Simple 4 Channel Commutator Circuit

This is design circuit for commutator circuit. This circuit is simplest form. The circuit is built by four FET that can be use for 4 channels. This is the figure of the circuit;

To reach low channel ON resistance (<30 Ohm) and low OFF current leakage, 4-channel commutator uses the 2N4091. The DM7800 voltage translator is a monolithic device. This devices give us +10V to -20V gate drive to the JFETs while at the same time giving DTL-TTL logic compatibility.

Simple Analog Multiplier Circuit

This is a circuit for a simple embodiment of the analog multiplier. This circuit provides three quadrant analog multiplication which is relatively temperature insensitive and which is not subject to the bias current errors which is plague most multipliers and circumvents many of the problems associated with the log-antilog circuit. This is the figure of the circuit;

By considering A2 as a controlled gain amplifier, amplifying V2, whose gain is dependent on the ratio of the resistance of PC2 to R5 and by considering A1 as a control amplifier which establishes the resistance of PC2 as function of V1, circuit operation may be used. It is seen that Vout is a function of both V1 and V2 in that way. Drive for the lamp L1 is provided by the control amplifier(A1). L1 is driven by A1 until the current to the summing junction from the negative supply through PC1 is equal to the current to the summing junction from V1 through R1 when an input voltage (V1) is present. This forces the resistance of PC1 to a value proportional to R1 and the ratio of V1 to V- since the negative supply voltage is fixed. L1 also illuminates PC2 and causes PC2 to have a resistance equal to PC1 if the photoconductors are matched. The controlled amplifier (A2) behaves as an inverting amplifier whose gain is equal to the ratio of the resistance of PC2 to R5. Vout becomes simply the product of V1 and V2 if R5 is chosen equal to the product of R1 and V-. To provide any required output scale factor, R5 may be scaled in powers of ten.

Since the T.C. of resistance is related to resistance match for cells of the same geometry, PC1 and PC2 should be matched for best tracking over temperature. Varying the value of R5 as a scale factor adjustment is used to compensate small mismatches. The photoconductive cells should receive equal illumination from L1, a convenient method is to mount the lamp midway between them. Controlled spacing and a thermal bridge between the two cells to reduce differences in cell temperature is provided by this mounting method. To the use of FET’s or other devices to meet special resistance or environment requirements, we can extend this technique.

An inverting output whose magnitude is equal to one-tenth the product of the two analog inputs is given on this circuit. Positive value is restricted for input V1 but V2 may assume both positive and negative value. By the lamp time constant, his circuit is restricted to low frequency operation. To minimize errors due to input offset current as outlined in the section describing the photocell amplifier, R2 and R4 are chosen. To reduce in-rush current when firdt turning on the lamp (L1), R3 is included.

[Circuit source: National Semiconductor Notes]

Simple Loud Hailer Circuit

This is a simple and useful circuit project of loud hailer the circuit uses only one transistor connected with transformer which puts out a loud sound. The circuit can be easily fixed in a metal package with the speaker mounted on the top. Heat sink is essential for the transistor or it will burn out, fix the circuit in metal package and also use this metal package as heat sink of transistor. This is the figure of the circuit;

Use carbon mic or telephone mic/telephone transmitter element. The circuit can be build inside of a speaker trumpet like the loudhailers available in market. Make sure that the mic is isolated from the speaker to prevent feedback. Use the transformer which will able to provide 5 watt output power.

Simple DC Motor PWM Speed Control Circuit

This is a circuit for DC motor circuit. This circuit is used PWM speed control using 555 timer IC. This is the figure of the circuit;

The 555 Ic is wired as an astable and the frequency is constant and independent of the duty cycle, as the total resistance (R charge + R discharge, notice the diode) is constant and equal to 22Kohm (givin a frequency of about 1Khz, notice the hum). When the potentiometer is all up, the Rcharge resistance is 1,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 21 Kohm, giving a 5% on duty cycle and a 1Khz frequency.

When the potentiomenter is all down, the Rcharge resistance is 21,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 1 Kohm, giving a 95% on duty cycle and a 1Khz frequency. When the potentiometer is at 50% , the Rcharge resistance is 11,0 Kohm (the diode prevents the capacitor to charge through the second potentiometer section and the other 1,0 Kohm resistor) , and Rdischarge is 11 Kohm, giving a 50% on duty cycle and a 1Khz frequency. The 555 provide good current capability to drive the mosfet fast and to drive a bipolar transistor.

Wireless Telephone Line Spy Circuit

Here’s a design of a phone bug circuit. This wireless telephone line spy circuit can be used to transmit the phone conversation to a nearby FM radio. This circuit must connected to a normal phone line. This is the figure of the circuit;

The first transistor is turned off, if the voltage drops to less than 15v (if the telephone line is in use). It will enable the second transistor to oscillate at approx 100MHz. Then transmit the phone conversation to a nearby FM radio.

Simple Proportional-Integral Motor Speed Control

This is a design of frequency-to-voltage converter application similar with RPM/Speed Indication is motor speed control. Here the converter is used to measure the actual speed which will be fed back to keep the actual speed stabilized according to a reference. This is the figure of the circuit;

If the speed is to high, the output of the F/V converter will reduce the drive power delivered to the motor, and vice versa. The resistor across the output and the inverting input determine the proportional gain, and the capacitor determine the integral gain. This negative feedback mechanism is the core of this proportional motor speed control system. [System's block diagram source: Microchip Application Note]