Devlog #6: Getting throttled

Attempting to complete my PCBs, and I’m going through it, fr.

Fried transistors + attempted fixes

After receiving my PCBs, I got to work to solder my components. I had ordered PCBA for any components I didn’t have, such as inductors, the barrel jack connection, etc., but I was planning to save money by hand-soldering components I DID already have, such as transistors and my entire MCU system. This also gave me the added benefit of testing these components beforehand, and it allowed me to go through several iterations of code on the ESP-01S.

The first issue I encountered with hand-soldering was with soldering the tiny, microscopic transistor holes (it was my first time doing so). The copper pads for my PN2222 breadboard transistors are super close together, and with my shaky hands, I accidentally whiffed, put too much solder, and left a solder connection between all three pads. Whoops!

I eventually managed to fix it with a solder sucker.
But after soldering, I decided to test the transistors with a multimeter to check if they were damaged, and both transistors were duds. I probably spent too long trying to fix it with the soldering iron and ended up frying them both.

After this, I attempted to salvage the project by desoldering some of the more expensive components from the board and using it on the second backup PCBA I ordered from JLCPCB. I managed to salvage the OLED screen, but while desoldering the ESP-01S, I broke off several pins, essentially leaving the chip unusable. I decided not to salvage the bigger chips (e.g. ESP-01S, ENS160+AHT21), and decided to just reorder some components instead for the second attempt.

New attempt: flip-flop switch fix + MCU not working

I managed to solder all components to the second PCB cleanly, without any hiccups. However, on trying my project out, I encountered two issues:

The flip flop switch turns on the fan, but it doesn’t turn it off.
The 3.3V MCU system (including the OLED, ESP-01S, and ENS160+AHT21 sensor) doesn’t seem to turn on.

The first issue was relatively easy to fix. Turns out, I had forgotten to add a pull-up resistor near the bottom of the flip-flop switch, and thus my steering capacitors had no path to VCC to “refill” (reset) their charge after the initial button press. I quickly soldered a pull-up resistor to VCC to fix it.

The second issue stumped me for a while. I found out that I had forgotten to connect pin 4 (EN) of the ESP-01S to 3V3, so I quickly soldered a connection, but it still wasn’t working. Eventually, I took a look with my multimeter and found the problem: my 3V3 logic chips were actually running on 1.23V for some reason.

It turns out, JLCPCB had sent me PCBA’s with the WRONG BUCK CONVERTER. I had ordered an TDSEMIC LM2596S-3.3, which would normally work perfectly, but JLCPCB had sent me PCBA’s with TDSEMIC LM2596S-ADJ instead.

I’ll have to either contact JLCPCB for a refund, or attempt to salvage the PCB myself by modding it. I’ve burnt enough allowance on this ;-;

Below: desoldering fail, attempted fixes (2), close-up of LM2596S-ADJ vs what I actually ordered (https://www.lcsc.com/product-detail/C42421958.html?s_z=n_q_C42421958&globalKeyword=C42421958)