A TFB reader purchased a damaged EOTech very cheaply, then gutted the internals and replaced them with custom electronics. This video shows the result:

The possibilities are endless. Rangefinders, shot counters, timers etc. could be easily integrated and the data shown on the Heads Up Display (HUD).

It was built using a Arduino Pro Mini (about $7 on Amazon), a small variant of the popular Arduino micro controller board, which was squeezed into the battery compartment. The Arduino was wired to the EOTech’s switches and to a cheap I2C OLED display (about $5, search eBay for “i2c oled”). The OLED display replaces the laser module to provide the HUD/reticle. One neat advantage of using the OLED is that the HUD can extend “beyond” the users field of view, allowing the user to look through the scope at an angle and see additional information. The downside of the OLED is that it is not nearly as bright as the EOTech’s laser module and is faint in direct sunlight. A field ready version of this hacked EOTech would need a significantly brighter display.

I asked the reader if he was willing to share the custom code he wrote which runs on the Arduino, but he said it was very rough around the edges and not worth sharing with the world.