Fan Speed Controller Using Op Amp

We can make an enhancement to DAC drive fan controllers with the use of an external amplifier that closes the loop around the tachometer. Essentially linear control over the full range of 8 bit DAC codes from 0 to 255 is provided by this enhancement. This only requires a little signal conditioning and a suitable amplifier arrangement since the tachometer is already there. Figure a shows us that the tachometer pulses are conditioned such that all pulse width information is removed (differentiated) and only pulse rate information remains. Fan speed or frequency is represented by this pulses. Than, this pulse is used as the feedback to an integrating motor control amplifier.

To provide pulses just shorter than the duration of the shortest tachometer pulse at full fan speed, the time constant of the differentiator is initially set. Usually, this will provide a very little gain. We can increase the gain by decreasing the value of either R2 or C1. We have to set the gain so the fan just achieves full speed with the full DAC output applied to the input of the amplifier circuit.

To provide a smooth response to speed changes without any overshoot or hunting, the time constant of the integrator is set. Typically, this is done empirically with the actual system and fan. The response of the amplifier with the integration capacitor C2 at two values, 0.1uF and 1.0 uF is depicted by the plots in figure b and figure c. Either value meets the requirement for stability which dictates less than 25% overshoot

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Digital Fan Regulator Circuit Diagram

This is the project of Digital Fan Regulator Circuit diagram. The circuit presented here can be used to control the speed of fans using induction motor. The speed control is nonlinear, i.e. in steps. The current step number is displayed on a 7-segment display. Speed can be varied over a wide range because the circuit can alter the voltage applied to the fan motor from 130V to 230V RMS in a maximum of seven steps. The triac used in the final stage is fired at different angles to get different voltage outputs by applying short-dura-tion current pulses at its gate. For this pur-pose a UJT relax-ation oscillator is used that outputs sawtooth waveform. This waveform is coupled to the gate of the triac through an optocoupler (MOC3011) that has a triac driver output stage. Pedestal voltage control is used for varying the firing angle of the triac. The power supply for the relaxation oscillator is derived from the rectified mains via 10-kilo-ohm, 10W series dropping/limit-ing resistor R2.

Home automation with Telegram BOT

The project I’m going to describe today it’s a sort of proof of concept that will demonstrate the possibility to remote control sensors and actuators (for example a couple of relays) via Telegram. Telegram is an instant messaging application, similar to the famous Whatsapp. Last June, the Telegram developers announced that a new set of APIs were available to develop bots. [ ]

24 Hour Timer

Description: These two circuits are multi-range timers offering periods of up to 24 hours and beyond. Both are essentially the same. The main difference is that when the time runs out, Version 1 energizes the relay and Version 2 de-energizes it. The first uses less power while the timer is running; and the second uses less power after the timer stops. Pick the one that best suits your application. Notes: The Cmos 4060 is a 14 bit binary counter with a built in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11; and its frequency is set by R3, R4 & C3.The green Led flashes while the oscillator is running: and the IC counts the number of oscillations. Although it's a 14 bit counter, not all of the bits are accessible. Those that can be reached are shown on the drawing. By adjusting the frequency of the oscillator you can set the length of time it takes for any given output to go high. This output then switches the transistor; which in turn o

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