PIC IAMBIC KEYER
Although still fun to build, the days of discrete IC electronic keyers are long gone. With the popularity of easily available cheap microcontollers, a multi-functional keyer is easily constructed. Compilers make writing firmware easier and testing is achieved by using PC-simulators and burning directly onto a flash rom version of the chip to make up a working prototype.
The circuit is a basic iambic keyer with one memory, allowing you to store a 'CQ CQ' message, for example. The original design was coded for a PIC 16C54 which has no EEPROM memory, so the memorised message was lost after power off. I modified the code slightly and used a PIC 16C84 which is easier to program by means of a simple serial interface. Modifying the code to make use of the 16C84's EEPROM memory should be possible, to prevent losing the pre-recorded message after switching off. The schematic shown is described in the source code but was changed slightly to simplify the recording/sending leds and switching - replacing these with a bicolour led and a three way switch respectively. If your rig doesn't provide a sidetone generator the RB6 'keyer out' pin from the PIC can be used to drive an audio oscillator. Mine was based around the popular 555 IC. Very simple and it provides volume and tone adjustment - see below.
The keyer was originally developed for the G-QRP Club,
featured in their 'SPRAT' journal and available as a kit, which included the
pre-programmed PIC microcontroller. A while back the code's author, Mick Hodges G4OPE,
released the source
code on the internet.
The iambic 'feel' is acceptable but not as good as my Super CMOS 3 Keyer. However, for a one chip effort and considering the code was released free of charge, Mick's done a fine job!
Other single chip keyers of interest include the K1EL-Keyer and the Tick-Keyer series. They have all the bells and whistles you would want also in a single chip ...but are commercial products. K1EL has recently made available the source code for his K8 keyer and this may be worth checking out.
NE555 Sidetone Generator:
This sidetone generator design was borrowed from the 'All-Solid-State Iambic Keyer' featured in an old copy of the ARRL Handbook.
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