These are some of the coolest circuits on the net. I can't wait to read the writeups on them!

the smd version for your day 21 flasher is here:

https://github.com/rodan/electronics/tree/master/forever%20blinker

youtube was inserting garbage in the URL, so I put it here too, just in case.

Alan congratulations on your excellent series of Advent circuits you must be burning a lot of midnight oil for the series and must be difficult with working etc but congatulations again.

Best Regards

Ian VK2IJ

Mark,

I got these from Rockby.

They are still fairly "peaky" around 2.7 kHz, but they work fairly well in general. They aren't the most efficient, but they make nice "clicks" for geiger projects and resonable sounders for things that don't matter too much.

Rockby carries a smaller black one which isn't too bad either. It has a higher Q and works great around 2.5 kHz for alarm applications.

You can always take them apart and use the element in your own horn, say made from cardboard, or in a pinch the top of a plastic drink bottle cut off (like a funnel) works quite well. Without the resonator in the piezo body they are more broadband, but still have mechanical resonances in the AF spectrum (and ultrasound region too).

Regards,

Alan

Arv,

Indeed, I have a *LOT* of writing up to do at some point...

At the moment just getting a non-trivial project out per day is taking up most of my free time. I'll probably start on the write-ups after everything has settled down over the Christmas break.

Regards,

Alan

Alan

Great idea for an advent calendar and great circuits. I like your work desk, I have a very similar looking one, covered in projects!!

Where do you get your piezo speakers from? I had given up on them as being useful for anything except alarm circuits some time ago. i must be using the wrong type!

Might be good if you provide info on how to calculate the current limiting resistance (Imax = 0.65 / R ) because many seem to have problem with this part of simple current limiters.

This circuit for current limiting can also be used in the charge leg of sweep oscillators to provide straight-line voltage ramp and thus a linear sweep.