Kai has been loving the Kids Electronics Lab we made last weekend. Bea tells me he played with it all day on monday while I was at work. I’m happy that he likes it.

I have been pondering the best way to add some over-current protection to prevent damage to the batteries in the event of a short. A colleague suggested I try a Polyswitch - he even donated one for this project (thanks Ian!) thus saving me about $2.

This device is also known as a PTC fuse and is commonly used to protect loudspeakers. When a certain current is reached, it will trip and go into a high-resistance state until the current is removed. You can see a photo here of the device dropping the current to 120mA despite a dead short across the battery. The trip current is well over an amp so it does not affect normal operation of the board. Neat.