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.

Insurance

I can think of two songs that contain the word "insurance":

• "Desolation Row" by Bob Dylan
• "Love At The Five & Dime" by Nanci Griffith

But there must be more...