RPN-duino

[Chasfield]

I opted for the 0.96 inch display to keep costs down but a 1.3 inch one could used instead with only a couple of mm added to the length of the device. Here is a BoM summary. Items with specific costs are listed first in GBP inclusive of shipping. Following these come some rough cost estimates of quantities of commodities that I had on hand.

0.96 inch 128x64 OLED module £6.90
Arduino Nano compatible micro-controller £3.70
ECO 16250.06 4x4 keypad £6.00
5-way tactile switch – PCB mounted £3.50
Slide switch £0.50
AAA three cell battery holder £1.75
5x7cm solderable breadboard £2.00

Laminated label tape for key legends £5.00
2mm carbon fibre effect ABS sheet £1.00
3 mm acrylic sheet £1.00
Hardwood strip £1.00
Double sided sticky foam tabs £1.00
2.5 mm plated machine screws £1.00
Small countersunk wood screws £1.00
Two part quick setting epoxy £1.00
Solder £0.50
Self adhesive rubber feet £1.00

The total comes to £37.85.

The structure is formed from planes of 3mm acrylic sheet, spaced by hardwood strips. The open sides are infilled with strips of carbon fibre effect ABS sheet. The 5-way switch PCB and OLED display are mounted on a 5x7 cm piece of project breadboard, which has been sprayed matt black on the visible top side. The Arduino Nano is soldered directly onto the row and column header pins of the keypad. The latter module has a soft Casio type of action and is of screwed together construction. This made it easy to dismantle so that the keys could be re-orientated and resequenced. It was necessary to bring the row and column headers to the top edge. As shipped, they are set at the bottom and the device originally featured telephone style ordering of digits. Some brands of keypad are held together by heat stakes and are worth avoiding.