered a lot of the components. I now need to desolder all the remaining components from these two boards solder them onto the third board, although this case I will need to be especially careful about how I apply heat to the board as I definitely do not want to cause this shorting issue again. I will update this blog after I try again.