[time-nuts] Odd request

[David Forbes]

Tom Van Baak (mobile) wrote:
> 
> But one easy way to do it today is start with a $5 standard
> quartz clock display. 1) Either run a precise synthesized
> 32 kHz signal into it (replacing the xtal), or drive the little
> bipolar stepper yourself.
> 
> A 50 millisecond +1.5 VDC pulse is all you need; next
> second give it a -1.5 VDC pulse, etc. This is a few lines
> of code for a microcontroller. I've got pictures of this
> somewhere on my web site, I think.
> 

Tom,

With all due respect to your love of software, a microcontroller is a 
bit of overkill for this application.

Use a 74HC74 D flip-flop connected as a divide-by-two toggle register: 
connect Q-not to the D input and feed the 1PPS into the C input; connect 
S and R to +5V.

The drive pulse to the coil is generated very simply with a capacitor 
(~0.1 uf?) in series with the clock solenoid. This will produce a 
positive pulse when the flip-flop flips and a negative pulse when it flops.

You don't need to worry about the 1.5V coil voltage rating - the 
capacitor will absorb the blow. I'd start out with a smaller capacitor 
(.001uf maybe) and increase it until it pulses reliably, then select 
perhaps twice that capacitance for reliability.