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Davac 5 is new design of voice/SSB keyer for Tucnak. Although version 5 may appear to be a successor to version 4, is not true. It brings some advantages but also lacks some features.

To choose the version that best suits your requirements, please look at the table:

Davac versions comparsion
Davac 5 Davac 4
Size small bigger
Drivers required No Yes
Isolated No, use the USB isolator Yes
Band output No Yes
USB Micro-B or A male B
Soundcard Is the soundcard itself Uses PC soundcard
Audio cables Shorter Longer
Modulation relay Solid SPST Mechanical SPDT
Separated grounds No Yes


Davac 5 inside box with cables
Recommended assembly is stencil, paste and reflow oven
Version 5.1 with optional USB-A


  • Simple assembly
  • All parts are SMD
  • Designed for SMD reflow
  • 3.5 jacks
  • 3D printed box
  • SMD LEDs + light guides on the top side
  • power supply from USB

Circuit diagram

Circuit diagram of Davac 5.1


  • R1, Y1, C2, C4 are not assembled in case of CM108B
  • Althrough preferred chip is the CM108B, is possible to assembly older CM108
  • The 93C46 is optional but recommended
  • The JP1 - Turns ON/OFF the audio mixer - please consult datasheet of the CM108B
  • I used LCBB-600 also instead of R9 and R16
  • R11 and R17 are for possible coarse attenuation

Connecting to the radio

  • MOD - Modulation output to the microphone input of radio
  • PTT - Push to talk output to switch Radio to the transmit (active low)
  • GND - One ground (ground plane on the bottom layer)
  • MIC - Modulation input from headset
  • BIAS - Microphone supply (from soundcard, not from radio)
  • CW - CW output to key to the radio
  • REC - Recording input to record band traffic

=Example for IC7400



  • PWR lights up - Device is powered from USB
  • PWR blinks - Soundcard is playing or recording
  • PTT - Push to talk is active (SSB and also CW)
  • CW - CW in the rhytm of Morse code
  • MIC - The SSR connects MIC to the MOD (off/disconnected if CQ is active)


  • CQ - Modulation level to the Transceiver
  • REC - Record level attenuator


Davac-5.1-gerber.zip Gerber files to order PCB at Elecrow or jlcpcb.com.


Davac-5.1-box.zip STL files for 3D printer.


  • Nozzle 0.4mm
  • No support, maybe brim in case of bad adhesion
  • Layer height - first 0.3mm, others 0.2mm
  • PETG or PLA

Light guides are made from transparent PETG filament.


Davac51-bom.csv Bill of material for tme.eu .

(not including cables)

Set USB string to EEPROM

Only if the 93C46 is installed. From menu Setup, CW keying, Davac5 options.

EEPROM edit in Tucnak

Post production inspection

Test points
  1. Connect device to computer. The green LED lights up.
  2. Start Tucnak. Go to CW keying, set Enable and Davac5.
  3. Go to Audio, Choose Davac 5.1 for playback and capture.
  4. Connect headphones to green jack (RADIO1). Run SSB CQ (You will hear it weak beacause impedance do not match headphones)
  5. Take multimeter, set it to diode measure with buzzer. Look at image above.
  6. Connect measuring needles to PTT points. Use TAB key in Tucnak to turn TX ON. The red LED lighs up and multimeter will beep.
  7. Press ESC to RX. Connect needles to SSBW points. Buzzer will beep together with yellow LED. Run SSB CQ (F5), LED and buzzer will OFF.
  8. During SSB CQ (or SSB recording) the green LED blinks.
  9. Press Alt+M for CW. Connect multimeer to CW points. Run CW CQ (F5). Multimeter will beep together with blue LED.
  10. Switch multimeter to Voltage measure to >3V range (4V, 20V...). Measure points BIAS. Voltage must be around 3V.