Motor controller

Light-Controlled Pond Pump

This circuit was constructed to control the pump in a garden pond, so that it automatically turns on at dawn and off again at dusk. Not only does this mean that we don’t have to get cold and wet when turning the pump on or off manually but it’s also one less job for our kind neighbours when we go away on holidays! The controller is powered from the pump’s existing 25VAC mains transformer. A bridge rectifier (BR1) and 1000? F capacitor provide DC power to the circuit. For dependable operation, this is regulated to +12V by a 7812 regulator (REG1), while a red LED (LED1) provides power-on indication. The light sensor (LDR1) is a Cadmium-Sulphide photocell obtained from Tandy Electronics. The photocell forms a voltage divider with trimpot VR1.
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Author: Ian Hogan – Copyright: Silicon Chip Electronics
Source:http://www.extremecircuits.net/2010/06/light-controlled-pond-pump_18.html

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Simple dc motor speed controller using quad NOR gate

Here a quad NOR gate (IC1-CD4001) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from the multivibrator drives the base of Q1, which in turn drives Q2-MJE2955 and the motor. The motor’s mean supply voltage (integrated over a 50Hz period) is thus fully variable with VR1 but is applied in the form of high-energy “pulses” with peak values of about 12V.
this slightly more complicated circuit gives better low speed control and higher torque.
This type of circuit gives excellent full-range speed control and gives high motor torque, even at very low speeds. Its degree of speed self-regulation is proportional to the mean value of the applied voltage. Note that for most applications, the power transistor (Q2-MJE2955) in both circuits will need to be mounted on an appropriate heatsink.
Author: Ravi Sumithraarachchi – Copyright: Silicon Chip Electronics

Basic 12v Motor Speed Controllers using 2N3055

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first circuit shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of circuit gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second circuit uses a switchmode technique to vary motor speed.
a very simple motor speed controller based on a compound emitter follower (Q1 & Q2).

Source: http://www.extremecircuits.net/2010/06/two-basic-motor-speed-controllers_18.html