555 timer Mono stable (one shot) circuit

Description 

The two circuits below illustrate using the 555 timer to close a relay for a predetermined amount of time by pressing a momentary N/O push button. The circuit on the left can be used for long time periods where the push button can be pressed and released before the end of the timing period. For shorter periods, a capacitor can be used to isolate the switch so that only the initial switch closure is seen by the timer input and the switch can remain closed for an unlimited period without effecting the output.

In the idle state, the output at pin 3 will be at ground and the relay deactivated. The trigger input (pin 2) is held high by the 100K resistor and both capacitors are discharged. When the button is closed, the 0.1uF cap will charge through the button and the 100K resistor which causes the voltage at pin 2 to move low for a few milliseconds. The falling voltage at pin 2 triggers the 555 and starts the timing cycle. The output at pin 3 immediately moves up to near the supply voltage (about 10.4 volts for a 12 volt supply) and remains at that level until the 22 uF timing capacitor charges to about 2/3 of the supply voltage (about 1 second as shown). Most 12 volt relays will operate at 10.4 volts, if not, the supply voltage could be raised to 13.5 or so to compensate. The 555 output will supply up to 200mA of current, so the relay could be replaced with a small lamp, doorbell, or other load that requires less than 200mA. When the button is released, the 0.1uF capacitor discharges through the 100K and 2K resistors. The diode across the 100K resistor prevents the voltage at pin 2 from rising above the supply voltage when the cap discharges. The 2K resistor in series with the 22uF cap limits the discharge current from pin 7 of the timer. This resistor may not be necessary, but it's a good idea to limit current when discharging capacitors across switch contacts or transistors.
Circuit Diagram

 Source -  http://www.bowdenshobbycircuits.info/page9.htm#555mono.gif

06:15 0 comments

12 Volt Lamp Dimmer Circuit

Description

Here is a 12 volt / 2 amp lamp dimmer that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of a astable 555 timer oscillator. When the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistors and the diode, producing a short positive interval and long negative interval which dims the lamp to near darkness. When the potentiometer wiper is at the lowermost position, the capacitor will charge through both 1K resistors and the 50K potentiometer and discharge through the lower 1K resistor, producing a long positive interval and short negative interval which brightens the lamp to near full intensity. The duty cycle of the 200 Hz square wave can be varied from approximately 5% to 95%. The two circuits below illustrate connecting the lamp to either the positive or negative side of the supply. 

Circuit Diagram

Source- http://www.bowdenshobbycircuits.info/page6.htm#p_input

07:09 0 comments

Alternating Flasher Circuit Diagram

Description

This circuit uses three easily available 555 timer ICs. All three work as astable multivibrators. The first 555 has an on period and off period equal to 1 sec. This IC controls the on/ off periods of the other 2 555s which are used to flash two bulbs through the relay contacts.

The flashing occurs at a rate of 4 flashes per second.

The diodes are used to protect the 555 ICs from peaks. The relays should have an impedance greater than 50ohms i.e, they should not draw a current more than 200mA.

The flashing sequence is as follows:

The bulb(s) connected to the first relay flashes for about 1 sec at a rate of 4 flashes per second. Then the bulb(s) connected to the second relay flashes for 1 sec at a rate of 4 flashes per second. Then the cycle repeats.

The flashing rates can be varied by changing the capacitors C3 and C5. A higher value gives a lower flashing rate.

Note that the values of C3 and C5 should be equal and should be less than that of C1.

The value of C1 controls the change-over rate ( default 1sec). A higher value gives a lower change-over rate.

If you use the normally open contacts of the relay, on bulb will be OFF while other is flashing,and vice versa.

If normally closed contacts are used, one bulb will be ON while the other is flashing.

Circuit Diagram

Source -http://www.electronic-circuits-diagrams.com/lightsimages/lightsckt11.shtml

Designed by Naveen P N

08:11 0 comments

Instant Flash Trigger For Photography Circuit Diagram

 Description

The heart of my flash trigger is an LM555 timer and a DM7473 flip-flop. The 555 provides an adjustable delay between an event being triggered and the flash being fired — for example, we want to wait for a falling drop to fall a few more inches before the flash goes off. The flip-flop triggers at the end of the delay and fires our flash.

A circuit is required that would give a change in voltage when a light beam is interrupted. A phototransistor allows current to flow only when light is present. A large resistor between the phototransistor and ground causes 5V to be output when light is present, but pulls the output to ground when the beam is interrupted.

Unfortunately, there’s bound to be ambient light hitting the phototransistor even when the LED beam is interrupted. The phototransistor may only reduce the voltage at its output by 1V when the beam is interrupted — we normally output 5V, and the 555 timer won’t trigger until the voltage dips below 1.67V, so the change in voltage won’t even be noticed. However, we can divert some of the current from the output of the phototransistor to ground with a variable resistor — this allows us to subtract a constant voltage from the circuit’s output.

Now, instead of GIVING 5V normally, we can divert some current to ground until we’re only GIVING 2V. A 1V drop in voltage will reduce our output to 1V, which is low enough to trigger the 555.

Circuit Diagram 

Since our circuit will use 5V all over the place, our first task is to turn a 9V battery into the voltage we need. Maxim’s MAX603 linear regulator is a handy chip that will output 5V given a wide range of input voltages — with a few supporting capacitors, the chip will do all the work for us. I simply followed the suggested circuit in the datasheet.

Next, I needed a circuit that would output a change in voltage when a light beam is interrupted. for an infrared LED and matching phototransistor. Fairchild Semiconductor has a good application note about designing with phototransistors — essentially, a phototransistor allows current to flow only when light is present. A large resistor between the phototransistor and ground causes 5V to be output when light is present, but pulls the output to ground when the beam is interrupted.

Unfortunately, there’s bound to be ambient light hitting the phototransistor even when the LED beam is interrupted. The phototransistor may only reduce the voltage at its output by 1V when the beam is interrupted — we normally output 5V, and the 555 timer won’t trigger until the voltage dips below 1.67V, so the change in voltage won’t even be noticed. However, we can divert some of the current from the output of the phototransistor to ground with a variable resistor — this allows us to subtract a constant voltage from the circuit’s output.

Now, instead of output 5V normally, we can divert some current to ground until we’re only outputting 2V. A 1V drop in voltage will reduce our output to 1V, which is low enough to trigger the 555.

5 VOLTE POWER SUPPLY MODEL 

 Trigger

Source -  http://www.electronguide.com/circuits_pages/InstantFlashTriggerForPhotography.html

08:41 0 comments

Police siren using NE555

Description.

A lot of electronic circuits using NE555 timer IC are already published here and this is just another one.Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and each of them are wired as astable multivibrators.The circuit can be powered from anything between 6 to 15V DC and is fairly loud.By connecting an additional power amplifier at the output you can further increase the loudness.

IC1 is wired as a slow astable multivibrator operating at around 20Hz @ 50% duty cycle and IC2 is wired as fast astable multivibrator operating at around 600Hz.The output of first astable mutivibrator is connected to the control voltage input (pin5) of IC2. This makes the output of IC2 modulated by the output frequency of IC1, giving a siren effect. In simple words, the output frequency of IC2 is controlled by the output of IC1.

 Circuit diagram.

Notes.

• The circuit can be assembled on a Perf board.
• I used 12V DC for powering the circuit.
• Instead of using two NE55 timer ICs, you can also use a single NE556 timer.
• NE556 is nothing but two NE555 ICs in one package.
• Refer the datasheets of NE555 and NE556 to have a clear idea.
• Speaker can be a 64ohm, 500mW one.

Source - http://www.circuitstoday.com/police-siren-using-ne555

09:58 0 comments

555 LED Flasher

This is a 555 led flasher circuit this circuit will blink many LEDs and give rotating effects. The circuit is very easy to build, 555 timer IC is very common now a days you will find it easily. The circuit uses only 3 volt to perform its task, small 3 volt button cells can also be used and it will last longer because the circuit has low current consumption. Upper 555 IC in the circuit is used as multivibrator and the lower 555 IC is working as a trigger pulse inverter.

 Source http://www.circuitdiagram.org

12:29 0 comments

555 Timer Oscillator

A voltage-controlled oscillator (VCO) using the timer 555 is shown in figure

 555-timer-voltage-controlled-oscillator

 

The circuit is sometimes called a voltage-to-frequency converter because the output frequency can be changed by changing the input voltage.

As discussed in previous blog posts, pin 5 terminal is voltage control terminal and its function is  to control the threshold and trigger levels. Normally, the control voltage is ++2/3V_CC because of the internal voltage divider. However, an external voltage can be applied to this terminal directly or through a pot, as illustrated in figure, and by adjusting the pot, control voltage can be varied. Voltage across the timing capacitor is depicted in figure, which varies between +V_control and ½ V_control. If control voltage is increased, the capacitor takes a longer to charge and discharge; the frequency, therefore, decreases. Thus the fre­quency can be changed by changing the control volt­age. Incidentally, the control voltage may be made available through a pot, or it may be output of a transistor circuit, op-amp, or some other device.

11:04 0 comments

7 Segment Counter Circuit

Seven Segment Counter Display Circuit

Description

Here is the circuit diagram of a seven segment counter based on the counter IC CD 4033.This circuit can be used in conjunction with various circuits where a counter to display the progress  adds some more attraction.

IC NE 555 is wired as an astable multivibrator for triggering the CD 4033.For each pulse the out put of CD 4033 advances by one count.The output of CD 4033 is displayed by the seven segment LED display LT543.Switch S1 is used to initiate the counting.Diode D1 prevents the risk of accidental polarity reversal.

Seven Segment Circuit Diagram with Parts List. 

 Source http://www.circuitstoday.com

11:01 0 comments