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In this article I will discuss what switch bounce is and some ways to deal with it. First I will take you through the theory, and later I will show you some ways to handle it in both hardware and in software. Recommended level Beginner Theory What is switch bounce? When you push a button, press a mico switch or flip a toggleswitch, two metal parts come together. For the user, it might seem that the contact is made instantly. That is not quite correct. Inside the switch there are moving parts. When you push the switch, it initially makes contact with the other metal part, but just in a brief split of a microsecond. Then it makes contact a little longer, and then again a little longer. In the end the switch is fully closed. The switch is bouncing between in-contact, and not in-contact. "When the switch is closed, the two contacts actually separate and reconnect, typically 10 to 100 times over a periode of about 1ms." ("The Art of electronics", Horowitz & Hill, Sec...

Basic Of Switch Mode Power Supply In recent years, the use of switch mode power supply (SMPS) has become more comon as more applications demand for greater power eficiency. It makes use of semiconductor (mostly MOSFET) fast switches to switch DC input that has been rectified at high frequency. The advantages of high frequency switching are that it reduces the size of inductor, capacitors & transformer used. Other advantages of switching power supply over linear power supply are : 1) High Efficiency (up to 90% and above for nice design). 2) Output can be higher than input. 3) Able to operate over a variety of input power supply. 4) Able to have over output. The setback of using SMPS compared to linear power supply is that it generates electrical noise which contributes to electromagnetic compatibility design issues & more part count. Buck Converter SMPS The SMPS circuit below from Power Integration makes use of LNK304 as its high frequency switch. Take note that this circuit is...

Half of RL1 and RL2 manipulate the switching and the other is connected to an application. Relays are 200 ohms above ground and at one point are referenced to positive that turns them off. Description: RL1 (which is off) applies plus voltage from its armature and latches RL2 “on”. The application terminals are set to [A]. The condition changes when S1 is activated, voltage is applied to RL2 latching RL1 “on” releasing S1 turns RL2 “off”. RL2’s armature is then directed to R1. Terminals are set to [B]. When S1 is pressed again, the relays negative side are referenced to positive, RL1 turns “off” (there’s no current flow). RL2 turns “on” when S1 is released, terminals are set to [A]. There is slight lag between relays depending on how long S1 is held. Relay Toggle Switch Circuit Diagram Note:  If different relays are used, adjustment of R1’s value may be required. For example, OEG relays (12vdc, 270 ohm coil) need R1 at 60 - 70 ohms. The prime motivation for this design was to avoid ...

Light / Dark Sensitive Switch project is a simple project which operates a relay when the light falling on the LDR goes below or goes above a set point. Input – 12 V @ 50 mA Relay output – SPDT relay 2-in-1 kit, either as light sensitive kit or dark sensitive switch Onboard preset to set the level Power-On LED indicator Relay On LED indicator Power Battery Terminal (PBT) for easy relay output connection Four mounting holes of 3.2 mm each PCB dimensions 50 mm x 54 mm. [ Llink ]

Get the circuit instead of a standard on-off switch. Switching is very gentle. If  we don’t use the PCB, connect unused input pins to an appropriate logic level (‘+’ or ‘-’).  Unused output pins *NEED* be left open!  On the Print Circuit Board this has completed already . One step ’push’ activates the relay, another ‘push’ de-activates the relay. IC1 (the 4069) is a regular Hex-inverter type and is constructed with MOS P-channel and N-channel enhancement mode devices in a single monolithic structure. Alternating On-Off Switch Circuit Diagram : Parts List : R1 = 10K R2 = 100K R3 = 10K R4 = 220 Ohm (optional) C1 = 0.1µF, Ceramic (100nF) C2 = 1µF/16V, Electrolytic D1 = 1N4001 Led1 = Led, 3mm, red (optional) Q1 = 2N4401 (see text) IC1 = 4069, CMOS, Hex Inverter (MC14069UB), or equivalent S1 = Momentary on-switch Ry1 = Relay ) It is going to operate on voltages from 3 to 18 volts, but most applications are in the 5-15 volts.  Although the IC1 4069 contains protection circuitry against...

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 instantenou...