blinkenlights

I made yet another blinky-light circuit

This one has 16 LEDs in a row. They all turn on in sequence, then they all turn off. Very simple.

It's a bit of a random design because of the parts I had at hand. In particular I didn't have any shift registers so I used 74574 8-bit D flip-flops.

The only part that I think was a little bit clever is the initialization circuit. When the device is powered up something has to feed the shift register zeros (or ones) for a while, until all 16 bits are cleared. This is just a comparator with an RC delay, but we want the capacitor to discharge quickly when the power is turned off. When the power is turned off, C2 discharges through D2 and the power supply load. Note that the delay could have been a lot quicker if I had tied the comparator output to the tri-state enable pins of the '574s rather than the input of the shift register. I think I was afraid that the LEDs and resistors in series wouldn't be good enough pull-downs for the inputs. Anyway, this design is vaguely robust against an LED becoming disconnected.

Silencing the Silent Spinner

The Silent Spinner is an exercise wheel that has a fancy ball bearing thingy that keeps it from sqeaking all night. (By the way, what's up with exercise wheels? Why do rodents voluntarily use a device that seems like something from the Spanish Inquisition? All night? In my room?)

After a year or so, though, my Silent Spinner (well, my mice's Silent Spinner, really) was starting to rattle. I figured the bearing was just cheaply made, but it turns out the problem was actually the way the two plastic pieces of the wheel snap together. I generally take them apart to clean and then snap them back together; turns out that a year of doing this has made them fit together rather loosely.

My solution was to stick a little piece of cardboard into one of the clips that holds the two halves together, like this:


I got the cardboard from one of the toilet paper tubes that I give them to play with, chew on, and browse the internet with. I'll have to change it when I clean the wheel, but at least my spinner is once again silent.