[time-nuts] TIC model

Bob Stewart bob at evoria.net
Fri Feb 14 22:45:58 EST 2014


Tom tried to steer me to the PICTIC recently, and I sort of brushed him off, because, quite frankly I didn't understand.  Now that I've really looked at it, it's a much better idea than using a dsPIC33 and brute-forcing it.  But, I don't really need everything the PICTIC offers so I started doing surgery, and this is what I've come up with.  

The nsVolts would feed one of the 10-bit ADC channels of the 18F2220 on the VE2ZAZ board, and the 1PPS signal does the obvious.  I had no idea what to use for the RC, so I used smaller and smaller values till LTSpiceIV showed a large range over 360 degrees of phase.  I realize that's probably a bad idea, but I have no point of reference, nor do I probably need the accuracy that would otherwise imply.  

The 1PPS input passes through the enabled tri-state buffers U2A and U2C to charge the cap until the Q output from the D-flop is sent high from the 10MHz signal and disables U2C.  When the 1PPS goes low, the cap is discharged and the D-FLop is reset.  In practice, the chips would be 74AC types.  I could only find LTSpiceIV models for 74HCT chips.  LTSpice says it's workable, but in practice, I don't know.  It might be finicky or unstable.  Any comments would be welcome.

http://www.evoria.net/AE6RV/TIC/TIC.png

Bob - AE6RV


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