Clock Circuit Design

Posted on Feb 5, 2014

Your HVsupply will work, but for your own safety and to avoid accidental damage to your circuit if the event you need to troubleshoot with a scope, I strongly encourage the use of an isolation transformer on the 120VAC input. Just a little 1:1 transformer, 30VA is plenty. That`ll get your circuit ground isolated from AC Mains ground, saving you much potential misery later. 2) Polarity of HV / connection of transistors:

Clock Circuit Design
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unless I`ve totally lost my mind, I do nelieve your polarity is reversed. Nixies are common anode (positive common) and your whole HV side is designed as though they were common cathode (common negative). Since I have not yet looked up those CMOS part numbers and analyzed your logic, I`m not yet sure what Item (2) above is going to do to the logic design, e. g. will a second `stage` of transistors (or some inverter ICs) become necessary. As for the counting logic, I`m not willing to spend any more time on that until I see if you come back and post a response. No offense, but you are brand new here, lots of new people post once and never come back, and I don`t want to find out I`ve wasted my time. What I notice immediately about your counters is how you do your Carry/Reset. You need to re-evaluate how you are doing that on the ten`s digit of seconds and minutes because the way you have it now you will never see a "5" in those positions. Your hours look like they will count to 19 or 29 before resetting, probably not what you intended. Also your Time Set buttons are going to have unintended effect of resetting the counter "to the right" of the counter you`re trying to set. Diodes are needed. Edit to add: I would definitely assemble and debug that string of CD4017s on a breadboard before committing it to a PCB. As above, I find your Carry/Reset scheme dodgy and would want to prove out the design - using LEDs as needed to...

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