Update! I fussed around in KiCad for a little while. This program takes some getting used to for sure.
Anyways, I made a schematic! I was wondering whether you guys could check my work and offer some advice.
It's slightly unfinished, first because there's certainly going to be some terribly incorrect things my very inexperienced self messed up, second because I couldn't find any footprints or symbols for an IN-14 Nixie for KiCad.
Here it is:
It's a lot to tackle so rather than just throwing it at you guys I'll explain my thought process with everything.
Oscillator CircuitThis is the section on the bottom.
- I took your guys's advice and used the CD4060 (thanks greenpossum and Gyro). I found a random schematic off Google Images (probably not a very good way to find a schematic, but it looked legit). I'm not entirely sure how the resistor values near the crystal were derived.
- The CD4060 divides the 32kHz signal down to 2Hz. The CD4027 takes that 2Hz signal and halves it to get that golden 1Hz.
- Looking on DigiKey, there seems to be an abundance of 32.768kHz crystals with a capacitance load of 12.5pF, I think I'll use one of these. So I would think I should use 25pF caps, but I looked at the CD4060 datasheet and there was an input capacitance listed. Should I take this into consideration when calculating these capacitance values? (I misread the datasheet as 5pF, it's actually 7.5pF so the caps should be only 10pF, that way the total capacitance would be 12.5pF.)
Should I throw in an adjustable cap?
Decade CounterThis is the middle part of the schematic. I did lots of crazy things here that I'm really not sure will work.
- The second digit of every section (
hours, minutes and
seconds) uses all digits zero through nine. When it counts past nine, it resets back to zero and then sends a clock signal to the next decade counter.
- The first digit of the
minutes and
seconds sections only use the digits zero through five. So, when these counters reach six, it has a wire running to it's reset pin to reset itself and it sends a signal to the next decade counter to increase by one.
- There's some funky stuff happening with the hours section. Here's why. I'm making a 12-Hour clock. Unlike the 24-hour clock, which goes from 0 to 23, the 12-hour clock starts at 1 and goes to 12 before turning back to 1. There's no such thing as "zero-o'clock" with 12-hour time. To tackle this issue, I just advanced the numbers by one. Let me explain.
With all the other CD4017 counters, Q0 controls the digit 0 for that Nixie Tube, Q1 controls digit 1, Q2 controls digit 2, and so on. But with U4 (the counter that controls the second digit in the hours), Q0 will actually control digit 1, Q1 controls 2, Q2 controls 3, etc.. and Q9 controls 0. This way, it starts out at one-o'clock and ends at twelve-o'clock.
- Once it reaches 12-o'clock I want the clock to reset. So, I made a simple AND gate with some NPN transistors. When the first hours digit is on 1 and the second hours digit turns to 3, it resets.
- I wanted to be able to adjust the time. So I added some things. First, I added a disable switch (SW3, underneath U14 on the far right). I want two things to happen when this switch is hit: 1) It stops the clock from counting up so I can adjust the time, and 2) It resets the seconds part to 00. I achieved this by sending the high voltage to the Enable pin of U14 and the Reset pin of both U14 and U12.
- To adjust time, I want to be able to press a button to increment the minutes or the hours by one. That's what SW1 and SW2 are for. I connected them to a little de-bouncer circuit using some resistors and capacitors, and added D2 and D3 to prevent the signal from being backfed to the previous counter's output.
Nixie DriversIt's the top section.
I'm hoping this part is self-explanatory. Each of those pins on the different ICs will go to one of the cathode digits of the nixie tubes. I'm using the little trick with the zener diode to clamp the voltage and keep the magic smoke inside the IC packages (thanks greenpossum and pqass!). I'm hoping it'll work out with just one zener for everything (thanks for the advice Tim!). And crap, looking at it I just realized I put the zener in backwards!! oops!
Each nixie will receive 170V through a 20K resistor on each anode. (Just had a thought. Will I need a high-voltage resistor?) I'll go ahead and use a power supply module. Thank you tkamiya and greenpossum for advising me with this
I need to figure out how to put Nixie tubes in KiCad. I think at this point I'm just about ready to start troubleshooting.
Please let me know what you think of this circuit and if you see any issues