Posts Tagged ‘circuit switches’

The best electronic switch

This switches circuit,It can be useful many things.which a output of the circuit can be controlled a bell or other sound source circuit or control relay or SCR.(a circuit for RY1,and SCR2 are used with AC voltage source only) The contact switches (S1, S2 and S3) in the parallel circuit,it were used to control a connect switched circuit, which can usefully for a burglar alarm circuit or control alarm signal.
The two transistors work as switches that are highly uncertain,and do not trigger an error,because no other noise.The conduction of the SCR2 was very stable, because the resistance 1K as parallel to the relay.When the trigger and press the switch S2, which is normally closed for the circuit breaker. To relay to stop working. The LED1 to visit the emitter pin of the transistor Q2, it lights up when the Circuit works.

On And Off Button

In this simple circuit we give the chip a little more attention than usual. It is astonishing what can be built with a 555. We are always infatuated with simple circuits using this IC, such as the one shown here. The 555 is used here so that a single push-button can operate a relay. If you press the button once, the relay is energized. When you press it again the relay turns off. In addition, it is possible to define the initial state of the relay when the power supply is switched on. The design is, as previously mentioned, very simple. Using R1 and R2, the threshold and trigger inputs are held at half the power supply voltage.
When the voltage at the threshold pin becomes greater that 2/3 of the power supply voltage, the output will go low. The output goes high when the voltage at the trigger input is less than 1/3 of the power supply voltage. Because C2, via R3, will eventually have the same level as the output, the output will toggle whenever the push-button is pressed. If, for example, the output is low, the level of the trigger input will also become low and the output will go high! C1 defines the initial state of the relay when the power is applied. If the free end of C1 is connected to Vcc, then the output is high after power up; the output is low when C1 is connected to ground.
Author: Ger Langezaal – Copyright: Elektor Electronics
Read more:http://www.extremecircuits.net/2010/06/on-and-off-button.html

Push Off Push On

The ubiquitous 555 has yet another airing with this bistable using a simple push-button to provide a push-on, push-off action. It uses the same principle of the stored charge in a capacitor taking a Schmitt trigger through its dead-band. Whereas the Schmitt trigger in that reference was made from discrete components, the in-built dead-band arising from the two comparators, resistor chain and bistable within the 555 is used instead. The circuit demonstrates a stand-by switch, the state of which is indicated by illumination of either an orange or red LED, exclusively driven by the bipolar output of pin 3. Open-collector output (pin 7) pulls-in a 100-mA relay to drive the application circuit; obviously if an ON status LED is provided elsewhere, then the relay, two LEDs and two resistors can be omitted, with pin 3 being used to drive the application circuit, either directly or via a transistor.
The original NE555 (non-CMOS) can source or sink 200 mA from / into pin 3. Component values are not critical; the ‘dead-band’ at input pins 2 and 6 is between 1/3 and 2/3 of the supply voltage. When the pushbutton is open-circuit, the input is clamped within this zone (at half the supply voltage) by two equal-value resistors, Rb. To prevent the circuit powering-up into an unknown condition, a power-up reset may be applied with a resistor from supply to pin 4 and capacitor to ground. A capacitor and high-value resistor (Rt) provide a memory of the output state just prior to pushing the button and creates a dead time, during which button contact bounce will not cause any further change. When the button is pressed, the stored charge is sufficient to flip the output to the opposite state before the charge is dissipated and clamped back into the neutral zone by resistors Rb. A minimum of 0.1 µF will work, but it is safer to allow for button contact-bounce or hand tremble; 10 µF with 220 k gives approximately a 2-second response.
Author: Trevor Skeggs – Copyright: Elektor July-August 2004
Read more : http://www.extremecircuits.net/2010/06/push-off-push-on_20.html