The Learning Circuit 18: DIY Desktop Fume Fan

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The Learning Circuit

sudo Sergeant

The Ben Heck Show

Solder fumes can be harmful to your health. Luckily, Karen has a solution. Build a desktop fan that keeps solder fumes away. You can salvage any old fan, as long as it’s DC, for this to work. To build this circuit, you’ll also need a nine volt battery or a twelve volt power supply, a power switch, an LED, and a resistor. You’ll need the resistor to power the LED, which means you’ll need to know the resistance value. Karen goes over calculating the resistance value to use either the 9 volt or the 12 volt power supply.

Karen's Toolkit:

Product Name	Part Link
PC fan, 12V DC 80mmx25mm	Buy NowBuy Now
Perfboard	Buy NowBuy Now
Board-To-Board Connector, 2.54 mm, 2 Contacts, Receptacle, 2212S Series, Through Hole, 1 Rows	Buy NowBuy Now
2x1 male header	Buy NowBuy Now
Toggle Switch, DPDT, Non Illuminated, On-On, Panel, 5 A	Buy NowBuy Now
LED, Red, Through Hole, 4mm, 20 mA, 2.1 V	Buy NowBuy Now
Rotary Potentiometer, 1 kohm, 200 mW, ± 20%	Buy NowBuy Now
2.1mm DC Power Connector, Jack	Buy NowBuy Now
AC/DC Power Supply, 12 V, 1 A	Buy NowBuy Now
Through Hole Resistor, 499 ohm, 250 mW, ± 1%	Buy NowBuy Now

The resistor will go in line with the LED. Since this fan is rated for a voltage equal to or higher than the supply voltage, I don’t need to add any more resistance. I also want to be able to control the speed of my fan. This would normally be done using a 555 timer or another chip using PWM. To keep the circuit simple, we’re going to use just a potentiometer instead. It’s not the most efficient way to build this circuit, but it works. Potentiometers are variable resistors. If put in line between the battery and the fan, by adjusting the resistance, we also adjust the amount of voltage supplied to the fan, making it go slower or faster. If we put the LED indicator in series with the motor and potentiometer, it would also be supplied a varying voltage, which would cause it to burn out. We don’t want that, so here’s what we’re going to do.We’ll use a DPDT switch which will put the fan and the LED in parallel. The switch will be supplied the 9 or 12V on both poles. The resistor and LED are in one circuit while the potentiometer and motor are in another, both placed after the switch. This way, when the switch is turned on, both circuits are supplied the 9 or 12V.