Started 19th March 2018
I got fed up of turning on and off the fan that blows fumes away from me whilst soldering. An obvious idea is to detect when the soldering iron is out of its stand and turn the fan on, and turn it off when the iron is returned.
I found that I could detect the iron using a TCRT5000 "Reflective Optical Sensor with Transistor Output" - which consists of an infrared LED and a photo-transistor. If there is something close to the sensor then the infrared light is reflected and turns on the transistor. I have a clone Hakko 907/936 iron, and these have a large metalic nut at the top of the barrel which makes a good reflector.
The first set of photos shows modifying the iron stand to hold the sensor.
This consists of making a hole big enough for the TCRT5000 to see through, the sensor is then glued into a 3D printed part which in turn is glued to the soldering iron stand. All the 3D print and software code is available from the link below. I bent the legs on the TCRT to form two sets of pins which two 2 mm JST female connectors would fit on to. The wires from these go into a KF2510-4P female connector.
The other part of the project is an Arduino Pro Mini which monitors the sensor and turns the fan on and off. It lives in a 3D printed box which is attached to the back of the stand where there is usually a sponge in a metal tray. 12 V power comes into this box and a switched 12 V supply to the fan comes out. The Pro Mini runs from the 12 V. A large p-channel MOSFET switches the power and a small NPN transistor matches the 5 V Pro Mini voltage level to the 12 V. I used high side switching to keep all the exposed metal at zero volts.
Photo showing how the fasteners work, bottom bolt goes through the stand, box and board, all three are held together by the hex stand-off. Top bolt goes through the lid and into the stand-off.
Using a micro-controller might seem excessive, but as soon as I decided to improve performance by comparing the signal from the sensor with the LED turned on and off, it looked a good choice. There is a hole in one side of the box that the Pro Mini can be programmed through using the usual six pin header.