| Introduction |
This page contains two versions of the Accu-Keyer in CMOS. The first one was published in Electronics Australia. I browsed through many issues, but I have been unable to find the article or associate a name. This keyer used SN74C ICs rather than SN74 ICs (TTL). The SN74C ICs (CMOS) were Logic and Pin-for-Pin matches to the SN74 ICs (TTL). So, for the most part, conversion from TTL to CMOS was very straight forward. Although, some adjustments had to be made due to the high input and output impedances.
The second keyer was published in the August 1975 issue of 73 Magazine and was written by Gene Hinkle, WA5KPG. This was another conversion from TTL to CMOS except that the CD4000 series of CMOS was used. This meant that pin numbers changed and, in come cases, the logic was a bit different. For example, the CD4013 D-Type Flip-Flop, which replaces SN7474, has active High Set and Reset inputs. Whereas, the SN7474 has active Low Set and Reset inputs. Sometimes this is an easy adjustment, but other time the driving logic needs to be changed.
| Accu-Keyer (SN74C), Page 1 |
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Printable Images of each Schematic Page
- Page 1 - Keyer Timing
- Page 2 - Paddle Input and Dot/Dash Memory
- Page 3 - Output and Power/Ground
The original Accu-Keyer Clock Oscillator was said to start up irratically and often caused short elements (dots/dashes) at the beginning of a character. While I can not confirm this, the changes listed below for the oscillator are reasonable. The modifications help improve the startup and the extra inverter (U7C) reduces the loading on the oscillator and changes the trigger edge for the flip-flops, U4A and U5A.
Below is a list of changes.
- The oscillator transistors Q1 and Q2 were changed and the supply voltage to the oscillator was increased to 9 Volts.
- All 5 Volt power tieups on U4A, U4B, and U5A were changed to 9 Volts.
- The values of R1, R2, R3, R4, R6, C1, and C2 were changed.
- An inverter, U7C, was added to invert the clock signal going to the clock input of U4A and U5A. Originally, U7C was a spare gate.
- A 10KΩ pull-up resistor was added to U5B-13 (Reset).
- A Mono-Phone Jack (J1) for a straight key, a 10KΩ pull-up resistor (R15), and a KEY/TUNE switch (S2) was added to U7B-5, the KEY/TUNE input.
The original Accu-Keyer (TTL version) only showed the KEY/TUNE input as a PCB connection. The Phone Jack and KEY/TUNE switch in this version would have propably been added by a builder.
| Accu-Keyer (SN74C), Page 2 |
Below is a list of changes.
- At the Paddle inputs, a Stereo-Phone Jack (J2) for a Dual Paddle, a 10KΩ pull-up resistors (R16 and R17) were added to the keying input.
- The keying input resistors, R11 and R12 were changed from 150Ω to 1KΩ.
- The connection between U1C-8 and U3A-1 was broken and a 150Ω resistor (R18) and a 0.001 µF capacitor (C6) was added.
- All 5 Volt power tieups on U3A and U3B were changed to 9 Volts.
Like with Page 1, the original Accu-Keyer (TTL version) only showed the Paddle inputs as a PCB connection. The Stereo Phone Jack for Dual Paddle input would have propably been added by a builder.
| Accu-Keyer (SN74C), Page 3 |
This next drawing (Page 3) contains the Power Supply, Transmitter Keying, and Side-Tone Generator.
- The transmitter keying circuit was modified to drive a reed relay. This provided polarity insensitive output and the capability to switch up to 200V. While the reed relay does draw more current than the original circuit, the increased current consumption is more than offset by the savings of the modified sidetone circuit.
- The original Acc-Keyer did not have a Side Tone Oscillator. By itself, the NE555 would produce a pretty harsh tone. A small speaker output transformer transforms the speaker impedance so that the NE555 doesn't go into current limit, improving the sound and dramatically reducing the current consumption. This extends the life running on a 216 battery considerably. A coupling capacitor also improves the sound.
- The power wiring was simplified and changed so that the keyer runs from a 9 Volt battery. If there is a noise issue, additional 0.1 µF capacitors across the IC's power and ground, might be in order.
| QRP Accu-Keyer, Page 1 |
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Printable Images of each Schematic Page
- Page 1 - Keyer Timing
- Page 2 - Paddle Input and Dot/Dash Memory
- Page 3 - Output and Power/Ground
This section contains the QRP Accu-Keyer by Gene Hinkle, WA5KPG, which was published in the August 1975 issue of 73 Magazine. The QRP Accu-Keyer was an offshoot of the original Accu-Keyer, by James M. Garett, WB4VVF. The QRP Accu-Keyer uses much less power than the original Accu-Keyer, due to the use of CMOS (CD4000 series) integrated circuits. The QRP Accu-Keyer was aimed at the QRP crowd, but could be used by anyone. You just had to be careful, because CMOS was sensitive to external fields.
If you put this next drawing up against the original Accu-Keyer, you will see that they are almost exactly the same. The only noticable difference is the addition of U8-C and U8-D, which are used to invert the Initial Dash and Initial Dot signal. These were added because the Set (S) and Clear (R) inputs for the CD4013 Flip-Flops are Active High, as opposed to the original flip-flops used in the original Accu-Keyer. The CD4001 NOR Gates are used, as opposed to a CD4049 Hex Inverter, because they are left over from the oscillator on page 1.
| QRP Accu-Keyer, Page 2 |
This next drawing details the Power/Ground wiring for the integrated circuits. Generally, for a hand wired circuit, this is usually done first. As noted, I only show the keying arrangement from the original article. The author intended this design to key a HW-7. If you need a different arrangement for Grid-Block keying or Cathode Keying, almost any of the keying arrangements, from the other keyers, can be used.
| QRP Accu-Keyer, Page 3 |