This page details a modification that turned a stand-alone timestamp into a simple homemade master clock capable of driving minute-impulse secondaries (without correction).
This started as a completely normal Acroprint Time Recorder model 125NR4 stand-alone synchronous dual-color manual-print timestamp found at a local yard sale. The stamp mechanism makes a really loud clicking noise every minute—just like impulse clocks (but louder)—so I decided some experimentation was in-order.
You are looking into the left side of the mechanism. The lever with the yellow plastic boot on the end advances the minutes (this is what you push to manually set the time). The microswitch directly underneath the lever is my addition. In operation, the cam on the motor shaft releases the lever abruptly causing the stamp mechanism to advance, which also releases the microswitch contact, allowing the impulse secondaries to advance simultaneously with the stamp.
This setup also allows the secondaries to advance while manually setting the stamp mechanism; but, with the microswitch installed, it is no longer possible to manually advance the mechanism more than one minute per stroke. As shown, the position of the microswitch can be adjusted somewhat easily, as it is only attached with double-sided tape and pressure from the faceplate against the red spacer (the microswitch and spacer are both parts from a scrapped Gra-Lab 165 timer, by the way, the base of my first homemade impulse driver). The microswitch is positioned so that the contacts close for a duration of about two seconds, but slightly more or less would be possible.
In practice, a power supply small enough to fit inside the timestamp case should probably be fitted and used to power the secondaries, but an external supply is used here, connected to a screw terminal block on the back.
There you have it—a functional minute-impulse system with a simple compact master clock built practically for free.
Of course, it also still works as a timestamp, as originally intended. (The stamp reads August 01 at 1:41am; the afternoon hours are instead underlined and dates don’t have leading zeros.)
other possible modifications
If I were going to actually use this setup, I would probably add a latching relay and a neon indicator lamp to warn of a power failure. It would be neat to wire the lamp to be on normally and position it to backlight the red acrylic trim piece directly above the stamp slot (but that would require some creative drilling and gluing).
Another interesting modification would be to drill the faceplate and attach a seconds bit to the end of the motor shaft, which would center somewhere between the numbers 9 and 10. (And I just might do that, since the faceplate was already scratched by bent hands under a previous owner.)
Of course, in the end, what I would really like to do is to simply make the timestamp a secondary instead of a master, but I have yet to come up with an appropriate solenoid for that. And I’m holding out for a real slave stamp…