The latest version of the DIN rail mounting zero-cross detector.

Note: 4n35SM optocoupler must be Vishay package option 7 (for required clearance).

AC input to monitor: 110/220VAC, <1A

DC input; 3.3/5VDC. Signal output will be the same voltage. Share ground with MCU.

Produces a square pulse on each zero crossing with a pulsewidth of ~1ms on a 50Hz supply.

Updates:

It's basically the same as the original circuit but with improved clearances. A particularly crucial one is the isolation gap between the mains side and the low voltage side, which must be min. 8mm. The standard 4N35SM optocoupler does not quite give enough clearance (only 7mm) so it needs to be package option 7 from Vishay which has slightly longer legs to give 8mm clearance.

I added test points after the rectifier.

To make it cheaper I went back to using separate diodes rather than a combined package for the bridge rectifier.

The board has square corners and no cutouts so should be easily panelized with v-cuts into panels of 5.

Enclosure: UM72 DIN rail PCB mount

https://www.aliexpress.com/item/32276247838.html

https://www.aliexpress.com/item/4000272944733.html

OR: Camdenboss CIME/M/SE1125SS (x2) + CIME/M/FE0000SS

https://www.camdenboss.com/camden-boss/cimemse1125ss-72mm-empty-modular-interface-support%2c-11.25mm-end-section/c-23/p-18376

https://www.camdenboss.com/camden-boss/cimemfe0000ss-72mm-empty-modular-interface-support%2c-foot-element/c-23/p-18372

DISCLAIMER: This project uses mains electricity which is HAZARDOUS and can cause ELECTRIC SHOCK or FIRE. This circuit must be independently reviewed, tested and certified by a qualified and registered professional before use. The author accepts no responsibility for accident, injury or loss resulting from the assembly and use of this project in any way. Provided for informational purposes only.