Assembling the Digi-Keyer

2023-02-15 | By Don Johanneck

Introduction

The advanced Digi-Keyer contains a treasure trove of electronic circuits that, when ‎interconnected, form a seemingly simple Morse code generator. Each circuit performs a key ‎task without the need for programming or microcontrollers. There is much to be learned from ‎building the keyer and exploring its various circuit functions.

Printed Circuit Boards (PCB)

Included in the list of available files are PCBs for the main board and the paddles as well as ‎detailed schematics for reference. Depending on which board house is preferred, gerber files ‎and the complete KiCad board file are available. The boards used in these instructions were ‎acquired through Digi-Keys DKRed PCB service.

Assembly

It works well to install devices from lowest to highest physical profile to prevent having to use ‎support materials and to prevent damage to the higher profile items. Using the BOM and the ‎references printed on the PCB, place and solder the resistors and capacitors; then install the ‎surface mount translator (U5) and USB Micro B connector (J3).

Assembled Digi-Keyer.

Next, install the ICs (U1 – U4), followed by the headers (J1 and J2). See figure 1. Leaving the ‎paddles for last, install and solder the remaining components. The paddles are press-fit and ‎require only enough solder to ensure electrical contact. However, soldering the entire paddle ‎tab is acceptable.

Using flux remover, clean up the front and back of the PCB until all residue is cleared away.

Using figure 2 as a reference, assemble the center contact by placing the contact washer on a screw, then slide on a small washer and secure it with the standoff. Try to keep the contact ‎washer centered as the standoff is tightened. It does not have to be perfect. Insert the ‎assembly into the PCB hole between the paddles and loosely secure it with a nut. Rotate the ‎contact until there is equal clearance between the assembly and both paddles, then tighten ‎the nut.

Center contact assembly.

Now add the two 3D printed adjustment cams by inserting a screw through the bottom side of ‎the PCB and into the cams securing them so they can still rotate but with considerable friction. ‎Rotating the cams reduces the gap between the inside of the paddles and the center contact ‎to increase keying sensitivity.

Cam and screw.

Place the PCB into the 3D printed base and secure it with screws. Add adhesive rubber feet to ‎the underside of the case to reduce movement while keying.

Adjusting and Testing

The keyer, as originally designed, is now ready to use. Insert a set of stereo headphones into ‎the “Phones” port. Pressing either paddle results in an LED flash and an audible tone on one ‎side of the headphones. The short tone is a DIT (or DOT), and the longer tone is a DAH (or ‎DASH). The length of the tones conforms to the Morse code standard. Once a paddle is ‎pressed, the keyer will not accept further presses until the last character is complete.

Adjusting the “Word Speed” potentiometer (R4) lengthens the tones and makes it easier for ‎beginners. The “Pitch Adjust” potentiometer (R21) allows the user to choose the preferred ‎audible tone.

Adding a Feather MCU and Display

For additional capability, insert an Adafruit Feather Huzzah32 microcontroller into the headers, ‎then insert an OLED display into the headers on the Feather. When programmed and powered ‎up, the display shows the DigiKey logo until either paddle is pressed. The display then shows ‎whether the press was a Morse DIT(*) or a DAH(-). If no other press is detected, the display ‎converts the Morse character to alphanumeric and displays the result. Following the rules of ‎Morse timing, words and sentences can be formed with the right combinations of paddle ‎presses.

Keyer with Feather and display

To practice with a friend, connect the link ports (J4) of two keyers using a male-male 1/8” ‎stereo patch cord. Your presses are heard in one ear while your partner’s presses are heard in ‎the other. Using different tones for each keyer helps to distinguish between users.

Test Points

Six test points and a test ground connection (J6) are located on the PCB. Using an oscilloscope ‎connected to a test point allows the user to visualize the signal passing through that point. Test ‎point 1 (TP1) is the Morse character square wave output of the flip-flop circuit. TP2 is the ‎negative square wave signal from the timing circuit that triggers the flip-flops. TP3 is the 555 ‎timer frequency reference/pitch adjustment signal. TP4-6 signals show the progression from ‎the 555 timer square wave output to the more desirable pseudo-sine wave that is sent to the ‎headphones.

Summary

Learning Morse code is challenging. The Digi-Keyer makes the job easier by standardizing the ‎DITs, DAHs, and spaces, which are critical to accurate communication. The addition of the ‎microcontroller and display enhances the learning process by showing the user the result of ‎their keying.

Resources

How Does the Digi-Keyer Work

Updating the Original Digi-Keyer

Creating Quasi-Sine from Square Waves

How JK Flip-Flops Work

What Are RC Timing Circuits

Interested in building the Digi-Keyer and learning how it works? DigiKey provides ‎the full set of plans, bill of materials, programming code, PCB files, and more in this repository:

https://media.digikey.com/pdf/Project%20Repository/Digikeyer.zip