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NSH Electronic Keyer / CPO

N. S. Harisankar / VU3NSH
Tel : +91 491 2576102, 9895741932

Specification and Features


  • 9V to 12 V - AC / DC input
  • Speed Control
  • Tone Control
  • Transistor Keying
  • Only 4 IC for Circuit
  • Built in input for CPO
  • Electronic Key or CPO selector
  • Side Tone on/off
  • LED - indication for Dot / Dash

This circuit is an Electronic Keyer built with 4 IC’s and it can be used as Code Practice Oscillator (CPO). The advantage of using an electronic key is dash : dot ratio is fixed (3:1), the characters are self completing, while using the paddle drive; no strain for your wrist. i.e., you can drive this key with your thump and index finger. So you can feel “iambic operation” (each characters, dot / dash, is completed even before the paddle released). One can send faster with proper spacing in CW work.

U1 NE555 is free running astable oscillator which is producing clock pulses. Clock speed can be adjusted by varying speed control 220K lin. Using J-K flip flop U2A & U2B HEF4027 and U3. the proper ratio 3:1 (dash : dot) is formed by this two JK flip flops and OR gate over the entire speed range. In addition, the characters are self completing which means that it is impossible to send another dot / dash before the pervious one is finished. The first JK produces dots and second JK produce a dash twice as long as the dot. The OR gate U3 combines a dash and a further dot to give a total dash length of three times to dot length. The output from U3 HEF 4071 (OR gate) feeds to solid state keying transistor T1 and side tone oscillator. U4 forming astable audio oscillator. Its frequency is 300 Hz to 3 KHz; which is selected by varying tone control (100K Lin).

Switch S2 is tone on/off switch. S1 is main on/off switch for this circuit. One can wish to use CPO mode by selecting CPO / EK switch to CPO and on S1; connect straight key (S-key) and practice CW. In this mode transistor keying is not possible. For electronic keyer mode; select CPO / EK to EK mode. Then press paddle to dash or dot, then control 220 K lin (speed control) for set word per minute. Set tone control 100 K lin for your favourable tone. If you do not wish to hear the side tone, then switch off S2. LED will indicate dot - dash characters. The vin is 12V - 500 mA AC or DC. IC7809 - U5 is the regulator for the circuit. You can download PCB artwork from this link.

Electronic key / CPO
Fig. 1. Electronic key / CPO schematic

Component list
Table. 1. Component list

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