Author Topic: Compact variant of SM1000 digital voice adaptor for use inside equipment  (Read 133 times)

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Offline richard.cs

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  • Electronics engineer from Southampton, UK.
    • Random stuff I've built (mostly non-electronic and fairly dated).
I've been working on a simplified, more compact, version of the SM1000 FreeDV Adaptor. For those who don't know it's a small box that translates between analogue voice and baseband digital modulation. It uses the codec2 audio codec, current firmware supports the most common 1600 bps mode, with a possible update in the future supporting a 700 bps mode. The hardware is an open design (TAPR), detailed here: designed by Rick Barnich KA8BMA and David Rowe VK5DGR.

Basically my intention was to strip out the isolated interfaces and the power supply, and compress it down to a dual-in-line module that can more easily be built into other equipment.

The schematic of a standard SM1000 is here: and the whole device is around 80 by 100 by mm. I've turned it into a square PCB 30 mm on a side, with two 12-pin headers. The intention is to run the same firmware and to that end no microcontroller pins have been remapped or functionality changed. I've attached my schematics and a few pretty pictures of the layout. I'm intending to release this under the same license, but if no-one else is interested I'll just make up a couple for myself.

1) If anyone who is interested could take the time to review the schematic against the SM1000 and spot any sillies that would be much appreciated, thanks.
Edit: one error found so far, thanks Steve. I screwed up some pinning where my symbol differs from the eagle one.

2) Bare PCBs are looking to be about £2 (China prices), and the total BOM about £15. Does anyone want any boards? If so I'm happy to combine with my order.

The board is 4 layer, 6/6 track and gap, 12 thou minimum drill. It's just over 30 mm square. The original design was Eagle but I've done mine in Altium because that's what I am familiar with. Passives are all 0603 plus a couple of larger capacitors. I've tried to break as many spare microcontroller pins out to testpoints as I could.
« Last Edit: February 12, 2019, 11:30:24 pm by richard.cs »
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