Equipping a microservo with Crocodile clips

If you are conducting a class or group activity, you should consider preparing all servos ahead of time.

Using a microservo with the micro:bit

The micro:bit provides just enough current to operate the SG90 microservo. This servo requires 3 connections: GND, 3V and a logic pin. In this tutorial, we will equip the servo with crocodile clips to make it easier to use. However, you could also use a shield or crocodile clips with a male connector on one end to achieve the same result.

The easy way: Alligator/Crocodile Clip to Male Jumpers

The easiest way to connect a servo to the micro:bit is to use cables with an Alligator/Crocodile clip on one end and a Male jumper (pig tail) on the other end. You can purchase bundles these cables from various electronic resellers or easily build some as shown here.

Materials

  • 1 Crocodile clip cable
  • 1 male (pig tail) cable
  • Cutting pliers or wire cutter
  • 1 piece of heat shrink tubing and a lighter

Simply cut the cables, strip them, twist the bare wires together, and cover the connection with some heat shrink tubing.

It is very important to ensure a good connection between the 2 cables. If the connection is weak, the microservo will not receive enough current and it will not work. If you have access to a soldering iron, we strongly recommend that you solder this connection.

Direct connection

You can also connect your crocodile clips directly to the servo.

Materials

  • Cutting pliers or wire cutter
  • Tape (masking, duct tape, and/or packing tape)
  • 3 crocodile clips, yellow, red and black.
  • 1 micro servo 9g (SG90)

Step 1: Cut off the connector

With the cutting pliers, cut off the dark plastic connector.

Cutting of the plastic connector from the servo cable

Step 2: Strip the ends of the cables

Using the pliers or a wire stripper, strip the plastic insulation from the cables.

Stripping the servo cable insulation

Step 3: Twist the wire strands together

Twist the strands of bare wire at the ends of the servo cables together.

Strands of the servo wires twisted together

Step 4: Crocodile clip

Cut a crocodile cable in two and strip off the insulation. If it’s possible, try to use cables with colors that match the cables on the servo!

Stripping insulation of a croc cable with cutting pliers

Step 5: Thread the cable ends together

Place the cables next to each other…

Bare wires place together before threading

… and thread them together.

Bare wires threaded together

It is very important to ensure that there is a good connection between the 2 cables. If the connection is weak, the microservo will not receive enough current and it will not work. If you have access to a soldering iron, we strongly recommend soldering this connection.

Step 6: Protect the connection

Protect the connection with heat shrink tubing, electrical tape, or duct tape.

Wire connection protected with electrical tape

Step 7: Repeat for all cables

Repeat the same process until all cables are connected.

All three cables connected and taped

Step 8: Testing!

It’s time to test and find out if your connections are all secure and that the servo will function when the micro:bit is powered by battery.

  • Connect the microservo cables to these pins on the micro:bit: black to GND, red to 3V, and the remaining cable to pin 0.

Connect to the pins on the board

When attaching the crocodile clips to the pins, don’t be afraid to clamp on to the edge of the board with the clips.

Clippiing the cables to the edge of the board

  • Download the following code to your micro:bit.
basic.forever(() => {
    pins.servoWritePin(AnalogPin.P0, pins.map(
        input.acceleration(Dimension.X),
        -512,
        512,
        0,
        180
    ))
})
  • Test with both power sources and make sure that the servo moves when you tilt the board:
    • Connected with USB.
    • Powered by batteries only and not connected with USB.

Calibrating

Use the servo calibrator program to determine the best angles to use for your make.

Troubleshooting

If your servo seems to stutter and remain stuck at a particular position, it means that it’s not receiving enough power. This is probably due to a weak connection or low battery level. Make sure that each connection is good and check your batteries.