CPU Board

Updated 11 May 2024 MW

The constructed CPU board. Note for bench testing a 2-Pin plug has been fitted in postilion C50 (Centre of the board) to supply 13.8V

Features in full

  • 1 x Raspberry Pi Pico.
  • 20 button Keypad (a sub board with 6-wire connection see below for picture)
  • TFT colour display that fits on the rear of this PCB.
  • Digital glue logic and radio function control interfaces.
  • The main Tuning combined Function Rotary control plugs in to the TUNE connector. This rotary control is a 400ppm device and has a lovely tune and spin action.
  • USB 4 port hub for interaction to a PC (etc) using USB (optional) for CAT control (CAT software to follow).
  • Plug in USB sound card for audio input and output (Optional)
  • A sturdy USB-Up USB-B connection to a desktop / laptop and fits on the rear panel
  • Spare USB connections
The CPU / Display board. May 2024


Build time: CPU Board less than 1 hour, Keypad Board less than 1 hour

Read ALL of the construction notes carefully before proceeding to get a good understanding.

Construction and mounting of the KeyPad

  • All resistors and capacitors are SMD and mounted
  • Mount and solder the 20 push buttons. They fit on the REVERSE side of the PCB. Be especially careful to ensure they are mounted completely flat against the surface of the PCB and solder two opposite of the 4 connections, and check again they are completely flat. Next colder the other two of the four connections. If they are not flat they will interfere with the holes in the Front Panel. If there is any tiny interference you can carefully file the side of any particular hole with a needle file.
  • Use some 6-core 0.05″ ribbon cable, roughly 80mm (?check) long. fir a 6 pin socket one end. Strip, twist and tin the 6 cores on the other end and colder directly to the KeyPad pcb so the cable comes away facing away from the buttons. Be careful to observe the orientation of the connector that Pin 1 on both ends aligns with Pin 1 on the other end. This socket fits into J7 (KEYPAD) on the CPU Board.
  • Mount three 0805 size SMD LEDs. Green for RX, Yellow for TX and Red for OnAir is suggested. The -ve, or Cathode end has to be on the GND (Ground-plane) end. See picture below.

CPU Board Construction

  • 320 x 240 3.2″ COLOUR TFT display is now the only display option. It uses the ILI9341 MCU. If you are not using the HamPiRadio front panel / case you can of course use other size TFT displays than 3.2″ as long as it is 320 x 240 bits and uses that MCU. Also check the connector. If wanted the TFT display does not necessarily have to be mounted onto the CPU, it can be connected using a ribbon cable.
  • Most parts are SMD and come already fitted.
  • Fitting hand mounted parts: I always fit High parts and electrolytic caps last, as they are easy to burn with the side of a soldering iron.
  • The Raspberry Pi Pico and the TFT Display are mounted into socket strips which are 8mm high. (See pictures). The TFT socket strip is on the REAR of the board.
  • When all the parts are fitted to the top of the board, the TFT can be plugged into the back, and two 10mm spacers and nylon screws and nuts used to mount it to the CPU board (?re-check). Just use the two mounting holes furthest away from the connector for this. (The other holes are not needed, and the TFT holes are very close to the glass, and not worth using).
  • Next the CPU Board can be mounted to the front panel. This is done with 4 x M3.
  • At this time there is no bezel for the TFT. (Needed: A contributor to design a bezel. I note JLCPCB are now doing 3-D printing…)
  • Other parts to be mounted are:
    • 5W 16V Zener diode. This is to safeguard against any spikes coming in the 13.8V supply line. I have seen a couple of these diodes go short-circuit meaning they have protested everything else.
    • 100uH Choke. The value is not so important but the current handling is more important. Use a ????? choke.
    • Fit the 16, 20 1nd 26 pin IDE Headers for the connection to the BPL, PA and Radio Boards. Carefully observe orientation.
    • Fit Pin Header connectors. Carefully observe orientation. If you have no intention of using a PC for remount sound, CAT control or Waterfall then the USB Hum is not needed so J1, 3, 4, 5, 6 do not need to be fitted. For firmware programming of the Pi Pico a USB can be directly connected.
    • Fir C50 1000uF, at lease 25V Wkg recommended.

Front Panel

  • The Keypad and CPU can now be mounted to the Front Panel:
  • First mount three LED Lenses for RX, TX and OnAir in the 3 holes.
  • For the Front Panel you can use whatever M# screws you like. Both black painted flat-head Pozidriv and Hex Drive screws look good.
  • The keypad then mounts to the Front Panel using 4 x M3 screws with 2 nuts on each screw. One nut each side of the PCB.
  • Mount the CPU Board to the Front Panel using 4 x M3 screws with ??mm spacers in-between.
  • Next the Tune/Function rotary control. Use ??mm M3 screws. Do not use longer ones or damage can be caused inside the device. Note there are 6 threaded holes in the Rotary Control and three holes in the Front Panel. By turning the Rotary Control body then three of the holes will line up with the Front Panel holes, but only three of the six.
  • Plug everything up. The Pi Pico connects to the USB Hub, any of J1, 3, 5 or 6 USB-Down connections. The USB to USB-B Panel mounting cable connects to J4 only (Or any USB Cable to a PC that works for you. This is the USB-UP connector. There is a red LED D5 near the USB Hub IC U3 that lights when a PC USB is connected. The PC should also give an audible USB Connected sound.

Programming and Powering up

  • Before powering up the board Program the Pi Pico firmware. This can be done with the PI Pico plugged into the CPU Bard or not.
  • Find the firmware here: https://github.com/HamPiRadio/HamPiRadio/wiki HamPi_Pi_Pico_Iss1_2_PCB_TFT_v17.ino.zip
  • Using the UF2 file is V17 of the HamPiRadio firmware CPU Board. Processor = standard Raspberry Pi Pico. A new feature is for the VFO Si5351 output current 2, 4, 6 or 8mA select-able per band, and also as a hidden menu feature for testing at each of these levels. To program 1. Unzip the following to see UF2 file. 2. Transfer it to the Pi Pico by switching it on (plug in the USB cable to a PC) with button pressed, then drag and drop the UF2 file to Pi pico as you would a memory stick in Explorer. It will program itself, delete the file and auto-reset.
  • The CPU Board is normally powered up through the 20 way Ribbon cable from the PA Board. For bench testing however you can supply 12 or 13.8V to the board between pins 1, 2, 3, 4 for +ve and pins 23, 24, 25, 26 for -ve. (Solder wires carefully across the back of the connector).
  • Switch on and the TFT should display information and the RX led should be on. Push-buttons should work and Tune should change the frequency.
  • All functionality might not work as yet as there is no Radio Board connected. This can be done when with a 26 way ribbon cable. The Radio Board is powered through this cable.

Any errors found or improvement suggestions please email them in, appreciated.

Keypad PCB. 3 x SMD LEDS are mounted on the rear for RX, TX and OnAir