开云体育

Hey guys. It's been a while! I had a summer class which was taking up all my time. Now I have about a week before Fall classes. So in the meantime!

I'm coming very close to finishing the circuit for my clock. I finally got to programming my PIC16F876. I then realized that there is no internal clock. woops! I think I'm going to go with this:

Anyways. Onto my question. I have currently set up a prototype for my circuit. The difference being I'm using 7SEG displays instead of my tubes. I plan a sort of modular approach to testing my circuit. I already tested the power supply and tubes. Now I just need to make debug the functionality of the software and such, using the 7 segment displays. It's hard to test a temporary setup with the tubes because of the pins on a Z573M.

I plan on using a 1x6 multiplexed circuit. I'm not worried about it being possible because I know it's been done. Here are my questions:
1. I want to get a better idea of what timing is involved. I want to ensure there is no ghosting. I plan on having a dimming option if it is viable. It may already be so faint once multiplexed that it doesn't make sense. I assume the mux is as simple as: - set 74141 with A - turn on A - wait - turn off A - set 74141 with B - turn on B - wait - turn off B... etc. It's the wait that I need some direction towards.
2. When I was playing around earlier with a single digit on my arduino and noticed that when it was multiplexed I could see it pulsating. Can I find some frequency where I won't notice this?

Thanks!
-Mike

490-1208-ND is a 4MHz ceramic resonator. For clock accuracy its pure crap. That parts has 0.5% accuracy. That's 5000ppm, or ~7minutes / day off. A regular crystal has accuracy of 30ppm, or ~15minutes / year (~3 seconds / day). Amazingly, the US and Western Europe, have AC line frequency, that if used, will keep your clock ON time, within a minute, per year (2ppm).

Muxing is commonly used for displays, including nixies. Nixies do have a finite turn-ON time. They don't turn ON instantly. Typically, its in the range of 10's of microseconds. As for muxing frequency, try a complete set faster than 60Hz, to avoid flicker. That is: Dig-1 On for 2.5mS (milliseconds, or 2500microseconds), then blank (all digits off) for 200uS (microseconds), dig-2 on for 2.5, blank (200uS), and so on, for all 6 digits for (2.5+0.2)=2.7mS*6=16.2mS (or 61.7Hz). During those blanking intervals is when you switch the digit data going to your ONE (common) 74141.

Thanks threeneurons. I hadn't thought about the accuracy issue. I am using GPS to set the time which also increases every second. But I still need accuracy in case it's not connected. It's probably best I go back to finding a good cap/crystal combo instead of a resonator.

Thanks for the info on the muxing. That's a huge help.