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Today we got a surprise parcel from Germany. An enveloppe just containing a circuit board and nothing else, no name, no clue, no nothing...

Today we got a surprise parcel from Germany. An enveloppe containing only a circuit board and nothing else, no name, no clue, no nothing... Nice surprise! Thank you, we like surprises. So we connected a 9V battery to it and pushed the button. What would happen?

It started to make noise, like birds just out of their egg. The sound was a little bit loud and annoying, so we removed the battery to shut it off but, surprise!, it didn't! Is it a practical joke circuit? The reason it continues sqeaking for quite a while is the big electrolityc capacitor.

We made a video of it.



Really nice project, thank you for sending us this project. Perhaps you can let us know who you are? Someone from Germany apparently, in the neighbourhood of Mönchengladbach (according to the stamp)?