Operational Amplifier (Op-Amp) Basics Circuit

Circuit Diagram 

Inverting Amplifier:

 The op-amp is connected using two resistors RA and RB such that the input signal is applied in series with RA and the output is connected back to the inverting input through RB. The noninverting input is connected to the ground reference or the center tap of the dual polarity power supply. In operation, as the input signal moves positive, the output will move negative and visa versa. The amount of voltage change at the output relative to the input depends on the ratio of the two resistors RA and RB. As the input moves in one direction, the output will move in the opposite direction, so that the voltage at the inverting input remains constant or zero volts in this case. If RA is 1K and RB is 10K and the input is +1 volt then there will be 1 mA of current flowing through RA and the output will have to move to -10 volts to supply the same current through RB and keep the voltage at the inverting input at zero. The voltage gain in this case would be RB/RA or 10K/1K = 10. Note that since the voltage at the inverting input is always zero, the input signal will see a input impedance equal to RA, or 1K in this case. For higher input impedances, both resistor values can be increased.

Noninverting Amplifier:

 The noninverting amplifier is connected so that the input signal goes directly to the noninverting input (+) and the input resistor RA is grounded. In this configuration, the input impedance as seen by the signal is much greater since the input will be following the applied signal and not held constant by the feedback current. As the signal moves in either direction, the output will follow in phase to maintain the inverting input at the same voltage as the input (+). The voltage gain is always more than 1 and can be worked out from Vgain = (1+ RB/RA).

Voltage Follower:
 The voltage follower, also called a buffer, provides a high input impedance, a low output impedance, and unity gain. As the input voltage changes, the output and inverting input will change by an equal amount.
Source-  http://www.bowdenshobbycircuits.info/

06:00 0 comments

Speed-limit Alert Circuit

Wireless portable unit
Adaptable with most internal combustion engine vehicles
Circuit Diagram

Parts:

• R1,R2,R19 1K 1/4W Resistors
• R3-R6,R13,R17 100K 1/4W Resistors
• R7,R15 1M 1/4W Resistors
• R8 50K 1/2W Trimmer Cermet
• R9 470R 1/4W Resistor
• R10 470K 1/4W Resistor
• R11 100K 1/2W Trimmer Cermet (see notes)
• R12 220K 1/4W Resistor (see notes)
• R14,R16 68K 1/4W Resistors
• R18 22K 1/4W Resistor
• R20 150R 1/4W Resistor (see notes)
• C1,C7 100µF 25V Electrolytic Capacitors
• C2,C3 330nF 63V Polyester Capacitors
• C4-C6 4µ7 25V Electrolytic Capacitors
• D1,D5 Red LEDs 3 or 5mm.
• D2,D3 1N4148 75V 150mA Diodes
• D4 BZX79C7V5 7.5V 500mW Zener Diode
• IC1 CA3140 or TL061 Op-amp IC
• IC2 4069 Hex Inverter IC
• IC3 4098 or 4528 Dual Monostable Multivibrator IC
• Q1,Q2 BC238 25V 100mA NPN Transistors
• L1 10mH miniature Inductor (see notes)
• BZ1 Piezo sounder (incorporating 3KHz oscillator)
• SW1 SPST Slider Switch
• B1 9V PP3 Battery (see notes)
• Clip for PP3 Battery 

 Device Purpose:

 This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine.

Circuit operation:

 IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

Notes:

• D1 is necessary at set-up to monitor the sparking-plugs emission, thus permitting to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery saving.
• During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K.
• You must do this first setting when the engine is on but the vehicle is stationary.
• The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5. Reducing car's speed the beep must stop.
• L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil.
• Circuit's current drawing is approx. 10mA. If you intend to use the car's 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R.
• Depending on the engine's cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less.
• If you need to set-up the device on the bench, a sine or square wave variable generator is required.
• To calculate the frequency relation to RPM in a four strokes engine you can use the following formula:
• Hz= (Number of cylinders * RPM) / 120.
• For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60.
• Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz.
• Temporarily disconnect C2 from IC1's pin 6. Connect the generator's output to C2 and Ground. Set the generator's frequency to i.e. 100Hz and regulate R11 until you hear the beeps and LED D5 flashes. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.
• This circuit is not suited to Diesel engines. 

Author: RED Free Circuit Designs
Source http://www.redcircuits.com/

05:54 0 comments

18 Stage LED Sequencer Circuit

Description 

The question sometimes comes up of how to cascade 4017 decade counters for more than 10 sequencial stages. The LED sequencer below shows a possible solution using a few extra parts.

When power is applied, the 15K resistor and 10uF cap at pin 15 will reset the counters to the zero count where pin 3 is at +12 and all other outputs are at zero. The 2 diodes (1n914) and 15 resistor form a AND gate so the clock pulse will be passed to the right side counter when the sequence starts. When the right counter reaches the 10th count, pin 11 will move high enabling the AND gate on the right to pass the clock pulse to the left side counter. As the left side counter advances, pin 3 will be low so that clock pulses cannot advance the right counter. When the left counter turns over and pin 3 again moves high, the sequence will repeat. Thus we get 18 total counts, 9 from the first counter, and 9 from the second.

Circuit Diagram

 Note that the 4017 counter will not deliver much current, and so the LED current is set to about 6mA using a 1.5K resistor in series. For more current, you could use transistors on each output as shown in the drawing above, (10 Channel LED Sequencer). But some of the newer bright LEDs are fairly bright at 6mA.

06:14 0 comments

Multitone Siren Circuit

Description 

This multi-tone siren is useful for burglar alarms, reverse horns, etc. It produces five different audio tones and is much more ear-catching than a single-tone siren. The circuit is built around popular CMOS oscillator-cum-divider IC 4060 and small audio amplifier LM386. IC 4060 is used as the mult-itone generator. A 100µH inductor is used at the input of IC 4060. So it oscillates within the range of about 5MHz RF. IC 4060 itself divides RF signals into AF and ultrasonic ranges. Audio signals of different frequencies are available at pins 1, 2, 3, 13 and 15 of IC 4060 (IC1).

Circuit Diagram:

These multi-frequency signals are mixed and fed to the audio amplifier built around IC LM386. The output of IC2 is fed to the speaker through capacitor C9. If you want louder sound, use power amplifier TBA810 or TDA1010. Only five outputs of IC1 are used here as the other five outputs (pins 4 through 7 and 14) produce ultrasonic signals, which are not audible. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Regulated 6V-12V (or a battery) can be used to power the circuit.

 Author: PradeeP G., Elektor Electronics Magazine
Source http://www.extremecircuits.net/2010/05/multitone-siren.html

06:05 0 comments

Midnight Security Light Circuit Schematic

Description 

Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep. Here is an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am. It automatically resets in the morning. The circuit is fully automatic and uses a CMOS IC CD 4060 to get the desired time delay. Light-dependent resistor LDR1 controls reset pin 12 of IC1 for its automatic action. During day time, the low resistance of LDR1 makes pin 12 of IC1 ‘high,’ so it doesn’t oscillate.

After sunset, the high resistance of LDR1 makes pin 12 of IC1 ‘low’ and it starts oscillating, which is indicated by the fashing of LED2 connected to pin 7 of IC1. The values of oscillator components (resistors R1 and R2 and capacitor C4) are chosen such that output pin 3 of IC1 goes ‘high’ after seven hours, i.e., around 1 am. This high output drives triac 1 (BT136) through D5 and R3. Bulb L1 connected between the phase line and M2 terminal of triac 1 turns on when the gate of triac 1 gets the trigger voltage from pin 3 of IC1. It remains ‘on’ until pin 12 of IC1 becomes high again in the morning. Capacitors C1 and C3 act as power reserves, so IC1 keeps oscillating even if there is power interruption for a few seconds. Capacitor C2 keeps trigger pin 12 of IC1 high during day time, so slight changes in light intensity don’t affect the circuit.

Using preset P1 you can adjust the sensitivity of LDR1. Power supply to the circuit is derived from a step-down transformer T1 (230V AC primary to 0-9V, 300mA secondary), rectifed by a full-wave rectifer comprising diodes D1 through D4 and fltered by capacitor C1. Assemble the circuit on a general-purpose PCB with adequate spacing between the components. Sleeve the exposed leads of the components. Using switch S1 you can turn on the lamp manually. Enclose the unit in a plastic case and mount at a location that allows adequate daylight.

Circuit Diagram:

Parts:

• P1 = 100K
• R1 = 120K
• R2 = 1M
• R3 = 100R
• R4 = 100R
• C1 = 1000uF-25V
• C2 = 100uF-25v
• C3 = 100nF-63V
• C4 = 1uF-25V
• D1 = 1N4001
• D2 = 1N4001
• D3 = 1N4001
• D4 = 1N4001
• D5 = Red LED
• D6 = Green LED
• IC = CD4060
• TR = BT136
• T1 = 9v 300mA Transformer
• L1 = 230V-60W Bulb
• SW = On/Off Switch 

Caution:

 Since the circuit uses 230V AC, many of its points are at AC mains voltage. It could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to construct this circuit. We will not be responsible for any kind of resulting loss or damage.

Source - http://www.extremecircuits.net/2010/01/midnight-security-light-circuit.html

06:16 0 comments

Pulse Width Modulation DC Motor Control Circuit

Description 

 Often, people attempt to control DC motors with a variable resistor or variable resistor connected to a transistor. While the latter approach works well, it generates heat and hence wastes power. This simple pulse width modulation DC motor control eliminates these problems. It controls the motor speed by driving the motor with short pulses. These pulses vary in duration to change the speed of the motor. The longer the pulses, the faster the motor turns, and vice versa.

Circuit Diagram

Parts

• R1 1 Meg 1/4W Resistor
• R2 100K Pot
• C1 0.1uF 25V Ceramic Disc Capacitor
• C2 0.01uF 25V Ceramic Disc Capacitor
• Q1 IRF511 MOSFET or IRF620
• U1 4011 CMOS NAND Gate
• S1 DPDT Switch
• M1 Motor (See Notes)
• MISC Case, Board, Heatsink, Knob For R2, Socket For U1

Notes

• R2 adjusts the speed of the oscillator and therefore the speed of M1.
• M1 can be any DC motor that operates from 6V and does not draw more than the maximum current of Q1. The voltage can be increased by connecting the higher voltage to the switch instead of the 6V that powers the oscillator. Be sure not to exceed the power rating of Q1 if you do this.
• Q1 will need a heatsink.
• Q1 in the parts list can handle a maximum of 5A. Use the IRF620 for 6A, if you need any higher. 

Source -http://www.aaroncake.net/

06:13 0 comments

Sound Effects Generator Circuit

Description: 
 This circuit uses a UM3561 IC to produce four different sound effects.
Circuit Diagram

Notes:

 Nothing too complicated here. The IC produces all the sound effects, the output at Pin 3 being amplified by the transistor. A 64 ohm loudspeaker can be substituted in place of the 56 ohm resistor and 8 ohm loudspeaker. The 2 pole 4 way switch controls the sound effects. Position 1 (as drawn) being a Police siren, position 2 is a fire engine sound, 3 is an ambulance and position 4 is a machine gun effect. The IC is manufactured by UMC and was available from Maplin electronics code UJ45Y. At the time of writing this has now been discontinued, but they have have limited stocks available.

Author: Andy Collinson, anc@mitedu.freeserve.co.uk
Source http://www.zen22142.zen.co.uk/

06:13 0 comments