BBC micro:bit guinea pig timed feeder instructions

This blog post is the instructions on how to use a timed servo motor circuit that I lashed up as part of a guinea pig feeder for a friend.

The hardware details can be found here: here

Software is on my GitHub site here

The need

A friend wanted something to open a box of food to feed his guinea pigs. The box needs to open after an adjustable time.

I can think of no more noble cause to focus on than feeding our furry friends.

After a period of procrastination and confusion I supplied the hardware and software detailed in this post. The mechanical components that the device will operate are up to my friend to make. He is a highly experienced mechanical engineer. I am but a lowly electronics tech.

Between the two of us, the guinea pigs will be fed!

Description

The microbit counts down for a preset amount of time. The remaining time is indicated on the LEDs on the microbit. At the end of the pre-set time, the servo motor lever moves 90 degrees. The two positions of the servo motor are shown in the pictures below.

The timer is adjusted using the A and B buttons as detailed in the Instructions section below.

Servo motor position while the timer is in operation
Servo motor position once the timer completes the countdown

Instructions for use

The A button adds 12 minutes to the timer. An extra LED will light up for each press of the button. The B button decrements 12 buttons from the timer. An LED will turn off for each press of the button. The photograph below shows two lit LEDs on the microbit, indicating 24 minutes or less are left on the timer.

The two lit LEDs indicate that 24 minutes are left until the servo motor is activated

The last timer setting is recorded to the memory on the microbit. When the board is reset, it will start counting down from this time. So, if you set the timer to 2 hours (10 LEDs lit), on resetting, you will see 10 LEDs lit up and the board will take 2 hours to trigger the servo motor.

The reset button on the back of the board restarts the board. Please see the photograph below which shows the position of this button.

Underside of the microbit with the rest button indicated, next to the battery connector

Hardware description

The components of the system are shown in the picture below. On the left is a AAA battery pack containing 2 x AAA batteries. I use battery packs with a switch, which I get from eBay. The microbit is in the centre, slotted into a kitronik microbit edge connector. This edge connector allows the signal pins of the microbit to be connected to the servo motor using female to male jumper cables . The cables are designed for the 0.1" pins and sockets found on the edge connector and the cable connected to the servo motor.

AAA. battery pack, microbit, servo motor

The full assembly including cabling is shown in the photo below.

AAA battery pack (right), microbit and edge connector board (centre), servo motor (top), connectors (right)

A close up photo showing how the cables from the edge connector and the servo motor connector are connected is shown below. The black/brown wires are ground, the red wires are the battery voltage and the yellow wire is the PIN0 signal line.

Pins from cables connected to the Kitroniks edge connector on the left, sockets connected to the servo motor on the right

The photo below shows how the cables connect to the pins on the Kitronik edge connector.

Cables connected to the Kitronik edge connector. Yellow goes to 0, black to 0V, red to 3V.

BBC micro:bit wrist holders

With my handshake project, a microbit and AAA battery pack need to be worn on the wrist. They can be vigorously shaken. I don't want the equipment flying off! So what can I use that will hold the microbit and batteries safely in place and is comfortable and safe to wear?

I tried a couple of armband holders aimed at iPods recently. Both of them are suitable for housing a BBC microbit and a AAA battery pack. Prior to this, I used a wrist holder that I made myself.

The advantages of repurposing an iPod arm band holder instead of making one yourself are:

  • Saves you the time of making one.
  • The clear plastic cover makes it easy to clean.

Please find photographs of the armband holders I tried out as wrist holders containing a microbit and AAA battery holder below. First a top-tip!

Velcro tabs to secure armband straps

Whichever armband you re-purpose to be a wrist holder, as the wrist is narrower than your arm, the end of the strap will no longer stick down. The end will flap free. As this end of the strap has the hook velcro on it and the rest of the strap is the loop kind, the strap will no longer stick down to itself. You need to make some double sided hook velcro tabs. See the photo below.

Double sided hook velcro tabs

These are lengths of sticky back hook velcro, stuck back to back. Place them on the loop velcro to enable the strap to stick to itself when used on the wrist.

TuneBelt Armband for iPod touch 4G

The TuneBelt iPod touch 4G armband holder can be used to hold a microbit and AAA battery pack as shown in the photo below. Use some double sided velcro hook 'gender bender' strips to allow the strap to stick to itself when used on the wrist.

iPod touch 4G arm band in use as a microbit and AAA battery pack wrist holder
TuneBelt iPod touch 4G used as a microbit and AAA battery pack holder, front view

arm band in use as a microbit and AAA battery pack wrist holder

TuneBelt Sport Armband iPod touch 4G box
 

igagdgitz iPod classic armband holder

Larger than the iPod touch 4G holder. Costs about twice as much - about £10 from eBay. The build uses thicker neoprene. The rear panel folds down to allow easy installation and removal of the microbit and battery holder. This is made from a decent thickness of neoprene and is held securely in place with velcro on three sides.

The strap is longer and bulkier than the iPod 4G holder . If you know you are going to use this arm band as a wrist holder, it would be worth trimming the strap down. Then you would rely on the velcro double-sided tabs to stick the strap down unless you sewed some hook velcro on to replace the tab that you had cut off when shortening the strap.

iPod classic arm band in use as a microbit and AAA battery pack wrist holder
igadgitz iPod classic holder, front view, containing BBC microbit and AAA battery holder. There are two velcro tabs near the plastic to enable the strap to latch onto itself when worn on the wrist.

 
Rear view, showing fold down flap which allows acccess to the interior