When developing a network-enabled project with the ESP8266 or ESP32, the easiest way to handle WiFi credentials is to just hardcode the access point and encryption key into the program. But that means recompiling the firmware if you ever want to use it on a different network, which isn’t really an option if you’re trying to make something that other people can easily use. If you’re expecting grandma to bust out the UART cable, we’ve got bad news for you.
There are various ways around this problem, but we think the one developed by [Pekka Lehtikoski] is particularly clever. With a simple application, network credentials can be literally “flashed” to the waiting microcontroller by rapidly blinking the flash LED on an Android device. This allows the information to be transferred quickly and easily regardless of the user’s technical proficiency. One could even make the argument that it’s more secure than some of the other methods of doing initial setup, since an eavesdropper would literally need to see you do it if they wanted to steal your encryption key.
[Pekka] has made the source code for the Android application and the “Gazerbeam” library open for anyone who wants to include the capability in their own projects. To pick up the blinking light you just need to add a phototransistor, an opamp, and a handful of passives to your circuit; making this solution cheap enough that you could even use it in a small-scale production run. The concept isn’t limited to network credentials either. Whenever we can hold conferences again, it could be an interesting way to let attendees customize their badge.
Of course, [Pekka] isn’t the first person to use this trick. Hackers well versed in the history of WiFi MCUs may recall that the Electric Imp used a very similar method of configuration called BlinkUp. If you ever come across a device that asks you to put your phone’s screen down on a little window to perform the initial setup, there’s a good chance it has an Imp inside.