littleBits modules are very accommodating - they will hook up to almost anything. With one notable exception - Lego's Mindstorms EV3 robot kits have their own system - it's similar to I2R, but different enough that it's very difficult to communicate with from outside the EV3 ecosystem. But their motors and sensors are really interesting - I want to use them in a littleBits project, but until now, I've had little success.
In order to hook my EV3 to littleBits, I used the same technology as in my Klein Bottle project
: one half of the system is inverted and fead back into the other half. In this case the littleBits half pushes the EV3's button, which in response pushes the littleBit's button.
Here's the littleBits schematic:
p3 - i3 - w1 - i17 - w10 - o11 - o2
The EV3 brick has a touch sensor attached to input port 1, and a medium motor on output port D. The two devices are juxtaposed using the Lego stuff that comes with the EV3 student kit. Look at the pictures to see how the motors interact with the buttons.
Let's follow a button press:
- * The littleBits button is pressed for about a second, which emits a pulse from it's output.
- * The pulse goes through a wire to a timeout bit. The timeout is set just slightly longer than the minimum (which is no delay), and in off-on mode.
- * When the pulse escapes the timeout it is inverted, and sent to a servo motor.
- * The inverted pulse moves the motor to press the EV3's touch sensor (it's a button.) When the pulse ends, the motor returns to its 'not-pressing the button' position.
- * Pressing the EV3's button triggers the medium motor to turn forward then backward. This motor is attached to a screw gear which moves a plastic rod about a centimeter forward, then back to it's starting position. The round trip takes a little over a second.
- * The rod is positioned directly above the littleBits button, so that when goes through one reciprocation, the littleBits button gets pressed.
- * Repeat.
This just keeps happening until I pull some of the wires apart. It's doesn't have an off switch. Power is supplied from the EV3's lithium ion battery. The littleBits take's it's power from the EV3's USB port, so there is no external power connection. The device is also gravity independent - it functions the same in any position, even under acceleration.