Memory Expander

I ran out of space on the front panel to add more memory buttons and frankly the tiny switches that I used are not the most user friendly. But there's lots of memory left in the Arduino to add memories and the top of the box is a great place for large push-buttons. To save lines on the Arduino and wiring, the memory switches are connected to an analog input on the Arduino. When the switches are open the line is pulled high. Each switch pulls the line low through a different value resistor so when the switch is pressed a different voltage is presented to the analog input.

This makes it easy to add more buttons, in theory, up to 1023. But that would take very accurate resistors and careful reading. The practical upper limit is probably 16 push-button switches using 1% resistors. With 1K of EEPROM, that would be 16 memories with 64 characters each.

The current sketch is written to support 4 memory switches and the 2 switches on the front of the keyer recall the same message as S1 and S2 on the memory expansion. The memory manager app also supports 4 memories so if you would like to add more you'll need to make changes to the sketch.

For this exercise I put four big blue push-button switches on the top of the box and connected them like this: