[time-nuts] GPS Talking Clock

Bob kb8tq kb8tq at n1k.org
Sun Feb 18 09:04:04 EST 2018


> On Feb 17, 2018, at 11:01 PM, Nick Sayer via time-nuts <time-nuts at febo.com> wrote:
> It’s been a while since I’ve posted here, but I’ve had a bunch of irons in the fire. I’m working on adapting my GPSDO to the ECS ECOC-2522, which the manufacturer claims has a short term ADEV in the low -12s, but I haven’t gotten it doing that well yet.

At least on this data sheet: 

https://www.ecsxtal.com/store/pdf/ECOC-2522.pdf <https://www.ecsxtal.com/store/pdf/ECOC-2522.pdf>

They don’t say much of anything at all about ADEV. OCXO’s in the little packages are rarely super stars when it comes to ADEV.


> But one thing that is ready (well, electronically it is - I’m still working on the laser cut case for it) is my GPS Talking Clock.
> The story is that I called the USNO time number at midnight on New Year’s Day, but the wife noted that it was the wrong time zone. That got me thinking, and I wound up designing a GPS driven simulacrum.
> It’s an ATXmega32E5 with the usual Venus838 timing module and a µSD card slot. The card is loaded with audio samples that the 32E5 plays back through its DAC. I got double-buffered DMA to work to feed the DAC, so audio playback is a largely background task. I just have to fill the buffer with the next block from the file every ~30 ms or so. The ticks and beeps are generated from an on board 1 kHz source and are turned on by a PPS ISR, so they’re as accurate as possible. The whole thing is basically as accurate as an aural clock can be - the latency induced by the speed of sound has far more impact than anything else.
> While the audio is turned off, the clock can also do Westminster Quarters (or any other chime you wish to load in).
> The µSD card is FAT formatted and the audio sample files are easy to make with ‘sox’ (raw, 1 channel, 8 kHz, 16 bit little-endian, unsigned), so there’s no reason you can’t substitute my voice with your own, or make your own chimes.
> It’s available at https://www.tindie.com/products/nsayer/gps-talking-clock/
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