The goal of this project was to avoid waiting at the tram-stop in sub-zero temperatures, which would be achieved by having a constantly-updating display showing the next departure time from our local tram-stop.
If there is a tram due in a couple of minutes we could leave the house in safety, if there was a wait of 10+ minutes we'd stay indoors.
The hardware for this project is simple:
- 1 x WeMos Mini D1
- Approximately cost €2.50.
- 1 x Push-Button
- Approximate cost €0.05.
- 1 x I2C LCD Display
- Approximate cost €1.50.
- We've previously documented using an I2C LCD with an Arduino.
- In my project the display was initially 2x16, but the code allows for different dimensions.
- I soon upgraded it to a 4x20 display instead, as pictured below.
Wiring merely consists of connecting the display to the Mini D1 board, which is in turn powered by a simple USB-PSU, then adding in the push-button as an optional extra. The display-wiring is as follows:
- Vcc -> Vcc (3.3v)
- Ground -> Ground
- SCL -> WeMos D1 D1
- SDA -> WeMos D1 D2
The push-button is connected between D0 & D8, and is entirely optional
The initial setup looked like this:
Then I added the optional button between D0 & D8:
Finally the project was fitted into the box I had 3d-printed:
If you've previously configured WiFi details the device will connect automatically to your local network and begin working:
- Updating the display once a second.
- Resyncing the time, via NTP, every five minutes to avoid drift.
- Serving a simple GUI via HTTP
- This mirrors the output shown on the device screen, as well as allowing changes to be made, for example:
- Controlling the backlight.
- Changing the tram-stop being monitored.
- Changing the TimeZone offset (i.e. This project is for Helsinki, so we're at
GMT + 2or
The optional button allows some immediate actions to be carried out, without reaching for your mobile device :
- A short-press
- Toggles the state of the backlight.
- A long-press
- Triggers an immediate resync of the date & time, as well as the tram-data.
If you've never configured the device before it will begin to operate as a WiFi access-point - you can use your mobile phone, or other WiFi-connected device, to connect to this access-point and setup the local WiFi network it should join.
Thanks to the web-based GUI the project does not need to be recompiled to change the networking details, or any of the other configuration settings!
The software for this project is divided into a few distinct parts:
- Handling connections to the local WiFi network.
- You need an IP so you can connect to the internet to fetch the timing details.
- Fetching the current date & time, via NTP.
- Drawing that date & time.
- Fetching the tram-time for the local tram-stop.
- Drawing that data.
- Allowing over the air updates, directly from the arduino IDE.
- Handling input from the optional button.
For dealing with the date & time, including retrieving the current time via NTP, I used the standard time library, which has excellent support for such things. The web GUI allows changing the time-zone, which is necessary if you're outside GMT.
Retrieving the departure-times for a given tram-stop is pretty straight-forward, but to isolate the device from changes I setup an API-proxy to handle retrieving departures:
By default the first line of the display will show the current time & date. However other display-modes are available, and can be selected by pointing your browser at the IP address of the device:
- Show the time and date.
- Show the time and current temperature.
- Unfortunately this is hardcoded for Helsinki at the moment.
- Perhaps forgiveable given the nature of the project.
- Show the time, and alternate between date/temperature display every 10 seconds.
- Show a fixed message
- For example "Happy Birthday!".
Several libraries are used, and these are bundled together in a git repository, you can access all the source by cloning the repo involved, and then looking at the project:
The code has become a little more complex over time, especially since the addition of the web-based user-interface, but if you have any questions feel free to ask away.