I started working on a schematic for the 555 looping circuit, and I ended up doing a PCB for it as well. You can download the files here. My plan was to hopefully etch and test out the board today, but those plans got delayed. I’ll probably give that a shot tomorrow. I’ve gone ahead and uploaded the PCB files I’ve been working on. It’s only at v0.5 till I test the board out. I’m also going to play around with the silk screen, but the layout probably won’t change, as I can’t see anywhere to reduce it further and still keep it single sided.
The PCB measures 1″ x 0.7″ and is single sided to allow for home fabbing. I could make this smaller with SMD parts, but it wouldn’t be single sided any longer. One position on each pot isn’t used, but I left them in there, as they could be used for strain relief instead. The diode is completely optional, as that causes the 555′s duty cycle to stop being 50%.
What that means, is that sometimes you want to press a button for a very short burst between longer pauses. Or have the button press for a long time between short pauses. Sometimes it doesn’t really matter, and you just want a square wave. In any case, you can change the configuration with this design. The diode also runs through a switch position, so that you can have an external control for it.
I also left a spot for an external trigger. That would allow you to hook this up to some kind of external circuit, like a sequencer or midi board. You’ll need to cut a trace for that, and the trigger voltage will have to be at least the same as the reference (which is currently tied to VCC). The trace you’ll cut is the one from TR to the 10uF cap. I’ll probably do a run of these if it works out, in which case I’ll make the side that needs to be cut.
I’m currently using two 100k pots to modulate the time. R2 is actually the left one (I should probably label them), and R1 is the right pot. If you want a simple oscillator, then just use a standard 10k resistor for R1. You can change both pots as well. Larger pots will give you slower rates, and smaller pots will give you quicker rates. You can also change out the 10uF cap to change timing as well. These are the values I found good for triggering simple toys.
I also did a quick PNG file for etching. You can either get it from Flickr, or from the PCB files. It’s high res, but should only be 1″ x 0.7″. If it isn’t then you’ll need to re-size it as well. The file has been mirrored, so this is actually the bottom layer as etched from a single sided PCB. Please let me know how yours turns out and what you do with it.