Miscellaneous Circuits

These are some miscellaneous circuits that I've decided to post here, for no real reason. Some things to keep in mind:

Most of these circuits have been on the door to my room at one time or another.
Most of these were put together, not designed per se. They worked for me, but I didn't do any timing analysis or anthing like that, so they might not work for you.
There is no documentation, but you should be able to figure out what stuff does.
These were built with parts that I happened to have, so I have done some heinous things, such as using LM339 comparators where a ULN2003 would have been appropriate. I've also mix-and-matched TTL and CMOS logic levels, which may be a bad thing, although I believe it's OK with the chips that I used. And I drive LEDs directly from TTL and CMOS logic-level outputs, which is also a big no-no.
If you blow yourself up, it's not my fault. No warranty, no guarantee, no free tropical fish.
Unless otherwise specified, V_cc is 5V DC. All of these, unless otherwise specified, have been powered successfully off of a USB port, which provides 5V DC with 500mA max current.
Unless otherwise specified, everything is otherwise specified. Including this.
If a value for a component isn't specified, it's probably not too critical, and you can probably figure it out. Transistors that aren't labeled are 2N2222-ish (NPN) or 2N3096-ish (PNP).

[top] Christmas Blinky Thing

This was my attempt to design a festive holiday decoration by replicating the "chasing" effect used by Christmas lights, which works like this:

1	2	3	4
on
on	on
	on
	on	on
		on
		on	on
			on
on			on

Unfortunately, I only used four LEDs, so it was decidedly un-festive, but they were red and green!

Later I used this to build an actual string of 16 LED christmas lights, using LEDs I had lying around, for mod 8.

gschem 4.46KB postscript.gz PDF 13.2KB

[top] Back and forth light doodad

Blinks seven lights back and forth. Pretty simple. This can get annoying...my neighbor got drunk one night and ripped this one off the wall. Can't say I blame him.

gschem 4.92KB postscript.gz PDF 14.3KB

[top] The Octometer

Counts to eight. More precisely, it displays "01234567" on a series of LED displays. Can be set to display "09876543" instead. Can also display "12345670", "23456701", "34567012", etc. by being put into the right mode and then poked in the right way. Could help with chem 1a, I guess, although all your answers would be off by one. Will not display "98765430" or anything like that. Also has an adjustment knob (yes, a knob!) to make it count to any n ≤ 7.

gschem 20.7KB postscript.gz PDF 39.8KB

[top] Message Thingy

This displays a message fed into it by a computer or other demonic contraption. Note that there is now a (mostly) better version here.

Has a bit-synchronous serial interface using a standard PC parallel port (because I didn't want to deal with RS232 level shifting or asynchronicity). No memory, so it must be fed stuff constantly. Also, since it displays in real time, you need a computer that's either pretty fast or dedicated to the job (but not necessarily both). Here's the C program that I used to drive the thing, which demonstrates my extremely helpful commenting style. (I'm better now, I promise :-)) I don't remember how exactly it works.

Basically, I believe it is something like this: You set the STROBE line high. Then you write out a bit on D0. Then you set the STROBE line low. When you've shifted out a whole screenful, you reset the display (STROBE high, D1 high, STROBE low). You should probably stick some delays in there somewhere, and I might have high and low mixed up for STROBE. There is a helpful feature that can display the message backwards.

Note that the Protel version of the schematic specifies 1N4735 6.2V zener diodes for D1 and D2. This is not correct, although 6.2V is high enough that it works anyway. A switching diode like the 1N4148 is better. I don't have access to a copy of Protel any more, or I'd fix the schematic.

protel 3 21.9KB postscript.gz PDF 25.4KB

[top] Traffic Light

Really simple. This is a 3-way (red/yellow/green) "traffic light" sort of thing that was used as an indicator on a door to a closet. Green meant you could go in; red meant somebody was in there. Nobody ever figured out what yellow meant. The only thing that makes this at all exciting is that it uses no transistors or funny three-position switches, just a center-off DPDT switch and a relay (because that's what I had at the time), and only allows one light to be on at once. This is mostly posted here for my own use, because I can never remember how I did that.

PNG 28.98KB