Josef Adamčík

Freeform ESP8266 OLED MQTT client

May 20, 2019
4 minute read

My second freeform creation, or third if we include The CyborgDuck is here. I wanted to do something simple in order to gather more experience and improve my skills.

This article is Part 1 in a 3-Part Series.

Circuit

When I was thinking what to build as a next, simple free-form circuit, my eyes fell on my RoomMonitor project (link is to a GitHub repository with its firmware). That’s one of my long-running projects. Basically, a bunch of sensors connected to ESP8266, battery powered, measures conditions in a room and sends data to some online service via MQTT. Nothing that much interesting. The challenge here is to make it last as long as possible on a battery. It might evolve into a weather station in the future. Right now, I am running the second prototype and planning the third one. Then, maybe, I might think about making some final form for that.

But since this is a battery-powered device and the micro-controller sleeps most of the time, there’s no display. I have always planned to make another device which would act as a remote display of sorts.

The idea is simple:

  • Use ESP8266 again, I have plenty of them and know them well enough.
  • Use a small OLED display and show only one value (temperature).
  • Powered through a USB connector, since I have plenty of USB power sources. But that also means I need to step-down the voltage from 5V to ~3.3V
  • Include LED which would indicate low battery voltage on the RoomMonitor device.
  • Have some touch-like input which would allow to cycle values on a display or similar.
  • Have a way how to program the ESP8266. For the firs firmware upload and for emergencies, when over the air update fails. Normally OTA should be used since it’s easier than connecting FTDI every time.

Since I am very new to free-form, I wanted to have the construction as simple as possible. Therefore, I decided to:

  • try to do most of the circuit in flat layers which would be easier to solder together,
  • use simple shape - cube or cuboid,
  • use PCB breakouts for some things - OLED display module, USB connector, and LDO.

Here’s a schematic for the final circuit (available also on EasyEDA).

Schematic

The top part is the power layer - a USB connector and a LDO regulator(LT1763) connected according to the datasheet.

The bottom part is the top layer with ESP8266 and LED. The OLED display is not in the schematic, but it’s connected via I2C. The schematic for the ESP8266 is based on the one you can find here. I have only added buttons for Reset and Flash, LED and another capacitor.

I quickly prototyped everything on a breadboard and drafted a (still not finished) firmware.

Once I figured out the layout I created templates in Inkscape and started building.

Material

The main material for construction are 0.8 mm (1/32) brass rods. I bought mine from Modulor.de (a German e-shop). But you should be able to get them from your local hobby&model shop. Sometimes they are available on Amazon too.

Those are used by other people (mainly Jiří Praus and Mohit Bhoite) so we could consider them to be the ‘state of the art.’

They can be a bit harder to solder, so add some flux and use a decent soldering iron. Check out this very nice guide guide to soldering brass.

Build log

A template for the first layer, already soldered frame and working on the ESP8266.
A template for the first layer, already soldered frame and working on the ESP8266.
The first step finished. The frame will act as ground, diodes are used only for structural purposes - they help to hold the VCC rail in place.
The first step finished. The frame will act as ground, diodes are used only for structural purposes - they help to hold the VCC rail in place.
Cardboard proved to be very helpful.
Cardboard proved to be very helpful.
Soldering the connector for an FTDI in order to allow programming. I also used a bit of superglue to attach the plastic side of the connector to the brass rod. It will be used for the first firmware upload and for emergencies. An over the air update will be used for regular updates.
Soldering the connector for an FTDI in order to allow programming. I also used a bit of superglue to attach the plastic side of the connector to the brass rod. It will be used for the first firmware upload and for emergencies. An over the air update will be used for regular updates.
Another way how to utilize cardboard...
Another way how to utilize cardboard...
Here to ensure a nice clearance for a resistor crossing a few other wires.
Here to ensure a nice clearance for a resistor crossing a few other wires.
And the result. This is actually enough to connect and program the ESP8266.
And the result. This is actually enough to connect and program the ESP8266.
Power & programming test, it worked!
Power & programming test, it worked!
Working on the bottom layer - the power source. Yes, I am not brave enough to attempt to freeform an SO8 package of the LT1763 LDO regulator, so I used a breakout.
Working on the bottom layer - the power source. Yes, I am not brave enough to attempt to freeform an SO8 package of the LT1763 LDO regulator, so I used a breakout.
Flipped around, added an USB connector - breakout version again.
Flipped around, added an USB connector - breakout version again.
And capacitors, of course. Exactly how it's suggested in the datasheet.
And capacitors, of course. Exactly how it's suggested in the datasheet.
(Sorry for a very ugly photo.) I almost forgot to add buttons for reset and flash. Maybe not necessary, but I chose to include them.
(Sorry for a very ugly photo.) I almost forgot to add buttons for reset and flash. Maybe not necessary, but I chose to include them.
Prepared wires for legs and I2C lines.
Prepared wires for legs and I2C lines.
Trying to figure out how to solder I2C lines. Cardboard helps, again.
Trying to figure out how to solder I2C lines. Cardboard helps, again.
Template for the front side with an OLED display and a LED. The top layer is already connected.
Template for the front side with an OLED display and a LED. The top layer is already connected.
Added the backside...
Added the backside...
...and the bottom layer. Now let's solder all together. This was the most difficult part.
...and the bottom layer. Now let's solder all together. This was the most difficult part.
And done! Complete, neater than I expected and working.
And done! Complete, neater than I expected and working.
Another angle...
Another angle...
...and another.
...and another.

This article is Part 1 in a 3-Part Series.

Looking for comments? There are no comments on this website, at least for the time being. But If you feel you would like to say something, send me (josef.adamcik@gmail.com) an e‑mail, please. I might even publish a resulting conversation as an update to the post, if it's worth it.