The project outlined in the previous blogs seemed to work well. It was time to make a PCB and put some finishing touches on the software. The PCB is roughly the same size as the Doit ESP8266 board. To keep the size down, I have almost exclusively used SMD components. Over time, I have been slowly trying to switch over from through hole to SMD.
While building it on the breadboard, I used through hole equivalents of all the passives. The components that did not have a through hole equivalent were the IR LED and the WS2812B. A few wires soldered to them fixed that problem. I had a bunch of WS2812B that come mounted on to a PCB. This made soldering the wires a lot easier.
Moving to a PCB with SMD, the only component that still had to be through hole was the TSOP38238. The leads are bent over to keep the profile low and point the sensor in the right direction.
I ordered the PCB through Seeed. It has a low cost PCB option as long as you stay within some limits. In order to keep it down to the low low price of US$5 for 10 PCBs, the constriants are:
- The thickness is 1.6mm or lower. As the PCB is quite small, just for the heck of it, I went for a 1mm PCB
- Quantity is 10. This is a bit weird - if you need 20 pieces, you are better off splitting it up into two orders and paying $10 instead of $43!
- PCB colour is not an issue
- Everything else is. Fiddle with it and the cost is 10x.
This is what the fully assembled PCB looks like when mounted on the back of the ESP8266 board. A single USB cable is the umbilical cord to the assembly. It is the connection for power, for flashing the ESP8266 and for a serial debug port. During development, it is plugged into a USB port on a laptop. In normal operation, a USB charger can be used to power the board.
My transition to SMD is not complete. Soldering the components to the PCB was not easy but the results are not too bad. It was only when I started soldering the components on that I realised that my collection of resistors was not complete - I replaced the 2R2 with a 4R7 resistor but it still seems to work fine. I also realised that my SMD resistor collection was 0805 and not 1206 as I thought. I was able to just about use them but a new batch of SMD 1206 resistors is on order. Also, if you look closely, I did not solder the PCB to the ESP dev kit - it is just pushed on. It is a bit hacky but it seems to work fine. It also allows me to reuse the dev kit if I feel like it.
The project seems pretty complete and can be the basis for further work. This may be a good time to release the details. The files are also on github.
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