On 01/01/2012 12:23 PM, Tom Harris wrote: > I too have been mulling over a minimal GPSDO. > > Has anyone mentioned a PWM DAC? Even a "toy" microcontroller like the > Atmel AVRs can generate 16 bit resolution PWM, which sounds like it
.. > So a minimal GPSDO looks like a simple microcontroller (I would use > Arduino since we use these at work whenever we need to build something > in an afternoon) with a filter for a PWM DAC, so one opamp and a few > discretes. Of course as I write software for such beasts as a trade I > am giving the software a zero cost. > A 'bike light' sized microcontroller can do the job. Today I would have used something larger, and saved development time. On the other hand, having only room for 512 instructions prevented spending time on non-essential features. http://n1.taur.dk/simplexdo/ I used 8 bit PWM into a two-stage RC filter, making it easier to filter. To get 16 bit resolution I added delta-sigma modulation on top of the PWM. The ATTiny13 is not the right part for the job; It has no input capture. So space- and time consuming tricks are necessary to get cycle-accurate capture. Recently I discovered that some of the microcontrollers in the drawer would do nanosecond capture all on their own, but with a working tbolt, need has been lacking. /Kasper Pedersen _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
