Noise problem I think

boards.

have just over half of the LEDs on at a time. If I

some are flashing, I get a few others near the ones

manor. I have tried slowing down the clock pulses

that has had no effect. I don't think it is the clock

flashing sequences going VERY fast with no problems. When

can send them. The scope meter tells me that with no

it was far less than 1 kHz, increasing the high and

have done extensive testing and debugging to confirm

between the pins are a lot shorter than the wires I

It could go away, but that would depend on your PCB layout. The same effects can be brought on by poor ground (and power) distribution.

happening when there are several (more than 32) 1s in a

You could add redundant ground wires and a gob of extra bypass capacitors to your proto board. Given your description, I would expect to see the threshold number of driven LEDs go up. If that happens, you will know "ground bounce" is hard at work bedeviling your circuit.

The solderless proto boards are often a waste of time. They induce or force poor layout, introduce a few pF between adjacent pins, and inevitably have excessive coupling due to all the air wires in proximity to each other. When I was starting my electronics education, it went faster once I realized that my proto boards should be shelved for use only in DC or near DC circuits.

As ICs have become faster, those proto boards have become all the more useless for the kinds of circuits that are interesting by being busy.

I don't have much in the way of capacitors around so I added 2, 2.2uFs that I had around, as close to the Vcc and GND pins on 2 of the 4 LED drivers as I could. That solved the problem, I could have almost all of the LEDs on and just a few flashing (so I could detect a errors) and didn't see any.

After that, it occurred to me to check the voltage drop from the PS. The prototype board for the RCM3100 has a 5V source I was using to power the LED drivers. After some testing I found that if I had more than about 6 LED's on at once, the voltage from the PS started dropping. By the time I had all the LEDs on the voltage was down to 4.8V and the regulator chip was starting to get fairly warm. So I disconnected the LED drivers from the prototype board of the RCM3100 and used a 4 cell NiCd pack to power the LED drivers and LEDs. With that set up even with out the capacitors it worked fine.

Makes for a good reminder why I never skimp when buying a power supply for my computer. A bad power supply, or one that just isn't regulating as well as it should, can cause all kind of random errors and it's one of the last things most people think to check.