DC Motor Controller Circuit Using 741 Op-Amp

This DC motor controller circuit using a 741 operational amplifier operating as a voltage follower where its non inverting input is connected to the speed and rotation direction of a potentiometer VR1. When VR1 is at mid position, the op-amp output is near zero and both Q1 and Q2 is OFF.

When VR1 is turned towards the positive supply side, the output will go positive voltage and Q1 will supply the current to the motor and Q2 will be OFF. When VR1 is turned to the negative supply side, the op-amp output switches to the negative voltage and Q1 will turn OFF and Q2 ON which reverses the rotation of the motor's direction.

Skema Rangkaian DC Motor Controller Using 741 Op-Amp

741 Op-Amp Pinout

As the potentiometer VR1 is moved toward either end, the speed increases in whichever direction it is turning. The TIP3055 Q1 NPN power transistor has a collector current specs of 15A and VCE0 of 60V DC. The MJE34 Q2 PNP power transistor has a collector current specs of 10A and VCE0 of 40V DC.

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Rangkaian 3V FM Transmitter

This 3V FM transmitter is about the simplest and most basic transmitter to build and have a useful transmitting range. It is surprisingly powerful despite its small component count and 3V operating voltage. It will easily penetrate over three floors of an apartment building and go over 300 meters in the open air.

The circuit is basically a radio frequency (RF) oscillator that operates around 100 MHz. Audio picked up andamplified by the electret microphone is fed into the audio amplifier stage built around the first transistor. Output from the collector is fed into the base of the second transistor where it modulates the resonant frequency of the tank circuit (the 5 turn coil and the trimcap) by varying the junction capacitance of the transistor. Junction capacitance is a function of the potential difference applied to the base of the transistor. The tank circuit is connected in a Colpitts

Skema Rangkaian 3V FM transmitter

Place the transmitter about 10 feet from a FM radio. Set the radio to somewhere about 89 - 90 MHz. Walk back tothe FM transmitter and turn it on. Spread the winding of the coil apart by approximately 1mm from each other. No coilwinding should be touching another winding. Use a small screw driver to tune the trim cap. Remove the screwdriverfrom the trim screw after every adjustment so the LC circuit is not affected by stray capicitance. Or use a plasticscrewdriver. If you have difficulty finding the transmitting frequency then have a second person tune up and downthe FM dial after every adjustment. One full turn of the trim cap will cover its full range of capacitance from 6pF to 45pF. The normal FM band tunes in over about one tenth of the full range of the tuning cap.

So it is best to adjust it in steps of 5 to 10 degrees at each turn. So tuning takes a little patience but is not difficult. The reason that there must be at least 10 ft. separation between the radio and the FM transmitter is that the FM transmitter emits harmonics; it does not only emit on one frequency but on several different frequencies close to each other. You should have little difficulty in finding the Tx frequency when you follow this procedure.

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25V Capacitor Bank for OCL Amplifier

Rangkaian 25V Capacitor Bank

The circuit diagram below shows how the +25V DC and -25V DC are obtained. In order to provide power supply for stereo amplifiers, a power transformer rating of 80VA with 240V/36V centre tapped secondary winding is used. The secondary output of the transformer is rectified by using four 1N5401 diodes together with 4 electrolytic capacitors to smoothen the ripple voltage. A fuse and a varistor are connected at the primary input to protect the circuit against power surge. Here you can see the circuit’sdiagram diagram

Skeme Rangkaian 25V Capacitor Bank for OCL Amplifier

Although shown with 4,700uF filter capacitors, larger ones may be used. Anything beyond 10,000uF is too expensive, and will not improve performance to any worthwhile degree. Probably the best is to use two 4,700uF caps per side (four in all). This will actually work better than a single 10,000uF device, and will be cheaper as well.

It is essential that fuses are used for the power supply. While they will not stop the amp from failing (no fuse ever does), they will prevent catastrophic damage that would result from not protecting the circuit from over-current conditions.

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35W Audio Amplifier Circuit by STK082

Here is a 35W audio amplifier circuit built based on single Amplifier chip STK082. This is a very simple amplifier, very easy to build and produce sound output with a fairly large power of 35 watts into 8 Ohm loads.

Skema rangkaian STK082 - 35W audio Amplifier

This amplifier circuit is suitable for home power audio devices. The STK082 amplifier specifications might lead you to believe that it can use supply voltages of up to ±43V. but I don't recommend anything greater than ±25V if 8 ohm loads are expected, although ±30V will be fine if you can provide good heatsinking.

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Rangkaian Audio Surround Decoder

This circuit has been created to design a decoder circuit that will operate in a module that would produce an audio surround sound.

Skema Rangkaian Audio Surround sound Decoder

The operation of the above circuits starts as the stereo sound signal transports surround sound information on the master volume part of the circuit. This will drive the Left channel Lch attached to Model TL072 IC1A and IC1b in which Right channel Rch is attached. The outputs on these operational amplifiers would serve as the input buffer to the following stages of the circuit. IC2C is responsible for summing up the signals from the left and right channels that will power the central loudspeaker output while IC2D is responsible for increasing the phase difference between left and right channels which is encoded in the two channels and will be fed to the rear loudspeakers. It is necessary to ensure that the negative terminals between the rear speaker is not earthed because they will simply function in parallel with the main speakers.

The output of IC2D will power regulated delay unit of audio to the rear loudspeakers. This would lead to the creation of proper sense of spacing in accordance to the size of the room. This will incorporate op-amp sound delay signal IC5 MN3004 which has 512 stages. Since IC4 MN3101 is a clocking signal, it provides timing to IC5 as it functions as an oscillator in the circuit. Variable capacitor C17 regulates the delay time in the circuit. The presence of filters in the circuit is for the purpose of preventing noise that will be produced during the process. These filters can be regulated to cut the frequencies above 8 KHz and under 100 Hz, to be able to drive the rear speaker. The rear loudspeaker is small in size because its input is encoded with a bandwidth of 100 Hz up to 8 KHz. The filters are built around the IC6A/B which is also an output buffer. A potentiometer is placed in every output to aid in the adjustment and regulation of loudspeakers and amplifiers. The supplied power in the circuit is 15 V and every output can drive a single power amplifier.

List Compoment

R1-2-7-8-12-13-18-19-20 : 47Kohm
R3-4-5-6-21-22-34-35    : 10Kohm
R9-10-11-14-15-16-17    : 15Kohm
R23-24-25-33-36         : 100ohm
R26-27-28-31-32         : 100Kohm
R29-30                  : 5.6Kohm
C1-8                    : 47uF/25V
C2-7-9-14-23            : 47nF
C3-6                    : 1uF/100V
C4-5-10                 : 33pF
C11-12-15               : 10uF/25V
C13                     : 82nF
C16                     : 18pF
C17                     : 100pF mini adjustable capacitor
C18                     : 2.2nF
C19                     : 4.7uF/25V
C20                     : 100nF
C21                     : 10nF
C22                     : 180pF
C24                     : 150nF
RV1-RV2                 : 2 X 10Kohm  Log. pot.
RV3-4                   : 10K Log pot.
D1                      : 1N4148
IC1-6                   : TL072
IC2-3                   : TL074
IC4                     : MN3101
IC5                     : MN3004 

This Audio Surround Decoder circuit from www.circuit-projects.com

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Rangkaian Charger aki 6 Volt

Here is the circuit diagram of a low cost charger for 6 volt batteries. This circuit requires a regulated 10V-DC front end capable of supplying 2 Amps. Begins the charge period at 240mA and at full charge switches automatically to a float condition of 12mA. The capacitors should be the electrolytic 25V or greater.

Skema Rangkaian Charger aki 6 Volt

Switching transistor T1 is an TIP31C NPN transistor, Si-Power Output/SW, with a TO-220 case and can be changed by using a appropriate substitute such as the NTE291, ECG291, etc. Timer/Oscillator U1 is a 8-pin NE555V and can be changed with a NTE955M or ECG955M. Resistors R4, R5, R6, and R7 are 1% metal film types.

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