Simple Power Battery Tester Circuit

This is a simple design circuit for battery tester circuit. In this circuit, operating will controlled by transistor 2N3904. This is the figure of the circuit;

In the circuit, LED will turn on if the voltages is over 42V. Threshold will increase about 1 V per 1 kilo ohm increase in R2. The current drain is about 7 mA with button pressed.

[Circuit schematic source: Hobby Projects Application Notes]

Simple pH-Electrode Circuit

A pH electrode measures hydrogen ion (H+) activity and produces an electrical potential or voltage. The operation of the pH electrode is based on the principle that an electric potential develops when two liquids of different pH come into contact at opposite sides of a thin glass membrane. This is a design circuit for the measurement. This is the figure of the circuit.

Amplifier U1 off sets the pH electrode by 512 mV. This is achieved by using National's LM4140A-1.0 precision micro power low-dropout voltage reference that produces an accurate 1.024V. That voltage is divided in half to equal 512 mV by the 10 kΩ resistor divider. The output of amplifier U1, which is set up in a unity-gain configuration, biases the reference electrode of the pH electrode with the same voltage, 512 mV, at low impedance. The pH-measuring electrode will produce a voltage which rides on top of this 512 mV bias voltage. In effect, the circuit shifts the bipolar pH-electrode signal to a uni-polar signal for use in a single-supply system. The second amplifier U2 is set up in a unity-gain configuration and buffers the output of the pH electrode. Again, a high-input impedance buffer between the pH electrode and the measurement instrument allows the circuit to interface with a greater variety of measurement instruments including those with lower input impedance. In most applications, the output voltage of the pH electrode is high enough to use without additional amplification. If amplification is required, this circuit can easily be modified by adding gain resistors to U2.

Simple Emitter Follower Driver with Speed-Up Capacitor

This is a design circuit for follower driver circuit. This circuit is give illustrated an alternate method to reverse bias the MOSFET during turn-off by inserting a capacitor in series with the pulse transformer. The capacitor also ensures that the pulse transformer will not saturate due to DC bias. This is the figure of the circuit;

This is s simplest form design circuit. The Opto-isolators may also be used to drive power MOSFETs but their long switching times make them suitable only for low frequency applications. [Circuit source: National Semiconductor Notes].

Simple Programmable Current Source/Regulator Circuit

This is a simple circuit of programmable current source/regulator. This circuit is used to generate current. This is the figure of the circuit;

This circuit uses L 200 as main component. The error amplifier of this circuit is disabled by shorting pin 4 to ground. The value R is used to fix the output Io :

Io=(V5-2)/R
The output voltage can reach a maximum value Vi
– Vdrop=Vi 2 V (Vdrop depends on Io ).

Simple Stable Low Frequency Crystal Oscillator Circuit

This is the design circuit for a Colpitts-crystal oscillator circuit. It is suitable for low frequency crystal oscillator circuits. Using the 2N3823 JFET, this circuit has excellent stability because the temperature will not vary the 2N3823 JFET circuit loading. This is the figure of the circuit.

This is a simple form circuit for the oscillator. [Circuit Schematic Source: National Semiconductor Application Note]

Simple Current Monitor Circuit

This is a simple design circuit for monitoring and detecting the current flow. This circuit is based on LM301A and FET. This is the figure of the circuit;

On the circuit diagram, R1 is used to senses current flow of a power supply. We could use JFET as a buffer because Id=Is, therefore the power supply current flow is accurately reflected by the output monitor.

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 Step-up PWM DC-DC Converter Integrated with 4 Buffers

This is a circuit for converter that is a simple form for DC to DC Converter circuit. This circuit is based on LM2711 from National Semiconductor. This is the figure of the circuit;

The LM2711 has a current mode PWM step-up DC/DC converter with a 1.4A, 0.17 internal switch. Capable of generating 8V at 300mA from a Lithium Ion battery, the LM2711 is ideal for generating bias voltages for large screen LCD panels. The LM2711 can be operated at switching frequencies of 600 KHz or 1.25MHz, allowing for easy filtering and low noise. An external compensation pin gives the user flexibility in setting frequency compensation, which makes possible the use of small, low ESR ceramic capacitors at the output. The LM2711 uses a patented internal circuitry to limit startup inrush current of the boost switching regulator without the use of an external soft start capacitor. An external soft start pin enables the user to tailor the soft start to a specific application. The LM2711 contains 4 Gamma buffers capable of supplying 50mA source and sink. The TSSOP-20 package ensures a low profile overall solution. [Schematic circuit source: National Semiconductor Notes]

Simple Precision Power Regulator Circuit

Making a precision voltage source is easy, but not so easy if the voltage should be consistent over wide range of ambient temperature. Such requirement might be needed in high precision measurement system, for providing reference voltage in analog to digital conversion for example. This is a design circuit for precision power regulator. This is the figure of the circuit;

This circuit is based on LM 336. LM336 voltage references are easier to use than zener diodes. Their low impedance and wide current range facilitate biasing in any circuits. Besides, the breakdown voltage or the temperature coefficient can be adjusted so as to optimize the performance of the circuit. [Circuit diagram source: STMicroelectronics Application Note]

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 Microphone Amplifier Circuit

This is a circuit diagram of a device which can hear faint sounds and those sounds which any normal microphone can not hear. This is a very useful circuit and one can use this circuit for many tasks this circuit can be used as a hearing aid. Use direct coupling and do not use bulky coupling or bypass capacitors. The circuit using only a few components the size of the circuit is very small so one can easily fit it in a small box. This is the figure of the circuit;

Capacitor 1 bypasses ac negative feedback due to which the gain is not affected. Q1, Q2 and Q3 are bc 337. Resistor 1 is used for volume control. Transistor 1, transistor 2 and transistor 3 all are direct coupled amps. Their operation is stabilized by direct current (DC) negative feed back through resistor 4.

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 Lie Detector Circuit

If you want to know someone is lying or not we can use lie detector. This is a simple lie detector that can be made in minutes. It works to detect someone who telling lie but it is not as sophisticated as the ones the professionals use. This is the figure of the circuit;

The skin resistance will go down when someone telling lie and this circuit works by measuring it. We can use electrode pads, alligator clips, or just wires and tape as the electrodes. We have to adjust R2 to position the meter at the center at the beginning of the interrogation (relax condition), then we can know someone is lying when the meter changes in response to a question.

[Schematic circuit source: aaroncake.net]

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.

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.

Simple Shunt Voltage Stabilizer Circuits

This is a circuit for a simple voltage stabilizer circuit that employs a zener diode and a single resistor. In this circuit, the zener diode, which is the stabilizing component, is in parallel (or in shunt) with the load, which is why it is also called a shunt stabilizing circuit. This is the figure of the circuit;

The value of R must be chosen so that a 'holding current' of 2 mA will flow into the zener diode even at the lowest input voltage and maximum load current. The zener diode maintains the output voltage level by 'conducting' the excess current to ground whenever the voltage across it becomes excessive.

Simple Series Voltage Stabilizer Circuits

This is a circuit for simple voltage stabilizer circuit that employs a resistor, a zener diode, and an NPN transistor. In this circuit, the zener diode is used to stabilize the base voltage of the NPN transistor, which carries the load current. This is the figure of the circuit;

The load transistor is in series with the load, which is why this circuit is also known as a series stabilizer. Unlike the amplified zener shunt stabilizer, the dissipation of the transistor increases only when the actual load current increases, making its operation more efficient.

Simple OP90 Single Op Amp Full-Wave Rectifier

This is a design circuit for a full-wave rectifier circuit that provides the absolute value of input signals up to ±2.5 V even though operated from a single 5 V supply. This is the figure of the circuit;

The amplifier acts as a unity-gain inverter for negative inputs. The op amp output is forced by positive signal to ground. The 1N914 diode becomes reversed-biased and the signal passes through R1 and R2 to the output. Load impedance cause an asymmetric output since output impedance is dependent on input polarity. This can be corrected by reducing R2 for constant load impedance. A second OP90 can buffer varying or heavy loads. The output of the full-wave rectifier with a 4 Vp-p, 10 Hz input signal also shown in figure below. [Circuit's schematic diagram source: analog.com]

Simple Negative Feedback Series Voltage Stabilizer Circuit

| author: Free schematics and tools

This is a design circuit for more complex series voltage stabilizer circuit, utilizing an operational amplifier (IC1) to 'slow down' or turn off the load transistor Q1 when the output voltage is excessive. This is the figure of the circuit;

The zener diode ZD1 in this circuit is just used as a reference voltage for defining the threshold at which the op amp will turn Q2 and Q1 on or off. Because of this negative feedback mechanism, power is consumed more efficiently, since the load is only supplied with current when it needs it.

Simple Light Activated Buzzer Circuit

This is a circuit for a simple buzzer circuit that is activated by light, i.e., the buzzer is on when there's ample light and off when it is dark. A general-purpose operational amplifier, the 741, is used as a comparator that determines whether there's enough light to turn on a self-oscillating piezoelectric buzzer. Its non-inverting input is connected to a photo resistor, a component whose resistance decreases as more light shines on it. Its inverting input, on the other hand, is connected to an almost fixed voltage, i.e., a proportion of the supply voltage as set by trimmer resistor R2. This is the figure of the circuit;

If there isn't enough light shining on the photo resistor, the buzzer is quiet. As more light shines on the photo resistor, its resistance decreases and causes the voltage across R1 to increase. At a certain level of lighting, the voltage across R1, which is also the voltage at the non-inverting input of the 741, becomes larger than the voltage at the inverting input. At this point, the 741 is triggered to output a 'high' level, turning on Q1. Q1 then activates the self-oscillating piezoelectric buzzer.