What I Have Learnt

My parts for my clock finally arrived on Monday, so I have been quite busy prototyping my base-15 design. From this, I have learnt/remembered a few things, and I would like to share them here:


1. TTL 555 timers' rise and fall times sometimes aren't fast enough for 74LS393s. It is best to put the output through a Schmitt Trigger (74LS14) first, so to clean up the edges.


2. 74LS393's reset is high when inactive. You need to ground this pin if you are planning on letting the counter reset itself


3. Some ICs don't like clamping circuits


4. RGB LEDs need to be diffused if you want to use a mixture of colours.


5. Staring directly at non-diffused LEDs hurts the eyes.


No doubt I will learn/remember more things as I go along, but this is just what I learnt in the past two days. Hopefully they'll be no more annoyances.

Base 15 Clock Design

My previous post outlined (sort of) my original idea for my digital clock. After practicing some woodwork, I realised that I am totally incapable of building what I wanted, so I decided to change my plans to work with my strengths, not my weaknesses. 

My "BCD" Design

So, a few minutes of pondering, I decided to make my own BCD display, but using symbols instead of numbers. After thinking some more, I decided that base 10 is boring, and base 15 would be a lot more interesting for time. 


I can already hear the cries of protest: Why base 15? Wouldn't 12 be better? Isn't base 12 awesome?


Well, when we think about minutes, the most commonly used times are quarter to, half-past, quarter past. These are all linked into fifteen minute intervals, hence base 15.


But, what would be an interesting way to show the most significant digit? Should I have unique symbols for them? No. How about colours?


That's right, each interval of 15 is represented in its own colour. Haven't decided which is which though, that is something I can play around with once my parts FINALLY arrive.

Base 15 symbols

I was originally going to work out 15 different "symbols" for 0 - 14, then work out the logic for it to work, but then I realised a quicker method. Hooking up each "panel" (each panel contains 3 LEDs) to a different output on the 74LS393 would generate symbols from 0 - 14 with little effort, and it would be very easy to implement.




Parts:
24 x RGB tri-colour LEDs (common anode)
12 x Dual colour LEDs (common anode)
1 x 74LS21
3 x 74LS393
5 x NPN transistors
3 x momentary on push buttons
1 x power button
1 x reset button
Various resistors
12 x 1000 uF capacitors
2 x 74LS08
1 x 5.1 V Zener Diode
1 x 9V battery