Lego NXT 240V A.C. Appliance Controller    Send article as PDF   
This Lego Mindstorms NXT Appliance Controller allows you to turn on-and-off your Household mains powered equipment such as lights, radios, heaters, etc. All via your Robot. Using this Controller in conjunction with a Lego Temperature Sensor you can control your aquarium, and even as a incubator control to hatch out bird eggs.
This project needs a lot of care during construction due to the Voltages involved.

120-240V A.C. KILLS!

Only for experienced hackers!


The appliance is switched on and off using an Optically Isolated TRIAC (Electronic Relay) to safe guard the NXT from damage. You treat the controller as a standard Lego Light Sensor. The controller uses the software toggling as used for a standard Lego Light Sensor LED switching from reflected to ambient light sensing.

SSRAC – Solid State Relay Board

I discovered it was easier and cheaper to buy the fully assembled SSRAC SOLID STATE RELAY Board off of eBay, than spend the time making the PCB and all the associated fiddling around. The completed module cost only twelve dollars, including Postage and Handling.

As can be seen from the circuit diagram, even if you decide too build the controller it’s a simple construction for  vero or strip board. TRIAC’s are extremely effect and reliable. With the small heat-sink fitted on the module above it will happily conduct 240 Volts A.C. at 10 Amps producing very little heat. The NXT is protected via an Optically Isolated TRIAC Driver which keeps the high voltages away from the NXT should the TRIAC fail.

I have now put the Mains Appliance Controller in a suitable box, using an old plug pack base for A.C input and an IDC Socket from an old PC power supply for the A.C. output. I also put a 10 Amp fuse in the A.C. active line from the controller to the output socket for a bit of extra protection. I decided on a simple Fly-lead to connect to the NXT with.  There’s also an red LED on the outfacing side to show when the output is active. All up, the Lego Mindstorms NXT 240V A.C. Appliance Controller will set you back around $20 and an hour in the shed.

Finished Lego NXT Mains Appliance Controller

On another rainy day I might use a PCF8574 I2C chip. with 4-8 TRIAC Controllers attached to make an NXT Music Colour System that flashes flood lights in time to music. 20+ years ago I build quite a few Music Colours for local D.J.’s to use with their P.A. Systems. The were very popular back when DISCO was king!!

Lots of possibilities ………………..

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