After posting about my Syncal display project I was asked if there was space in the radio for the Arduino board:

There isn’t, but fortunately it doesn’t need to be installed into the radio.  The board is to make it easy to develop projects and also program the microprocessor chip.  The chip is the socketed DIP below the green LED.  The rest of the board is for power supplies, USB interface etc.

So what will happen is that I will get the code working then take the CPU chip out and mount it on a small perfboard with RC (no need for crystal accuracy in this application).  It will run right off the radio +5 volt logic supply.  This goes right between the OLED graphic display and the existing display board.

Then I buy another Atmega 328P chip to put on the development board for my next project.  Of course, I could be lazy and load my completed program onto one of these:

https://www.adafruit.com/products/2590

That’s a surface mount version which is 0.7″ x 1.7″ and only 0.2″ thick.  Then there’s only the need for 5 wires to the radio and 5 wires to the graphic display, no discretes.