Hardware

You only need a few components to build this keyer. They can be found on Ebay.com for below 10$.

If you only use it together with your radio you do not need the speaker transistor etc. 

The stm32f103c8t6 board also called bluepill.

Buy it here  https://www.ebay.com/itm/STM32F103C8T6-ARM-STM32-Minimum-System-Development-Board-Module-For-Arduino/233028113080

Then you need a programmer for the board, which are a ST-Link V2

Buy it here https://www.ebay.com/itm/Mini-ST-Link-V2-Stlink-Emulator-Downloader-Programming-STM8-STM32-w-Metal-Shell/152484956321

then you need some female jack for keyer and your radio. I found some on Ebay which are very inexpensive and do fit into a veroboard.

you only need 2 pcs.

Buy them here https://www.ebay.com/itm/10X-3-Pin-PCB-Mount-Female-3-5mm-Stereo-Jack-Socket-Connector-Pip-HFCA/264294048387

You can use some money on female pinheaders but it is not needed.

Buy them here https://www.ebay.com/itm/Pin-Header-Strip-1-27-2-0-2-54mm-4-50pin-Single-Double-Row-Straight-Male-Female/302851353108

Then you need

For the paddle input 2 pcs capasistor on each 10n

For the keying output for your radio you need 1 pcs100 ohm resistor, 1 pcs 2n2222 , 1 pcs capasistor 10n.

If you want to have a speaker on the keyer you will need 2pcs 100 ohm resistor, 1 pcs 2n2222 and a 10uF cap

Here you see my version with the little tiny board below the stm32 board.