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I’d like to use a signal from a (5V) littleBits circuit to control some (9V) Power Functions motors.

Does LEGO sell or recommend a DC relay to facilitate this sort of thing?

If the answer is no, I’d welcome any ideas or experiences in how to do this in a way that’s both easy and LEGO-compatible.

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    <secure.sayal.com/STORE2/View_SHOP.php?SKU=248131> is a relay that can be driven from an Arduino, so I would think it could also be driven by littleBits. But it may require more damage to Lego-supplied wires than you'd like, in order to splice it in. I don't know if it's viable, but could the littleBits circuit move a small arm side to side? If your hand can control the Power Functions using a remote like <bricklink.com/v2/catalog/catalogitem.page?P=58122c01>, then surely a robotic arm could as well. I don't know that either of these count as easy, or Lego-compatible.
    – RSchulz
    Jan 9, 2021 at 0:00

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LEGO doesn't make something to directly facilitate this type of integration as far as I know. If you can get a PF extension wire, you could cut it and directly make the connections to your driver circuit.

PF extension wire

You can drive the motor using the middle wires of the PF cable (C1 and C2).

For what its worth, I would personally prefer an H-bridge such as this one over a relay as you get faster switching and can use PWM for speed control among other benefits. You'd power a board like that using a 9V supply and connect the C1 and C2 power lines to one of the outputs. Your 5V logic-level signals would connect to one set of inputs to control the motor.

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  • I'm not that familiar with H-bridges, but I'm researching the option. Can you tell me if this SparkFun Motor Driver would work just as well as the model you mentioned? (I understand that it may be an H-bridge since it is tagged that way.)
    – EJ Mak
    Jan 20, 2021 at 22:20
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    @EJMak I haven't used that exact driver, but it looks like it should do what you want.
    – jncraton ♦
    Jan 21, 2021 at 3:07

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