This has been designed to enable the headrest of a wheelchair play either chords or percussion.
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Overview 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. Operation 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". Code 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. |  |
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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 |  |
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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. |  |
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Internal layout. |
| Front panel wired. |  |
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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. |
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The completed item
| Top Box Components | Supplier | Units |
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 |