PicoMite Memory Keyer

by Dave Benson, K1SWL


Assy & Setup Instructions (06-May)

PMK 2.01 Firmware 
(GNU Public License)


Parts List (PDF), or
Online via Mouser
(Order individual parts online or you can order all projects at once by clicking "Buy Project"!)

Purchase PCB

PMK Shields

Instructions (coming)

Shield Schematic

Parts List (coming)

Purchase Shield PCB







Have you ever had a simple project idea that becomes an all-consuming affair? It was worth it, though, and the results are exhilarating!

I had recently dabbled in one of the larger CW contests and I’m by no means a ‘Big Gun’ operator. I was making enough contacts, though, such that sending an exchange over and over became pretty tedious. I do have a modern rig that includes message recording from keyer paddles and subsequent playback. The issue? Two sequential button presses are required on a menu-driven display: the first to arm the message readout and the second to start the message. I found myself not pressing the first button firmly enough and instead of that CW message going out, I was altering the rig settings. I realize that there are a number of computer-based Morse applications out there. My shack is already extremely cramped for space and is located at the limits of Wi-fi coverage, so I needed a simpler memory keyer solution.

What to do? By way of explanation, I’m a diehard homebrew enthusiast and a frugal one at that. I don’t often spring for a commercial product if I can build one for myself, so a ‘D-I-Y’ Memory Keyer seemed like just the ticket as I cast about for a new project. The way forward was unclear, though. I’m conversant with C/C++ in the Arduino environment and it was time for a change.

I discovered that the Raspberry foundation recently announced an offering dubbed the Raspberry Pi ‘Pico’. Its tiny single-board computer module measures only 0.85 by 2.0 inches (2 x 5 cm) and has some really interesting features. Free software for this device includes the MMBASIC interpreter and there’s plenty of memory space. With the interpreter loaded, it’s referred to as the ‘PicoMite’. Best of all, Raspberry is selling the Pico module for only about $4. I was hooked right there!


PicoMite Memory Keyer (PMK)



(Download Schematic)



PMK Expansion Boards: "Shields"

"Shields" ... What a great way we have these days to extend a microcontroller board's capabilities and customize its features for a given application!  Such is the case we have provided for the K1SWL "PicoMite Memory Keyer".  The PMK already has a rich and flexible base hardware I/O -- meaning that it has pushbuttons, I/O jacks, LEDs, potentiometer, sound output and an incredibly powerful and inexpensive microcontroller that may be programmed using numerous languages to perform designated tasks.  Now we literally add on top of all this a "shield" expansion board to provide hardware to allow hams the ability to customize all this power for their own projects and applications.

At this time we have three Shields available for this customizable expansion to the K1SWL PMK platform:

Shield 1 is a bare prototyping board that plugs onto the PMK's Pico microcontroller and provides access to all its signals.  Design and solder your own circuits onto this open plugboard and bring your new application to life!

Shield 2 is a board that has three very popular hardware peripherals already "wired" on the pcb with software libraries available to run them: the popular 128x64 OLED display (16 text characters x 5 lines); an inexpensive GPS receiver board to provide accurate timekeeping and delivery of time-precision interrupts as-needed to the Pico; and the extremely popular Si5351 synthesizer clock board from QRP Labs, providing up to three RF frequencies for use in local oscillators, VFOs, and more.  Shield 2 is a very powerful plug-in to the K1SWL PMK.

Shield 3 is a two-part RF deck that serves (first) as a 40-meter QRP CW transceiver with the PMK serving as the keyer and radio controller.  The transmitter circuits are on the main shield pcb and the superhet receiver plugs on the shield atop three connectors around the edge.  (This shield is still in development but is expected to be ready for the FDIM Seminar and Dayton Hamvention in May.) 




PMK Shield 1: Prototyping Board


Provisions are made for adding an OLED display, a GPS receiver and the QRP Labs' Si5351 Synthesizer to the PMK for your custom hardware and software projects!  Plugs into the Raspberry Pi Pico processor on the PMK base board and provides full access to all the used/unused pins for an inexpensive-yet-powerful projects for radio projects.


Shield 2 Schematic


Pinheaders & receptacles for the Shields to mount on top the Pico controller


Purchase the PMK & Shields (bare PCBs-only)

(Please remember to select either US Shipping or DX shipping with your order below, as appropriate)

  K1SWL "PicoMite Memory Keyer" PCB ($5)
  Shield 1:  Prototyping PCB  ($3)
  Shield 2:  OLED-GPS-CLK PCB ($5)
  Shield 3:  Transceiver PCBs ($8)
Shield 3a = the OLED, GPS, Clk and Tx
  Shield 3b = the Rx
(Shield 3 pcb set Available end-May)
  Socket & Pinheader Set: for Pi Pico ($6)
Two 1x20 SIP socket strips for the PCB, 0.1" spacing
  Two 1x20 SIP pinheader strips for the Pico module, 0.1" spacing
  Socket Set for Shields ($3)
Two 1x20 SIP socket strips, 0.1" spacing
NOTE ==> Shipping to U.S. Destinations ($5)  
    Must select this shipping for US purchase
NOTE ==> Shipping to DX Destinations ($15)
    Must select this shipping for DX purchase


PayPal to: sales@MidnightDesignSolutions.com


Write check payable to "Midnight Design Solutions" and send to ...

Midnight Design Solutions
c/o George Heron N2APB
205 Okema Trace
Loudon, TN 37774


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