Some years ago I was at a party where I saw a SMS message board the first time.

Two beamers to each side of the stage displayed messages people could write to a specific phone number. The board said something like “made by fritz”. It sparked my interest and the next day I spent searching for “fritz” and his messageboard, but I never found anything useful, except for extremely expensive offers of companys renting such messageboards. So I went to alibaba and ordered two sim900 boards.

The sim900 is a really nice and incredibly cheap module, but if you order it from china it’s very likely that it comes with an Asian firmware. A friend of mine who already got it running sent me the flasher tool and the European firmware. Since I connected the board using an Arduino serial converter and the software is windows only I had to set up the drivers baud-rate in windows control panel additionally to the flasher tools baud-rate to get it running.

Then I started building the node.js app. I choose node because I wanted to play with it, and it turns out to be incredibly entertaining. Compared to Php or even normal programming in C++ coding a server side app in JavaScript felt like being a little kid playing in the mud =D

I used serialport to talk to the sim900, lowdash to cache the messages on the server, socket.io to push them to the client browsers and emojize to render out the emojis in  css sprites (to make them look the same on Windows and macOS).

For the emojis I also had to set the sim900’s character encoding to UCS2 (UTF-16). Otherwise if you use GSM it will fallback to UCS2 every time you send it an emoji. So now everything is in UCS2 and I wrote a function that splits the encoded message and parse the characters.
 

The full project is on Github.

To install it run “npm install” and set your phone number, the pin and your serial port in the config.json

My SIM module: