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Showing posts with label 555. Show all posts

Thursday, September 25, 2014

Schmitt Trigger Using IC 555

Several circuits exist for using NE 555 as a Schmitt trigger.The circuits are s0 arranged that when the voltage exceeds aset value, say V1, the output of NE 555 becomes high. When the voltage falls below, say V2, the output becomes low. Almost all such circuits use the internal hysteresis pro- vided by ·the three 5k resistors. Though such circuits are simple to design, the Schmitt trigger action of such circuits puts a limitation on the designer. In such circuits, for exam- ple, the difference between Vl ( the upper trip point) and V2 {the lower trip point) is fixed at l/ 3 Vcc by the internal potential divider, and this difference cannot be varied. The circuit shown in Fig. 1 avoids this limitation.

lt enables the use of an NE555 as a general-purpose Schmitt trigger with externally adjustable characteristics. Rl and R2 form a potential divider of Vcc and apply a voltage V1 = R1/R1+R2 * Vcc to terminal 6. Similarly, a voltage V2 = R3/R3+R4 * Vcc is applied to terminal 2. The input voltage Vi is applied to terminal 5 (negative . terminal of threshold comparator).

Also, the input voltage V1 is divided into half (by the internal 5k resistors) and is applied to the positive terminal of the trigger comparator. When the input voltage exceeds twice the value of V2, the trigger comparator output becomes high and the output of NE555 becomes high. After exceeding twice the value of V2, if the input voltage reduces, no change in the timer output occurs until the input voltage goes below VI. When the input goes below V1, the threshold comparator output goes high and the timer output goes low. Thus the NE555 acts as a Schmitt trigger with adjustable hysteresis points of 2 XSV2 and Vl. ’ .

Care should be taken to keep 2xV2 larger than Vl, as is expected from any Schmitt trigger. If this is not satisfied, the timer will not behave as a Schmitt trigger but will operate as a simple comparator (with 2xV2 as the comparison voltage). Another important point is that the internal impedance of the input voltage should be very low, so that the voltage at negative input of the threshold comparator is now significantly modified by the internal potential dividing resistors

(connected to Vcc and earth).
A typical circuit is given in Fig. 2 along with input and
output waveforms.

Simple Capacitive Switch Circuit Using IC 555

Take a square wave signal with a given frequency and integrate it. This gives a stable continuous average voltage.
By changing the existing frequency of the signal the average integrated value remains the same but, at the instant when the frequency is changed, a positive or negative voltage peak will appear due to the momentary change in the average waveform of the signal. This is the principle upon which our switch is based. The 555 or 7555 timers will oscillate in a stable manner. However, if we add an external capacitive sensor it becomes possible to vary the oscillation frequency. ln this circuit the square wave is integrated by the triple RC network, while IC2, used as a comparator (with a variable reference value), uses the changes in the integrated voltage to alternately make and break the relay.

Thus when you e move close to C the relay makes; if you remain stationary the relay breaks. It may seem a blt basic but it is a valid idea and it is worth l looking at it in greater detail. To obtain better results you could take the signal after integration and differentiate between negative pulses (the frequency decreases as the value of C increases: when the sensor is approached) and positive pulses (the frequency increases again if the sensor is no longer affected) and compare them. Without this l refinement the size of the sensitive plate must be such that the frequency of oscillation be at least several kHz. Failing this the operation of the circuit would often be disrupted by false detections. Coarse and fine adjustment is provided, using P1 and P2, to reduce the risk of incorrect switching. Note: The numbers in parentheses are the pins if an LM3l1 is used in place of the CA3130

Wednesday, September 17, 2014

Electronic Door Minder using 555 Timer

Circuit Diagram

door-minder-transmitter-Circuit

Electronic Door Minder using 555 Timer Transmitter Circuit Diagram

Because the IR beam is very strong distances over 25 yards can be monitored with electronic circuit . This circuit must be powered from a 12volt DC supply. The transmitter circuit consists of two square-wave oscillators, one running at approx. 250Hz and the other running at 38kHz. The 38kHz frequency acts as a carrier wave and is required by the IR receiver module on the receiver board.The oscillators are made by using two 555 timer ICs set up as astable configuration multivibrators.Another 555 timer ( IC2) is used for the 38KHz oscillator. Resistors R4 and R5 and capacitor C3 set the frequency.Diodes D1 and D3 are used to create a symmetrical output.

Circuit diagram :

door-minder-receiver-circuit

Electronic Door Minder using 555 Timer Receiver Circuit Diagram

Normally the external capacitor C1 (C3) charges through resistors R1 and R2 (R4 and R5) and discharges through R2 (R5). Without the diodes this output waveform would have a longer “high” time than the “low” time. The output from the IC1 is coupled via diode D2 and resistor R3 to the trigger input of IC2. When the IC1 output is low it stops IC2 from running and IC2’s output is forced high (no IR LED current). When IC1 output is high, IC2 runs and the IR LED is pulsed at 38KHz.The receiver module consists of an IR receiver module that detects the incoming beam from the transmitter. The IR signal is used to keep a capacitor charged which in turn holds a relay operated. When the beam is broken the capacitor discharges and the relay releases.

Saturday, September 6, 2014

Electronic Door Minder using 555 Timer

This door minder electronic project uses an IR beam to monitor door & passage-ways or any other area. When the IR beam is broken a relay is tripped which can be used to sound a bell or alarm. This door minder electronic project is suitable for detecting customers entering a shop, cars coming up a driveway, etc. Circuit Diagram Electronic Door Minder using 555 Timer Transmitter Circuit Diagram Because the IR beam is very strong distances over 25 yards can be monitored with electronic schema . This schema must be powered from a 12volt DC supply. The transmitter schema consists of two square-wave oscillators, one running at approx. 250Hz and the other running at 38kHz. The 38kHz frequency acts as a carrier wave and is required by the IR receiver module on the receiver board.The oscillators are made by using two 555 timer ICs set up as astable configuration multivibrators.Another 555 timer ( IC2) is used for the 38KHz oscillator. Resistors R4 and R5 and capacitor C3 set the frequency.Diodes D1 and D3 are used to create a symmetrical output. Circuit diagram : Electronic Door Minder using 555 Timer Receiver Circuit Diagram

Tuesday, August 19, 2014

Simple Astable 555 Timer IC Flasher

For a lower parts count than the 2 transistor multivibrators, 2 LEDs can be alternately flashed with a 555 integrated schema configured as shown in Schematic 2. I chose the combination of a 2K2 and a 47K resistor to determine the oscillation frequency along with the 10 uF capacitor connected to pins 2 and 6. You can practically change the (R Speed) 47K value to between 10K and 100K or more. Greater resistance = lower speed. You may also wish to connect up a 100K or so potentiometer instead of the 47K resistor for a variable speed version. Additionally, the 10 uF capacitor value can be changed. Feel free to experiment.

Although, alternately flashing LEDs is great for the beginner to electronics, the basic one ON, one OFF schema gets boring quickly. In the next section, we will try to improve the look and try to approximate a flash like a police car (within limits).

Wednesday, August 13, 2014

Police Sirine Circuit with IC 555

The series of police sirens with 555 ic this is a series of sirens that utilizes two IC 555 as a pulse generator and producing shrill voice.

Both ic 555 respectively build the astable multivibrator circuit and generate output signals with different frequencies. It is intended to be used as one of the high frequency generator or a screeching sound and the other as a regulator of the swing from last shrill voice. If we observe the working principle of this circuit is very similar to a series of modulation fm. Where the shrill sound signal likened to a high frequency signal from the oscillator circuit and control signal swing is the wail of the information signal or input signals that will transmit. This is consistent with the shape of the output signal associated with the loudspeaker, which has an output signal frequency changes in the form of regular meetings wave tenuous.

Actually a series of sirens could be simpler than if you use a 556 IC which is a dual multivibrator or equal to two pieces of IC 555. IC 556 has two multivibrator circuit menfaatkan so you can meet the workflow of this siren sound-producing circuit. Or you can also make it by using a combination of multiple transistors. And it could be you do remember the oscillator circuit can be easily made with transistors.

Appropriate image above then:

R1, R2, and C1 is a determinant of the frequency of the signal generated by IC1

R3, R4 and C3 is a determinant of the signal frequency whine

Signals generated by IC1 IC2 pin 5 connected to the control signals intended for the resulting shrieks

Screeching sound signal will swing to follow the control of the output signal IC1

You can do experiments in order to gain more understanding of police sirens this circuit by changing the value of some critical components such as the frequency of R1, R2, R3, R4, C1 and C3.