Sunday 26 September 2010

Beacon developments

The next step with the multi-mode beacon is a bespoke synth to replace the SDR Kits USB synth currently used.

I've decided to use the same Si570 chip used in the SDR Kits synth - which introduces the exciting prospect of homebrewing with surface mount devices!

Rather than make a whole board for the synth (thereby committing an expensive Si570 chip to single use), I've decided to make a small surface mount "carrier" for the Si570 and associated circuitry (3.3 V supply and level converters for the control signals) and arrange for this to plug into a larger "control board" using good old through-hole technology. This control board will drive the Si570, provide a "user interface" through an LCD display and some push-buttons and generally supervise operation of the entire beacon - hence the name "control".

Here's the board, mounted in the big box...

The main device is a PIC 16F872A - chosen because it has plenty of I/O pins and it was in the "junk box". The three holes near the crystal aren't a mistake - they're for a trimmer cap if I ever decide that this PIC needs to keep accurate track of the time. The Si570 carrier board will plug into the two four-pin sockets North-East of the PIC. You can also see the usual colourful parallel interface to the LCD, a multi-pin header to link to pushbuttons (etc), an in-circuit programming interface (I know I'm going to be re-programming this PIC!!) and a three-wire interface to the hi-rise controller board, through which the operating mode of the beacon can now be tracked.

Here's the display, proudly announcing the operating mode at the time of taking the photo...

I have actually made the carrier PCB - but not started populating it yet. Today is the morning after a particularly heavy "night before" and I didn't feel messing with microscopic surface mount devices would work as "hair of the dog" !

...-.- de m0xpd

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