Touch Switch II Circuit Diagram

This circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in the Learning section on my site. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

Read More

IC 555 Design Note

The popular Timer IC 555 is extensively used in short duration timing applications. IC 555 is a highly stable integrated circuit functioning as an accurate time delay generator and free running multivibrator. But one of the serious problem in 555 timer design is the false triggering of the circuit at power on or when voltage changes. The article describes how IC555 is designed perfectly to avoid false triggering.

555 IC pin functions

Pin1 Ground
Pin2 Trigger
Pin3 Output
Pin 4 Reset
Pin 5 Control voltage
Pin 6 Threshold
Pin 7 Discharge
Pin 8 Vcc

Functional aspects of pins

Trigger Pin 2

Usually pin2 of the IC is held high by a pull up resistor connected to Vcc. When a negative going pulse is applied to pin 2, the potential at pin 2 falls below 1/3 Vcc and the flip-flop switches on. This starts the timing cycle using the resistor and capacitor connected to pins 6 and 7.

Reset pin 4

Reset pin 4 can be controlled to reset the timing cycle. If pin 4 is grounded, IC will not be triggered. When pin4 becomes positive, IC becomes ready to start the timing cycle. Reset voltage is typically 0.7 volts and reset current 0.1 mA. In timer applications, reset pin should be connected to Vcc to get more than 0.7 volts.

Control Voltage pin 5

Pin5 can be used to control the working of IC by providing a DC voltage at pin5. This permits the control of the timing cycle manually or electronically. In monostable operation, the control pin5 is connected to ground through a 0.01 uF capacitor. This prevents the timing interval from being affected by AC or RF interference. In the Astable mode, by applying a variable DC voltage at pin 5 can change the output pulses to FM or PWM.

Threshold pin 6 and Discharge pin 7

These two inputs are used to connect the timing components- Resistor and Capacitor. The threshold comparator inside the IC is referenced at 2/3 Vcc and the trigger comparator is referenced at 1/3 Vcc. These two comparators control the internal Flip-Flop of the circuit to give High or Low output at pin 3.When a negative going pulse is applied to pin 2, the potential at pin2 drops below 1/3 Vcc and the trigger comparator switches on the Flip-Flop. This turns the output high. The timing comparator then charges through the timing resistor and the voltage in the timing capacitor increases to 2/3 Vcc.( The time delay depends on the value of the resistor and capacitor.

That is, higher values, higher time).When the voltage level in the capacitor increases above 2/3 Vcc, the threshold comparator resets the Flip-Flop and the output turns low. Capacitor then discharges through pin 7.Once triggered, the IC will not responds to further triggering until the timing cycle is completed. The time delay period is calculated using the formula T= 1.1 Ct Rt. Where Ct is the value of Capacitor in PF and Rt is the value of Resistor in Ohms. Time is in Seconds.

How to eliminate false triggering?

The circuit diagram shown below is the simple monostable using IC 555. To eliminate the false triggering resistor R1 and Capacitor C1 are connected to the reset pin 4 of the IC. So the reset pin is always high even if the supply voltage changes. Moreover capacitor C3 connected close to the Vcc pin 8 acts as a buffer to maintain stable supply voltage to pin 8. Using this design, it is easy to avoid false triggering to a certain extent.

555 Monostable circuit

A ready recknor to select timing resistor and capacitor

Theoretically long interval is possible with IC 555,but in practical conditions, it is difficult to get more than 3 minutes. If low leakage Tantalum capacitor is used, this can be increased to 5 minutes or more. If the value of the timing capacitor is too high above 470 uF, charging time will be prolonged which will upset the timing cycle and the output remains high even after the desired time is over.

Streampowers

Read More

40 LED Bicycle Light Circuit Diagram

The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer. A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage.

Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20mA of current for a total of 220mA. The circuit should work with additional LEDs up to about 40 for each group, or 81 total. The circuit will also work with fewer LEDs so it could be assembled and tested with just 5 LEDs (two groups of two plus one) before adding the others.

Read More

Police Lights associate crystal rectifier Project

This circuit uses a 555 timer that is setup to each runn in associate Astable operative mode. This generates a nonstop output via Pin three within the type of a sq. wave. once the timer's output changes to a high state this triggers the a cycle the 4017 4017 decade counter telling it to output consecutive sequent output high. The outputs of the 4017 ar connected to the LEDs turning them on and off.

Schematic


Parts List

1x - NE555 Bipolar Timer
1x - 4017 Decoded Decade
6x - 1N4148 Diode
1x - 1K Resistor (1/4W)
1x - 22K Resistor (1/4W)
2x - 4.7K Resistor (1/4W)
6x - 470 Resistor (1/4W)
1x - 2.2µF Electrolytic Capacitor (16V)
2x - BC547 NPN Transistor
2x - LED (Blue)
2x - LED (Red)
1x - 9V Voltage Battery 

Streampowers

Read More

Pure Sine Wave Inverter, Using IC 555

The proposed circuit generates accurately spaced PWM pulses which imitates a sine wave very closely and thus can be considered as good as its sine wave counter part design. Here we use  two stages for creating the required  PWM pulses, the stage comprising the ICs 741 and the other comprising the IC 555. Let’s learn the whole concept in details.

How the Circuit Functions – The PWM Stage

The circuit diagram can be understood with the following points:

The two op amps are basically arranged to generate the required sample source voltages for the IC 555. 

The couple of outputs from this stage is responsible for the generation of square waves and triangular waves.

The second stage which is actually the heart of the circuit consists of the IC 555. Here the IC is wired in a monostable mode with the square waves from the op amp stage applied to its trigger pin #2 and the triangular waves applied to its control voltage pin # 5.

The square wave input triggers the monostable to generate a chain of pulses at the output where as the triangular signal modulates the width of this output square wave pulses.

The output from the IC 555 now follows the “instructions” from the op amp stage and optimizes its output in response to the two input signals, producing the sine equivalent PWM pulses.

Now it’s just a matter of appropriately feeding the PWM pulses to the output stages of an inverter consisting of the output devices, the transformer and the battery.

The Output Stage

The above PWM output is applied to the output stage as shown in the figure.

Transistors T1 and T2 receive the PWM pulses at their bases and switch the battery voltage into the transformer winding according to the duty cycles of the PWM optimized waveform.

The other two transistors make sure that the conduction of T1 and T2 takes place in tandem, that is alternately so tat the output o from the transformer generates one complete AC cycle with the two halves of the PWM pulses.

Parts List

R1, R2, R3, R8, R9, R10 = 10K,

R7 = 8K2,

R11, R14, R15, R16 = 1K,

R12, R13 = 33 Ohms 5 Watt,

R4 = 1M preset,

R5 = 150 K preset,
R6 = 1K5

C1 = 0.1 uF,

C2 = 100 pF,

IC1 = TL 072,

 IC2 = 555,

T1, T2 = BDY29,

T5, T6 = TIP 127,

T3, T4 = TIP122

Transformer = 12 – 0 – 12 V, 200 Watts,

Battery = 12 volts, 100 AH.

Source by Link

Read More

555 Timer - Frequency and Duty Cycle Calculator

Enter values for R1, R2, and C and press the calculate button to solve for positive time interval (T1) and negative time interval (T2). For example, a 10K resistor (R1) and 100K (R2) and 0.1 uF capacitor will produce output time intervals of 7.62 mS positive (T1) and 6.93 mS negative (T2). The frequency will be about 70 Hz. R1 should be greater than 1K and C should be greater than .0005 uF. Scroll down page for basic 555 information (pinout and two basic circuits).

Positive Time Interval (T1) = 0.693 * (R1+R2) * C
Negative Time Interval (T2) = 0.693 * R2 * C
Frequency = 1.44 / ( (R1+R2+R2) * C) 

First introduced by the Signetics Corporation as the SE555/NE555 about 1971.Pin connections and functions: (See schematic below for basic circuits)

Pin 1 (Ground)    - The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common when operated from positive supply voltages.

Pin 2 (Trigger)   - This pin is the input which causes the output to go high and beginthe timing cycle. Triggering occurs when the trigger input movesfrom a voltage above 2/3 of the supply voltage to a voltage below1/3 of the supply. For example using a 12 volt supply, the triggerinput voltage must start from above 8 volts and move down to avoltage below 4 volts to begin the timing cycle. The action islevel sensitive and the trigger voltage may move very slowly. Toavoid retriggering, the trigger voltage must return to a voltageabove 1/3 of the supply before the end of the timing cycle in themonostable mode. Trigger input current is about 0.5 microamps.

Pin 3 (Output)    - The output pin of the 555 moves to a high level of 1.7 volts less than the supply voltage when the timing cycle begins. The output returns to a low level near 0 at the end of the cycle. Maximum current from the output at either low or high levels is approximately 200 mA.

Pin 4 (Reset):    - A low logic level on this pin resets the timer and returns the output to a low state. It is normally connected to the + supply line if not used.

Pin 5 (Control)   - This pin allows changing the triggering and threshold voltages by applying an external voltage. When the timer is operating in the a stable or oscillating mode, this input could be used to alter or frequency modulate the output. If not in use, it is recommended installing a small capacitor from pin 5 to ground to avoid possible false or erratic triggering from noise effects.

Pin 6 (Threshold) - Pin 6 is used to reset the latch and cause the output to go low.Reset occurs when the voltage on this pin moves from a voltage below 1/3 of the supply to a voltage above 2/3 of the supply.The action is level sensitive and can move slowly similar to the trigger voltage.

Pin 7 (Discharge) - This pin is an open collector output which is in phase with the main output on pin 3 and has similar current sinking capability.

Pin 8 (V +)       - This is the positive supply voltage terminal of the 555 timer IC.Supply-voltage operating range  is +4.5 volts (minimum) to +16volts (maximum).

The pin connections for the 556 which is a dual 555 timer (2 in one package) areshown in table below. For example, the two outputs for the two timers of the 556 areon pins 5 and 9 which correspond to the output pin 3 of the 555. 

555      556 timer #1        timer #2

Ground         1                  7               7 

Trigger        2                  6               8

Output         3                  5               9

Reset          4                  4               10

Control        5                  3               11

Threshold      6                  2               12

Discharge      7                  1               13+ 

Power Vcc    8                  14              14

The schematics below show the two basic circuits for the 555 timer.

Below is a pictorial view of the 555 timer wired as a LED flasher and powered with a 9 volt battery. The LED will turn on during time T1 and off during time T2.

The 555 circuit below is a flashing bicycle light powered with three C or D cells (4.5 volts). The two flashlight lamps will alternately flash at a approximate 1.5 second cycle rate. Using a 4.7K resistor for R1 and a 100K resistor for R2 and a 4.7uF capacitor, the time intervals for the two lamps are 341 milliseconds (T1, upper lamp) and 326 milliseconds (T2 lower lamp). The lamps are driven by transistors to provide additional current beyond the 200 mA limit of the 555 timer. A 2N2905 PNP and a 2N3053 NPN could be used for lamps requiring 500 mA or less. For additional current, a TIP29 NPN and TIP30 PNP could be used up to 1 amp. A PR3 is a 4.5 volt, 500 mA flashlight bulb. Two diodes are placed in series with the PNP transistor base so that the lower lamp turns off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the two diodes increases the forward voltage required for the PNP transistor to about 2.1 volts so that the 1.7 volt difference from supply to the output is not enough to turn on the transistor. You can also use an LED in place of the two diodes as shown in the lower schematic.

Read More

Visitor Alarm Circuit Diagram Using IC 555

Description

                  Figure shows the circuit diagram of the 'Visitor Alarm' . Here I have used a LDR and a mono stable Multi Vibrator for making this circuit . When who breaking the LED ray, the LDR has high resistance so the transistor will be OFF and the pin number two of the IC 555 is negative then the IC 555 will be triggering so the output is ON. When who don't breaking the LED ray, the LDR has low resistance so the transistor will be ON and the pin number two of the IC 555 is positive after that the IC 555 doesn't triggering so the output is OFF.

Circuit Idea

Making Of LDR and LED

           Cover both items with a black insulation tape. See the below images for further details.

LED	LDR

Arrangement Of LDR and LED




Parts List 

Component No:	Value
R1	10K
R2	10K
R3	680R
R4	10K
C1	10MF
C2	103pF
Q1	BC548
D1	White LED Or LASER
	LDR
U1	NE555
B1	6V Buzzer

Read More

Police Siren Circuit Diagram

The simple Police Siren circuit uses two 555's to produce an up-down wailing sound. The first 555 is wired as a low-frequency oscillator to control the VOLTAGE CONTROL pin 5 of the second 555. The voltage shift on pin 5 causes the frequency of the second oscillator to rise and fall.

Simple Police Siren Circuit Diagram

Read More

Simple Water Sensor Circuit Diagram using IC 555

This is a water sensor /rain alarm circuit diagram; it can be used on motorcycle, car or other device that we want to protect from water, rain. This is a simple water sensor/rain alarm circuit that makes an alarm when water/rain falls on its sensor. This circuit is based on NE555/LM555 IC and two transistors (Q1&Q2). For transistor Q1- BC547 or BC107 and for Q2- 2N825,BC548 or BC168 can be used in the circuit. 

This rain detector circuit can be supplied from voltage source of +9V-12V DC. The resistor 470K ohm is a POT/Variable resistor; it is used to adjust the sensitivity of water/rain sensor. Use a 8 ohm,0.5w-1W speaker to hearing better alarm. Less than 8 ohm speaker could be harmful for the IC 555. 

Circuit Diagram of Water Sensor 

 We can make the water sensor as shown in the image (Fig-1) using aluminum conductor like a naked wire . Here can be used other conductor but we suggesting to use aluminum.

Read More

Simple Ignition Timer Circuit Diagram

This circuit is a tester for flywheel based ignition systems in small aeroplane engines. Basically the same ignition coils are also seen in other small combustion engines used in/on mopeds and lawn mowers  in brief, engines without a battery. The part to be tested comprises a primary coil in parallel with the contact breaker. The timing of this contact breaker has to be adjusted correctly.

Since the coil’s primary has a very low resistance it is difficult to determine whether the contact breaker is open or closed.  However, you can determine that reliably with this circuit, using an LED and a beeper. The circuit is implemented twice because aviation engines (Cessna, Piper and similar) always have two ignitions in parallel to increase reliability. For two-cylinder engines, well the purpose is obvious.

Ignition Timer Circuit Diagram
 

The circuit consists of a 555 and a few transistors. The 555 supplies a square wave of about 3000 Hz. This signal goes to power transistors T1 and T2; these can supply quite a bit of power and are robust enough to withstand the voltage transients from the big coils. The test connection (K2 and K3 respectively) are connected in parallel with the contact breaker to be tested, which itself is in parallel with the ignition coil. The frequency of 3000 Hz is either short circuited by the contact breaker or if the points are open  is amplified somewhat by the resonance of the coil itself.

This allows you to reliably detect the difference bet ween a closed and open contact breaker, despite the low resistance of the coil, which is in parallel with it. When the contact breaker is open the amplified pulses will turn on T3 and T4 respectively, so that the relevant LEDs turn on and the buzzer will sound.

The components are not critical, but do use a sensitive type for the piezo buzzer. The power supply is 3 V (2 times AA or AAA batteries). 

Read More

Long Duration Timer using A Ttiny 2313

This timer circuit is designed to switch on a 12 V load in a solar-powered installation for a preset period at the press of a button. When the period has expired a latching relay disconnects both the load and the controller circuit from the 12 V supply. The length of the period can be configured by making suitable changes to the microcontroller’s source code.

When button S1 is pressed a voltage appears across relay coil L1, and the relay switches the load on. Since the relay is a latching type, it remains in this state when the but ton is released. There is now a supply to the 78L05 voltage regulator (a low-dropout type such as the LP2950CZ-5.0 may also be used) and the microcontroller is powered up. In the microcontroller the timer program runs until the configured time interval has elapsed. Around 90 % of the way through the time period LED D2 lights as a warning that the load will shortly be switched off, and this time can also of course be configured by changing the software.

When the full time interval has elapsed the microcontroller sets an output (pin 7) high, which triggers the CNY 17-3 optocoupler and in turn drives relay coil L2. The relay returns to its initial state, disconnecting the load as well as the controller (which is also powered via the relay contact) from the 12 V supply.

Long Duration Timer Circuit Diagram

The author used a miniature 16 -by-2 LCD panel type HMC16223SG in his prototype, measuring just 52 mm by 20 mm. It is of course possible to use any standard LCD module that uses an HD44780-compatible controller. Note that P1 is used to adjust the contrast of the LCD: if the display appears blank it is worth checking the contrast set-ting before suspecting a more serious problem! If desired, the LCD can be dispensed with, along with the corresponding parts of the source code.

The upper line of the LCD shows the total time period, in seconds, for which the soft-ware is configured, while the lower line shows the time, in seconds, since the button was pressed.

The screendump shows the LCD settings under BASCOM-AVR. The source code for the program is available for download. Link

Read More

Using 555 Timer - Voltage Controlled Switch

In this circuit the 555 timer is used in a novel way, as a voltage controlled switch.The old and omnipresent NE555 can be very good at something it was not meant for: driving relays or other loads up to 200 mA. The picture shows an example circuit: if the input level rises over 2/3 of the supply voltage - it will turn on the relay, and the relay will stay on until the level at the input drops below one third of the supply voltage.

If the relay and D1 were connected between pin 3 and ground, the relay would be activated when the input voltage drops below one third, and deactivated when the input voltage goes over two thirds of the supply voltage. It is also a nice advantage that the input requires only about 1 uA, which is something bipolar transistors can't compete with. (This high impedance input must not be left open.) A large hysteresis makes the circuit immune to noise. The output (pin 3) can only be either high or low (voltage-wise), and it changes its state almost instantenously, regardless of the input signal shape.

Voltage Controlled Switch Circuit Diagram

The voltage drop across the NE555's output stage (at 35-100 mA) is 0.3-2.0 V, depending on the way the relay is connected and the exact current it draws. D1 is absolutely vital to the safety of the integrated circuit.

Read More

Simple 555 Timer Circuit key cod

A very simple electronic key code lock circuit that require few external components can be constructed using this schematic diagram . This electronic key code lock circuit is based on a common 555 timer circuit and some other common components .

This low cost key code circuit use six switches that needs to be pressed to open the lock, but only two switches at a time. In many other , more expensive electronic circuits the key code is formed by pressing some switches one by one , not like in this case two switches . If you don’t like to press two switches in the same time you can eliminate one switch , but in that case the code can be more easy to guess by someone ells .Thus a total of three sets of switches have to be pressed in a particular sequence. (Of these three sets, one set is repeated.)

An essential property of this electronic code lock is that it works in monostable mode, i.e. once triggered, the output becomes high and remains so for a period of time, governed by the timing components, before returning to the quiescent low state.Pin 2 of 555 timer is the triggering input pin which, when held below 1/3 of the supply voltage, drives the output to high state. The threshold pin 6, when held higher than 2/3 of the supply voltage, drives the output to low state. By applying a low-going pulse to the reset pin 4, the output at pin 3 can be brought to the quiescent low level. Thus the reset pin 4 should be held high for normal operation of the IC.

Three sets of switches SA-SC, S1- S8 and S3-S4 are pressed, in that order, to open the lock. On pressing the switches SA and SC simultaneously, capacitor C3 charges through the potential
divider comprising resistors R3 and R4, and on releasing these two switches, capacitor C3 starts discharging through resistor R4. Capacitor C3 and resistor R4 are so selected that it takes about five seconds to fully discharge C3.

Depressing switches S1 and S8 in same time, within five seconds of releasing the switches SA and SC, pulls pin 2 to ground and IC 555 is triggered. The capacitor C1 starts charging through resistor R1. As a result, the output (pin 3) goes high for five seconds.Within these five seconds, switches SA and SC are to be pressed momentarily once again, followed by the depression of last code-switch pair S3-S4.

These switches connect the relay to output pin 3 and the relay is energised.
The contacts of the relay close and the solenoid pulls in the latch (forming part of a lock) and the lock opens. The remaining switches are connected between reset pin 4 and ground. If any one of these switches is pressed, the IC is reset and the output goes to its quiescent low state.

Read More

555-IC Timed Beeper Circuit Diagram

This is a simple timed beeper circuit diagram of beeper using 555 timer. This circuit can be employed to energize lights, horn, or other signaling device at any desired interval when the mercury switch is triggered. Since the current handling capability of mercury switch is not so high, an SCR is used to handle current drawn by the 555 timer circuit. Chose the SCR  current rating of 500mA at minimum to safely drive the 555 IC and the relay. The relay is not needed when the current drawn by alarm is less than 200mA, in this case the alarm can be installed to directly replace the relay coil.  Here is the schematic diagram of the circuit.

555-IC Timed Beeper Circuit Diagram

Read More