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Just wanted to share a possible paper silkscreen layout for the MIC5891 version "Big Clock" circuitry on a cheapie $4 Radio Shack 276-147 proto' board (11.4x16.0cm). I still have to place some components in the power supply section and I have to figure out where to place four diodes for the switch matrix. I wish I could get a little better spacing on the display too but all in all it doesn't look too bad.
Thats looking neat! A lot neater than mine, saying that I purposely put my LEDs and circuitry on separate boards so I could keep the footprint of the clock just a little bigger than the actual digits.
I also used Proto board, the kind with just little square copper pads, which I find easier to "blob" two together on than the Protos with the round pads, which makes joining the strings of LEDs easier.
I have now got the clock bug pretty bad and am just making the prototype segments for my next one with digits being about 10" high. Your suggested IC should be ideal for it as the segments only have 3 LEDs in them and draw 80mA at 12v. I just can't decide whether to go with Red, Blue or Green ones.
I had one mad scientist moment where I was considering RGB switchable segment colour but when I came to my senses and realised all the extra wiring involved I decided against it! hehehe
Anyway I can't wait to see the full design working with your IC and code so keep up the good work.
Edit. Here is a photo of one of my segments lit by white LEDs, its hard to get good shots of them with the camera, the spoon beside it is a teaspoon.
Sorry to ressurrect this thread but I have another related weird problem!
I have just made a second circuit the same as my first jumbo clock circuit the only difference being that I have replaced the small 2N3906 PNPs with larger TIP125 PNPs and neatened up the links a bit.
I always test points for correct voltage without the ICs in when building and all seemed ok, but when I actually tried the board I got something strange happening. All the segments are on constantly except the colon which is flashing happily as it should!
Now I just can't figure out what would put all the segments on but still flash the colon.
If I had burned another PIC and used new ICs all round then I would be suspicious of them but I have used the original clocks PIC and ICs, and they are fine when in the original board. I have put them back in the old one and it works happily.
So it must be the board but I have looked and looked but can't see the trouble. Can anyone suggest what to look at or test specifically for this strange problem?
Could substituting the larger transistors be a cause? BTW I have rejigged the board to accept the different pinouts of the transistors.
Some things I am sure about.
1) the micro is running - flashing colon shows this.
2) the LEDs are all fine - I'm testing the new board on the old LED setup.
3) all the ICs are ok - when in the old board
4) the power source is ok - same for both boards
The circuit is exactly the same as your design at the very bottom of page 5 of this thread. The same as the first one I made with the exception of the transistors which are a different pinout.
I have obviously made a mistake with the board somewhere, its just knowing what to look for.
The fact that the colon is working ok is really throwing me. Would the base resistors need to be different due to them being darlingtons?
hi Al,
The next step would be to replace the ULN and then check that the 0V pin on the ULN is connected to 0V.
After that check that the inputs to the ULN are less than 1Volt., lets know... we will solve it.
No answer to the Colon as yet, I am cogitating !
EDIT:
Looking at the circuit, the colon is fed by a resistor from +V, it shouldn't flash.???
I will try the ULN part as you suggested. As to the colon, mine gets its pos from the common anode of the minutes segments and has always flashed at 1Hz on the original and really still does on the new one honest.
Actually when converting my circuit from Jose's original one to yours I never noticed the colon mod on yours, as my display was already built, so it was kind of a happy accident that it flashes.
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