DC Motor Speed Controller

This circuit takes benefit of the voltage drop across bridge rectifier diodes to provide a 5-position variable voltage supply to a DC fan or other small DC motor. It is not as environment friendly as a change-mode circuit but it has the advantages of simplicity and no swaping hash. The 4 full-wave bridges are linked so that every has two pairs of sequence diodes in parallel, giving a voltage drop of about 1.4V, relying on the burden present.

Circuit diagram:

DC Motor Speed Controller Circuit Diagram

The rotary swap should have \"make before break\" contacts which will have to be rated to take presents as a lot as about an amp or so. For better currents, better rated bridge rectifiers and a suitably rugged rotary swap (or solenoids) will most definitely be required. If you want to have smaller voltage steps, that you must use the commoned AC inputs on the bridge rectifiers to provide intermediate steps on the velocity swap.

Author: Stephen Butcher,

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Ultrasonic Radar Circuit

This circuit named ultrasonic radar, where this circuit can in applying at security system house and or other security and safety system. in principle this circuit consisted of transmitter and receiver which transmitter and receiver can work with the same frequency, if both having different frequency hence this circuit cannot work. For circuit transmitter is given in symbol T, which frequency yielded by two NAND gates, causing yields signal multi vibrator, this signal which will be sent by transmitter then bound signal from transmitter in comparing to signal which in yielding by receiver, at receiver in symbol R. which entering signal strengthened by TR3 and strengthened again by IC OP-Amp 741. The signal from Op-Amp then returned by IC 2 here signal compared to which then is sent to which NAND gate if happened difference of frequency hence will activate TR1 and TR2 for in attributing to siren or indicator lamp.

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How to Make an Accurate 7 Stage Op Amp Controlled Mains Voltage Stabilizer Circuit

In this article we discuss an interesting circuit which can be used  for controlling our mains AC line fluctuations and for producing very accurate stabilized voltage outputs for our domestic electrical appliances.

More innovative circuits HERE.

The circuit concept is rather very simple. It uses discrete op amps wired up as comparators to sense the voltage levels.



As can be seen in the diagram, each op amps inverting inputs are provided with sequentially incrementing voltage refrence levels through a series of presets which drops a certain amount of voltage across itself.

Each op amp compares this voltage with the common sample mains AC voltage level supplied to the op amps non inverting inputs.

As long as this sample voltage is below the refrence level the respective op amps keep their outputs low and the subsequent transistor relay stages remain inactive, however in case the voltage levels tends to shift from its normal range, the relevant relays trigger and toggle the transformer taps so that the output is appropriately equalized and corrected.

For example if the input AC voltage tends to fall, the upper relays may get triggered connecting the relevant higher voltage taps with the output and vice versa in case the voltage shoots upwards.

Here the op amp output inter-connections makes sure that only one optocoupler and therefore only one relay gets activated at a time.

Parts List

P1---P8 = 10 K Preset,

A1---A8 = IC 324 (2 Nos)

R1---R8 = 1 K,

All diodes = 1N4007,

All relays = 12 volts, 400 Ohms, SPDT,

Opto Couplers are all = MCT2E or equivalent,

Transformer = Pink Tap is normal voltage tap, the upper taps are in the decrementing order of 25 Volts, while the lower taps are in the incremental order of 25 volts.

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Auto gain Control op amp Circuit Diagram

An audio signal applied to VI is passed through the operational amplifier 741, U2. After being amplified, the output signal V2 is sampled and applied to a negative voltage doubler / rectifier circuit composed of diodes CRI and CR2, with the capacitor C1. The resulting negative voltage is used as a control voltage which is applied to the door] 2N5485 FET Q1. Capacitor C2 and resistor R2 form a filter for smoothing the voltage rectified audio control. The lFET is connected between pin 2 of the MC3340P grounded by a resistor of 1 kohm.

 Auto gain Control op-amp Circuit Diagram

As the voltage applied to the gate of FET] becomes more negative in magnitude, the channel resistance of FET] increases causing lFET to function as a voltage-controlled resistor. The MC3340P audio attenuator is the heart of the MCO. It is capable of 13 dB of gain or almost - 80 dB of attenuation as a function of external resistor placed between Pin 2 and ground. An increase in resistance decreases the gain from the MC3340P. The gain of the circuit is not entirely a linear function of the external resistance, but such behavior is similar across much of the gain / attenuation range. An input signal applied to the input of the AGC will cause the gate volt age the proportion lFET become negative. Accordingly, the JFET increases the resistance of the pin 2 to ground the MC3340P causing a reduction in gain. In this way, the AGC output is kept almost constant. source by next.gr

Datasheet file1: Click here to download LM741.pdf datasheet.Datasheet file2: Click here to download MC3340P.pdf datasheet.
Datasheet file3: Click here to download 2N5485.pdf datasheet.
Datasheet file4: Click here to download 1N270.pdf datasheet.

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