An Interesting Two-Transistor Relay Timer

I came across the printed circuit board for this circuit completely by accident. It looked like an interesting and clever little design, and I had more than enough suitable parts lying around in my component drawers, including a pile of spare relays. So I decided to build one and measure what it could actually do. … Read more

On the Teardown Bench: Radtel RT-470 – What’s Inside a Modern Handheld Radio?

This time, the device on the teardown bench is not broken. My Radtel RT-470 is fully functional and gets regular use; it simply needed a thorough cleaning. For that reason, I did not take it apart any further than what you can see in the photographs. Even so, there is plenty to discover about how … Read more

The Honeywell XC100D on the Dissection Table

A Honeywell XC100D carbon monoxide alarm that had reached the end of its service life recently came into my possession. At this stage, the unit may still appear to operate normally, but it can no longer be considered fully reliable. It signals this condition with a sharp chirp once every minute, accompanied by a flash … Read more