Binary Clock skipping.

[diegotheslinger]

Hello.

I'm a first year EE student and i put together this clock from this schematic and website. **broken link removed**. It works by stepping down 60hz to 1 hz and using this as a time base for the seconds, min, and hour using 4-bit counters.

Now the problem that I am having, is that the clock seems to double its freq. and skip once a about 10 or more leds are lit at a time. Starts off fine, counting seconds but once it gets a few minutes lit, it starts counting at about 2hz.

Any hints at tracking down what it is? I ended up decoupling almost all of the IC's thinking it was that but no luck. Would exceeding the power output of the IC's cause it to skip? I have checked it over a few times and there doesn't seem to be any solder bridges or anything.

Any tips would be appreciated. I only have a multimeter with a freq. checker at my disposable to use for testing.

Thanks!

 

[audioguru]

The schematic has errors. It shows 74393 TTL counters that will not work but the parts list shows 74HC393 high speed Cmos counters that will work.
The 2N3906 PNP transistor is a nightmare. It should be a 2N4401 NPN transistor with a series base resistor.

 

[Diver300]

The transistor is only there to add 60 Hz flashing to all of the LEDs which is plain annoying. The resistors limit the LED current, and they can be changed to alter the brightness.

The text does mention the fact that there should be 10 nF capacitors between Vcc and ground on each IC.

 

[diegotheslinger]

I did not include the transistor when I built mine, and I am also using the 74HC393's. I'm thinking i'm going to just design one myself after this, but I would kinda like this one too work cause its already all put together and it seems like i'm close to getting it to work. I did end up putting some 10nf ish caps between Vcc and ground, but it didn't seem to help at all...

 

[diegotheslinger]

hmmmm wierd.. after about a month of it not working, I turned it on today and it works fine.