Cinema Display LED control with 9V-12V ESP8266 Web Switch

I picked up one of the A 4 Cinematic Light Box devices to use as a team sign in an Agile Program Increment planning meeting.  The unit requires 6 AA batteries. That seemed wasteful so I added a 9V barrel jack to it to power it with a 9V wall wart.

The next step in turning a $15 box into a $40 project was to add an ESP8266 relay board to enable WiFi control for the sign light.  My controller is ESP8266 Link Sprite LinkNode R1 that was locally available at Microcenter for $11.

Basic Circuit.

The basic idea is to turn the ESP8266 into a 9V switch that needed no external power. I wanted to tap the 9V intended for the display LEDs and drop it to 5V to run the ESP8266 without need of a 2nd power source.

Two diodes tap power from either jack and sends it to the ESP8266 and relay circuits.  It doesn't matter which jack is used as the inbound power source and which as the outbound to the display. Either will work because of the two diodes. They are arranged a way that doesn't limit which direction current flows through the relay.

Fritzing didn't have any LinkNode devices. The relay and WeMos in the Fritzing diagram are actually on the same LinkNode board.


The whole circuit, regulator, control board , diodes and jack all fit within a Mentos tin.

I was worried about wifi reception but that isn't an issue with my target location.

The final design uses a UBEC switch mode DC regulator intended for R/C devices. That regulator accepts 5.5V to 26V inbound that it converts to 5V outbound. This means the device actually acts as a self powered in-line switch for any circuit 5.5V to 26V
  • ESP8266 board with relay
  • 2 panel mount barrel sockets.
  • 1 UBEC regulator
  • 1 Mentos tin
  • 2 Diodes

Input / Output

The two barrel jacks act as input and output ports. The ports are "joined" through the actions of the relay.  Either port can act as either input or output.


Source code for this project can be found on GitHub:

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