Top Box ~ for use with limited motor skills

This has been designed to enable the headrest of a wheelchair play either chords or percussion.

AMPs~Top Box



Portable unit offering 8 chords via 4 instruments. Additionally, 4 percussion sounds. The device is polyphonic.A "tone stretch" facility was devised during testing to give a more reliable output when the operation of buttons was less precise. Based on an Arduino UNO and a Sparkfun Music Shield. 3.5mm jack sockets are used to match the 3.5mm plugs on the Jelly Beans. RHS sockets ~ chords, LHS sockets ~ percussion.


The On/Off switch is on the rear panel, along with the volume control. One or more Jelly Buttons (large, low profile sensitive switch) are plugged into the 3.5mm jack sockets on the front panel . The switches are then brought in near contact with subject to encourage movemnt by triggering a sound. The top control changes instruments. The bottom control alters "sustain".


The device is powered by an Arduino micro-controller. Code :-Arduino listing in PDF form

The Development and Construction Process

Test software first, helps with weeding out bugs. AMPs ~ Top Box test rig
AMPs ~ Top Box ~marking up the socket holes Mark out and drill holes. Note the use of masking tape to stop the drill from skidding. Use a pilot drill first, or a dot punch. If using the latter, ensure the plate is fully supported or it could bend.
Use an undercoat formulated for aluminium before spraying on the top coat AMP ~ Top Box ~ Pianted front panel
AMPS ~ top Box ~ Arduino sheild stack The screw shield is in the middle to help locate any build faults.
Rotary switch used for instrument selection. It uses two digital inputs on the Arduino. This gives the sequence 00, 01, 10, 11. External "pull up " resistors have been added to ensure reliability. AMPS ~ Top Box ~ selection switch ~ binary selection
AMPs ~ Top Box ~ Internals ~ partially wired Internal layout.
Front panel wired. AMPs ~ Top Box ~ front pannel wired
AMPs ~ Top Box ~ Rear pannel Rear panel.

Top Box is fully polyphonic so multiple chords and percussion are possible. In use though it is only intended to use two inputs at a time. This is because the intention is to utilise a left and right head movement to trigger the "Jelly Bean" push buttons. To play (say) a C major or E major chords.

The tone-stretch gives between 0 sec to 2 sec delay when a triggered sound is released. Having (say) a 0.25 second delay is intended to reduce ambiguity in associating the sound with contact with a switch.

As an aside, I was adding the labeling when the outside temperature was around 90C in the UK with low humidity. The air was very static and the labels kept jumping all over the place.

AMPS ~ Top Box ~ Sound controls

The completed item

AMPS ~ Top Box assembled


Top Box Components Supplier
Unit Cost £'s
Total Cost
Arduino UNO Clone Hobby Components 1 £8.00 £8.00
Music Shield Sparkfun 1 £24.00 £24.00
Screw Shield 1 £6.00 £6.00
Amp Module Amazon 1 £2.75 £2.75
Visatron Speakers Kitronic 2 £7.00 £14.00
Speaker Grill Kitronic 2 £4.00 £8.00
3.5mm Jack Socket Mono CPC 12 £2.06 £24.72
Control Know Medium Maplin 1 £1.50 £1.50
Control Knob Small Maplin 1 £1.00 £1.00
On/Off switch Maplin 1 £1.00 £1.00
9v Battery Holder Amazon 1 £1.50 £1.50
LED CPC 1 £0.30 £0.30
LED Holder CPC 1 £0.60 £0.60
20k resistors Maplin 2 £0.30 £0.60
10 k resistor Maplin 1 £0.20 £0.20
10k Rotary Pot Maplin 1 £2.00 £2.00
Rotary switch Maplin 1 £1.85 £1.85
Misc Wire Maplin 1 £1.00 £1.00
Jelly Bean Switches 2 £30.00 £60.00
Case RS 1 £20.00 £20.00
Smaller Control Knob (Amp) CPC 1 £0.30 £0.30
Solder Maplin 1 £0.40 £0.40
5mm Brass nuts and bolts Maplin 8 £1.00 £8.00
    1 £0.00 £0.00
    46   £187.72