Recently there has been a good discussion on how to monitor Soldering Irons and Stations. I was going to add this post on to the thread that was already in progress but since it was really a comment thread for someone else's build I decided to post this as a stand alone blog post.
I too have had problems in the past with a soldering iron at our business site. Since multiple people use the solder iron it seems that too often we were forgetting to turn it off and would come back to the shop after a weekend only to find it running. The last time it was left on it was my fault. Having chewed my son out many times before for his transgression it was his turn to let me have it. After enduring my deserved dressing down I went back to my home shop and designed a simple solution.
I put together a simple 555 powered monostable timer tied to a relay. It was my goal to have the timer run for 60 minutes and then shut off the solder iron that would be plugged into it. Due to the tolerance of the components that I used this actually turned out to be 68 minutes which was in the ballpark. The timer plugs into the 120VAC outlet in the shop and the solder iron plugs into the other side of the timer box. When the RESET button is pressed the timer turns on the iron for 68 minutes and then automatically turns it off. If one is still using the iron it is necessary to push the reset button for a second 68 minute period. This solution has proved very effective and the iron has not been left on since the timer was installed.
Here is a schematic of the Soldering Iron Timer
Correction to Schematic: There needs to be a 10 k resistor between the 12V rail and pin 2 of the 555 timer to work properly.
I wasn't too concerned with cosmetics for this project and so I built it into a used plastic box and labeled it.
John
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