@Hop,
I wouldn't go the AC line way.
1. It is not accurate at all about ±5%
2. It is relatively expansive(transformer)
The way to go is with a CD4060 + 32.768kHz clock crystal (dirt cheap,and may be yanked out of a broken digital clock-almost all of them have one)
Ah, yes! I totally agree. The ubiquitous 32.768 kHz clock crystal used in millions (maybe even billions by now) of cheap wrist watches and battery powered wall clocks is the logical and best choice for creating a one-minute clock pulse with an appropriate divider. I should have suggested it. Thanks,
@dorke.
The transformer/diode/transistor circuit was a leftover from a problem I solved in the 1960s: how to trigger a pair of SCRs at the zero-crossing of the line voltage to minimize the RFI generated when switching on a large inductive load. In that particular instance a large solenoid actuated a heavy steel shutter. The device was already built and creating havoc with sensitive nearby data acquisition electronics. I was called in to "fix" it.
Today you can purchase off-the-shelf solid-state AC switches that delay turn-on until the next zero-crossing of the AC line. Almost all of them now have this zero-line-voltage-switching "feature" at no extra cost. I still use the circuit for bread-boarding because it is so simple and reliable. I usually connect the transistor collector output to a Schmitt trigger inverter to obtain a faster logic-compatible edge transition. In the original circuit, the transformer was connected through two current-limiting resistors to the bases of each of two NPN transistors whose collectors were tied together to a single pull-up resistor.
At that time I didn't worry about the reverse voltage being applied to the base-emitter junction of the transistor that wasn't conducting... an engineering decision that I got away with using 2N3904 transistors because they tolerate up to 6 VDC reverse bias. The voltage from center-tap to each end of the filament transformer winding is about 4.5 V peak. The width of the collector pulse is very narrow because of the gain of the transistor, so it served nicely as a zero-centered, transformer-coupled, trigger pulse for back-to-back connected SCRs. It would also work nicely for TRIACs but the system was already built and TRIACs were not a viable alternative. Ergo, shoehorn in a "fix" to trigger the existing SCRs.
I will leave it to someone else to detail the divider chain necessary to create a pulse once each minute while I wipe the egg off my face.