In this post I will show you how to flash Christmas lights by the serial port. Now you can with Holiday232. This serial port can switch between 4 different lights by using 2 SPDT relays and both RTS and DTR of the relay. As you may be wondering when looking at the schematic why I’m using transistors and resistors. It is because the serial port voltage is higher than 12vdc. I don’t know what the forward voltage or current plus since there is a LED in series with the optocoupler.
The following things are required(for both DTR and RTS):
- 1x RJ45 To screw terminals
- 2x NPN transistors for 4-lights
- 2x 10K resistors for 4-lights or 1x 10k resistor for 2-lights
- 1x 2-channel relay module for 4-lights
- 2x Duplex Outlet for 4-lights
- 1x Cisco console cord. Serial or USB DO NOT GET THE DB9 TO RJ45 FROM ALLELECTRONICS, THE DB9 TO RJ45 CORD THERE ONLY USES THE DATA WIRES
- 1x USB A-B(You will need it even if you get the USB Console cord) You don’t need this for the 2-light configuration(only for the four light configuration) You will cut the cord in half and use Red(+5vdc) and black(Ground) wires.
- 1x Dual gang Outlet box
For 2-lights circuit you will need:
- 1x RJ45 to screw terminals This one is from ebay to save money on shipping. Also on this one the pinout may be different colors.
- 1x cisco console cord Serial or USB
- 1x diode(any rectifier/switching diode will work)
- 1x Adafruit power switch tail Simple connect + through a diode DTR or RTS and – Ground
| Wire color RJ45 screw termnal | Name(DB-9 Side) |
| Yellow and Black(3 and 6) | Transmit and Receive. Tie together so it makes it easy to find the serial port(2 and 3) |
| White(7) | DTR(4) |
| Brown(8) | RTS(7) |
| Red and green(4 and 5) | Ground(5) |
Circuit Simulator