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Discontinued   Relay       $39.00              

This product is no longer being built by Techno-stuff. 

The web page is here for reference only.

This sensor has been tested with NXT using the Lego NXT conversion cable (W770323).

Control other electrical devices from your RCX.

(Contains two SPDT relays)

A relay is an electric switch controlled by an electromagnet. You can use a relay to turn on electrical devices that do not attach directly to your RCX. For example, you could use a relay to run a tape recorder from your RCX.

The relay brick connects to a motor port on your RCX. Applying full power to the motor port will activate the relay.  

The Techno-stuff relay brick is actually two relays in one package. The brick connects to one motor port on the RCX. You select which relay to activate by selecting the motor direction. Only one relay can be active at any given time.

Each relay has one normally open contact, and one normally closed contact. When the relay is activated, the normally open contact closes, and the normally closed contact opens. By choosing which contact you use, the relay can either turn on or turn off a device when it is activated.

Relay brick for Mindstorms


Connector for Mindstorms relay control

Relay connector block.


The relays are activated through a motor port. The motor port must be set to full power. The relay is only active while power is applied. Reversing the motor direction will activate the other relay.

Example: HO train

The relay brick can be used to control HO and N scale 12 volt trains. When a non-latching relay brick is wired as shown below, setting the RCX port to the forward direction will cause the train to go forward. Setting the RCX to reverse will cause the train to reverse. Setting to RCX port to stop will cause the train to stop. Use this technique whenever you need a polarity reversing switch.

Schematic for RCX relay



•  Brick Size: 3 bumps by 4 bumps.  Height is one and two thirds bricks.  (one brick plus two flat plates). Overall size:  1.25 x 0.95 x 0.68 inch.

•  Mindstorms black electric connector on 6 inch (10 cm) cable.

•  6 pin compression screw connector for relay terminals.

•  Two relays, each SPDT

•  Maximum contact current: 2 Amp.

•  Maximum contact voltage: 48 volts.

•  Current from motor port: 16 mA.

Technical Description

The relay brick contains two SPDT relays with 9 volt DC coils. Each relay coil is connected to the RCX through a diode, so that the RCX wire polarity selects which relay is activated.