Arduino - controlling high voltage devices-from dc motors to ceiling fan speed controller

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Arduinos and raspberry pi's operate at a lower voltage (5v) and controlling led's, servos etc can be done this voltage or with a simple transistor based switching. In this post i will show different techniques used to control devices at a higher voltage and power levels. These techniques can be used in conjunction with many other projects for e.g remote controllers  to control high power devices like room heaters, lamps e.t.c In general, you need to couple the 5voltage control signals to the input of these switching circuits.

Safety Considerations

Some parts of these circuits operate at extremely lethal voltage and current levels. Do not attempt to work on these without understanding and following ALL of the relevant safety guidelines for high voltage and/or line connected electrical and electronic systems.

Controlling DC motors at 12 volt with Speed controle (PWM)

Controlling DC motors with PWM (pulse width modulation, to control the intensity/speed) is straight forward. Here we use a special transistor (TIP-122, datasheet) which is a darlington pair and can switch a device up to 100Volts (DC). It is a TO-220 package with all inside the package (see figure). Connect the PWM output (for speed control) to the base of TIP-122. Connect emitter pin to ground and collector pin to C fan/motor and the other end of fan to positive end of 12v DC.

Use any pwm pin (eg Pin 9 with analogWrite(9,speed_value);) and connect it to the base of the transistor (TIP-122) via 1k resistor

TIP-122 pin connection for controlling 12volt motor with arduino/raspberryp pi

Controlling AC lights, heaters, fans (120/220Volt)

There are two approaches. The simplest is to use a relay and this can be done with the same circuit shown above. The relay has a small electromagnet which switches on/off a high voltage line. Asecond approach which doesnt have any mechanical parts is a solid state relay (SSR). These devices have built in semiconductors which does the switching and there is an isolation in the form of opto-couplers  or so to isolate the low voltage arduino lines from the mains. These SSR can switch devices at 120 or 220 volts depending on the bulit and can be obtained from manufactures like omron also can be spotted on online stores like ebay.

Solid state relay to easily control ac 220v/120v devices with arduino

Controlling AC fan speeds with arduino/raspberry pi

It is normal to think that the pulse width modulation can be used to control the speed / brightness of ac devices by pwm ing the SSR. But it is not feasible and a different approach is needed to adjust the motor speeds in AC. The lights can be controlled by converting AC to DC as they works on both while AC motors need some tricks to adjust their speed. This is done by controlling the on time of triacs after a delay from zero crossing (more details on this is beyond the scope of this post). A manual control circuit for AC fan speed is shown below

AC 220v ceiling fan speed control with arduino pwm trick

But here is a trick with out the need for zero crossing and is borrowed from an article (dont remeber where) which used a similar approach on a drilling machine. See the modification above where a cds ldr is used in place of the variable resistor used to control the capacitors charging time and a pwm ed led is used to adjust the resistance value. This is a quick and dirty hack and may help some one. The correct way is complex and need to sense the zero crossing and the firing time of triac with respect to the ac cycles.