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CW Keyer as a good microcontroller learning project

A keyer is just a step to more perfect code. That means less operator skill for better cw transmitter keying. A first step up from the simple straight key was the Vibroplex – “the brand of side-to-side mechanical, semi-automatic Morse key first manufactured and sold in 1905 by the Vibroplex Company, after its invention and patent by Horace Greeley Martin of New York City in 1904. [Wikipedia]“. That used mechanical oscillations to produce dots and dashes. The electronic age got going in WW II and an example of just how complicated a switch could be is described in February 1953 QST The Ultimatic – The key with a memory by W6SRY. It used three 12AU7 dual triode tubes and seven relays.

“The “Ultimatic” key [patent pending] considers interletter and interword spacings as specific code characters … The key combines a free running time base, a differentiating network, a dot generator, a dash generator, a dot memory, a dash memory, a sequencing circuit, a regulated power supply, a heavy iron base, and the front half of an old bug. Shoehorn it all into a 3x4x5 inch box and you have the Ultimatic, a key that gives Klein output from Lake Erie input. It does everything for the operator but spell and punctuate.”

And that’s supposed to be a good microcontroller starting and learning target?

Fast forward to September 1960 and K0MHU and The “Ultimatic” — transistorized in two parts. Alvin notes that he counted no less than 11 articles on automatice keys in QST between his article and 1953. “Considering the multitude of other subjects in ham radio, this indicates a high interest in a device than only helps you turn your transmitter on and off.”  He notes that the tube version “takes about a dozen or so watts … to operate a 20 mw relay” while his transistor verion only needs a couple of tenths of a watt. Alvin uses 17 transistors but seems a bit shy about the complexity of his circuit.

If you browse the DXZone section on Keyers, you’ll find all sorts of examples to examine. One reason for using the keyer as a starter project is that it illustrates just how much a microcontroller (mcu) can simplify the circuits. Compare The Iambic Keyer with Alvin’s circuit. Besides the power supply with a zener diode and capacitor and the transmitter keying circuit with one transistor, the circuit just uses several pull-up resistors and filter capacitors. By using an RC clock for the mcu as a speed control, EI9GQ simplifies the code so that, even in assembly, it is only a few lines.

There are not so simple keyers as well. Take a look at the feature list of, for example, the K1EL keyers. The K14 is an 8 pin IC that looks to be a Microchip PIC with the program embedded for $8. Art, K1BX, and Steve, K1EL have been making kits for quite a while as a part time business. One item they note in their feature list is the use of a keyer as a transmitting keying conditioner to take care of timing issues that may arise when using logging and decoding software on a modern PC.

The learning is not only about adding features, it is (or can be) about peripheral devices like using a PS/2 keyboard or other input, the intricacies of cw key timing, and the features built into modern mcu’s such as interupts, PWM, low power techniques, and interfacing. Then there’s the opportunity to learn about embedded software languages and mcu development environments.

A keyer built with an mcu can start simple and get as complex as you want to go. The simple means that both the circuit and the software are composed of only a small handful of parts or lines of code. The biggest issue is likely to be getting your code into the mcu unless you go for the PICAXE or other mcu that has a built in bootloader.

Another issue for the novice is the elmer — there is a lot of help ‘out there’ and some good models to show you what can be done and how it is done. That can make getting going and building a successful project much easier. 

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