First second assembly is working, IC’s are 4017 decade counters

Clock with Second and Minutes assembly, working so far. Switches at the bottom of the picture are 20s transient display on, display on off and display bright/dim

Detail of hours module. 24 hours are reset with output from 2 and 4 to 2N222 NPN transistors

Seconds and minutes assembly are same hours have 0,1,2 hours. These pressed paper PCB’s are cheap and cheerful, but I wouldn’t use them in my next projects.

Hour assembly finished, all been tested and working, Notice how lean the bread board look 🙂
I have to work on Motherboard and alarm.

Finished Assembly:
Tubes, relays, display transient

Assembly to finish:

Motherboard assembly is finished
Switches inputs for resting seconds, master reset.
Setting minutes and hours
LED for pulse indication and switch pulse hold
Pulse input / output (with DPDT relay, NC for internal, NO for external) External pulse will be used for GPS disciplined oscillator or OCXO
with LM7805 +5V regulator, I have added a heat sink

Motherboard assembly – bottom side

Alarm assembly with LM386 mono amplifier module – £1 on ebay
4 inputs from minutes and hours
+5V,GND input
Alarm ON/OFF switch
Alarm Silent / Loud switch switching 555 timers and LM386 amp module
Alarm ON LED
Alarm flashing LED operated by 2N222 NPN transistor

Alarm runs for one minute or as long as all 4 inputs are in high state, signal runs via rotary selectors from decade counters. Output from rotary selectors triggers 74LS21N AND gate IC. First 555 IC switches on off in intervals and second 555 IC generating square wave signal, this is running to LM386 amplifier via 103 cap to filter DC to 3″ speaker on side if the chassis.

Alarm assembly – bottom side

All assembly modules are finished and working, time to start working on enclosure.

Relay Assembly change to vertical position to further reduce depth of the enclosure from 42 to 32 cm (4″ less)
This also reduce construction complexity as I would have to put them on 100mm posts, wiring to Nixie tube assembly wasn’t long enough. I use 12V / 30W LED switch mode PSU for the clock, this is more than enough even for powering clock + OCXO or the Rubidium frequency standard should this be required in the future. Total consumption is about 10W with Bright tube display setting.

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