Minikeyboard, replacement of original Yaesu FH-2
The transceiver Yaesu FT2000 (as well as FT950 and FT450) supports 2 features: CW memory keyer and phone voice keyer. The keyers are operated from panel - small buttons in lower left corner. If you want to use that button often you soon find the buttons are too small, hard to access (mike connector obstructs), the horizontal pressing is not very ergonomic. Yaesu guys know that and therefore they offer a keyboard FH-2 that contains 12 buttons they guess the operator needs mostly. I don't know, but I feel I need ofter only 5 of them, to recall all 5 stored messages. The rest is not used too often, I can press the panel buttons instead. So I decided to construct an own keyboard - I have been inspired by article in Czech HAM magazine (by OK1UKV).
It is quite simple. There are just switches and resistors inside the box - the transceiver measures the resistance between signal wire and ground, different value means different button. You can find a list saying which value corresponds to which button in circuit diagram (including for buttons that I don't use). I haven't test how is the value critical - I just search thru my "resistor collection" and always found the two having resistance with less than 10 ohm difference while connected in series (but I think you can use less accurate resistance). To set the precise value using 2 resistors is much easier than to find one having exact value. The push switches are from "prehistoric" PC keyboard - the era before useless "rubber switches". But I am sure you find replacement easily.
There is nothing else to say....