Circuit Diagram Knowledge: switch

Showing posts with label switch. Show all posts

Saturday, November 8, 2014

Simple Electronic Quiz Switch

One of the common rounds in the quizzes is the buzzer round. We are describing here a simple electronic circuit that can be used in any test or quiz competition. In this circuit, only four persons can participate, and every participant is assigned a certain number. Whenever a switch is pressed, the circuit locks the remaining three entries. At the same time, an alarm sounds and the designated switch number is displayed on the seven segment LED display.When a player presses his switch, the corresponding output of IC1 goes high. Let us suppose, when switch S1 is pressed, D1 input of IC1 goes low and its corresponding output Q1 goes high. As a result, current passes through D5 to piezo buzzer PZ1, which creates a beep. At the same time, current also passes through diodes D6-D7 to show the number on the LED display.

Circuit diagram:

Simple Electronic Quiz Switch Circuit Diagram

Similarly, when any other switch (S2-S4) is pressed, the corresponding number gets displayed on seven segment displaying DIS1 and buzzer sounds. Switch S5 is used to reset the display exclusively. Switch S5 is a push to on switch. The circuit is powered by 9V battery. Assemble the circuit on a general purpose PCB and enclose it in a suitable case along with seven segment display and piezo buzzer. The assembled circuit can be kept near the host and the switches connected through the external can be assigned to the players.

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Wednesday, November 5, 2014

Cell Phone Controlled Audio Video Mute Switch

This cell-phone-controlled audio/ video mute switch is highly useful in automobiles. The circuit automatically disconnects power supply to the audio/video system whenever the mobile handset is lifted off the holder for making or receiving a call. You can use any readily available cell-phone holder with some mi-nor alterations or fabricate it yourself as shown in Fig. 1.

Fig. 1: Proposed cell-phone holder

The circuit is wired around IC LM555 (IC1), the CMOS version of timer NE555, as shown in Fig. 2. IC1 is used as a medium current line driver with either an inverting or non-inverting output. It can sink (or source) current of up to 50 mA only, so take care while handling it. The audio/video system is connected to the circuit via normally opened (N/O) contacts of the relay.

Fig. 2: The circuit of the cell phone-controlled audio/video mute switch

When the cell phone is in its holder, LDR1 does not receive any light from white LED1 and its resistance is high. As a result, the voltage at pin 2 of IC1 re-mains high to provide a low output at pin 3. The low output of IC1 activates relay RL1 and the audio/video system gets power supply via its N/O contacts. LED3 glows to indicate that the audio/video system is ‘on.’ When the handset is taken off the holder, light rays from LED1 fall on LDR1 and its resistance decreases.

As a result, the voltage at pin 2 of IC1 de-creases to provide a high output at its pin 3. The high output of IC1 deactivates relay RL1 and the audio/video system does not get power supply. LED2 glows to indicate that the audio/video system is ‘off.’ Preset VR1 is used to control the sensitivity of the circuit. Zener diode ZD1 is used for protecting white LED1 from the higher voltage. The circuit works off a 12V car battery. Switch S1 can be used to manually switch on/off the audio/video system.

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Tuesday, November 4, 2014

USB Switch Schematic

Anyone experimenting or developing USB ported peripheral hardware soon be comes irritated by the need to disconnect and connect the plug in order to reestablish communication with the PC. This process is necessary for example each time the peripheral equipment is reset or a new version of the firmware is installed. As well as tiresome it eventually leads to excessive contact wear in the USB connector. The answer is to build this electronic isolator which disconnects the peripheral device at the touch of a button. This is guaranteed to reduce any physical wear and tear and restore calm once again to the workplace.

USB Switch Schematic Circuit Image :
USB

The circuit uses a quad analogue switch type 74HC4066. Two of the switches in the package are used to isolate the data path. The remaining two are used in a classic bistable flip-flop configuration which is normally built using transistors. A power MOSFET switches the power supply current to the USB device. Capacitor C2 ensures that the flip flop always powers-up in a defined state when plugged into the USB socket (‘B’ in the diagram). The peripheral device connected to USB socket ‘A’ will therefore always be ‘not connected’ until pushbutton S2 is pressed. This flips the bistable, turning on both analogue gates in the data lines and switching the MOSFET on. The PC now recognises the USB device. Pressing S1 disconnects the device.

USB Switch Schematic Circuit Diagram :

USB

The circuit does not sequence the connections as a physical USB connector does; the power supply connection strips are slightly longer than the two inner data carrying strips to ensure the peripheral receives power before the data signals are connected. The electronic switch does not suffer from the same contact problems as the physical connector so these measures are not required in the circuit. The simple circuit can quite easily be constructed on a small square of perforated strip-board.

The design uses the 74HC(T)4066 type analogue switch, these have better characteristics compared to the standard 4066 device. The USB switch is suitable for both low-speed (1.5 MBit/ s) and full-speed (12 MBit/s) USB ports applications but the proper ties of the analogue switches and perf-board construction will not support hi-speed (480 MBit/s) USB operation.

The IRFD9024 MOSFET can pass a current of up to 500 mA to the peripheral device with-out any problem.

Source: www.ecircuitslab.com/2012/06/usb-switch-schematic-circuit.html

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Touch Free Timer Switch

This type of infrared proximity circuit is widely used as an electric switch where physical contact is not desired for hygiene purpose. For example, we commonly see use of infrared proximity sensors on public drinking fountains and in public washrooms. The simple circuit presented here can be operated by moving your hand in front of it. This is achieved by detecting the infrared light reflected by your hand onto a receiver device.

Fig. 1: Touch-Free Timer Switch Circuit diagram :

Timer

Fig. 1 shows the circuit of the touch-free timer switch. It has two sections: transmitter and receiver. The IR transmitter is built around timer LMC555 (IC1), which is wired as an astable multivibrator. The multivibrator produces 38kHz pulses (at low duty cycle) that drive an infrared LED (LED1). This frequency can be tuned using a 10-kilo-ohm preset (VR1). A 220-ohm series resistor (R3) ensures that the current consumption of the IR transmitter is not out of arrangement.

The receiver section is built around IR receiver module TSOP1738 (IRX1), timer LMC555 (IC2) and a few discrete components. The TSOP1738 is an integrated miniaturised receiver for infrared remote control systems. Everything required for IR signal processing, including the PIN diode and preamplifier, are assembled on a lead frame and the epoxy package is designed as an IR filter.

When a short IR burst is received by IRX1 (as you wave your hand in front of the switch), the demodulated pulses are fed to the trigger input (pin 2) of the second LMC555 (IC2). This, in turn, triggers the monostable wired around IC2 and its output pin 3 goes high for a period determined by the 2.2-mega-ohm potentiometer and capacitor C5. This turns off the standby indicator (LED1) and transistor T1 conducts to drive the 5V relay (RL1). LED1 enables you to locate the switch in the dark. AC mains supply to the load to be switched-on is routed through the pole and normally-opened contacts of RL1 as shown in the diagram. The circuit works off regulated 5V DC.

Fig. 2: Pin configurations of TSOP1738, IR LED and BC547

Pin

Fig. 2 shows the pin configurations of TSOP1738, IR LED1 and transistor BC547. Assemble the circuit on a general-purpose PCB and enclose in a small plastic cabinet. Fit IR LED1 with a reflecting hood at a recessed position on the front panel of the enclosure. The dome-shaped face of the TSOP1738 should stick out from the front panel. Fit the time-control potentiometer (VR2) in an appropriate position. Finally, fit the standby indicator LED1 inside a suitable LED holder such that it slightly protrudes from the front panel. To prevent unwanted reflection of the IR beam, the finished unit should be mounted such that it does not face a nearby wall.

Fig. 3: Suggested enclosure

Using high-precision linear potentiometer VR2 and capacitor C5 (100µF), the time length can be set from nearly 1 second to 120 seconds. Attach a small paper dial on the front panel of the enclosure and mark various positions of the control knob of VR2 as shown in Fig. 3. The accuracy of the timer depends mainly upon the quality (and value) of timing capacitor C5. In practice, most electrolytic capacitors are rated on the basis of minimum guaranteed value and the real value may be higher.

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Saturday, October 4, 2014

Automatic Lamp switch on

This circuit called the Automatic Lamp switch-on . area the architecture is primarily advised to acquiesce automated switching of lights that will be alive and inactive, depending on ablaze intensity.

On sirki use this photo resistor R1 charge be installed in a box absolute a complete circuit, but charge accomplish a acceptable aperture in the ancillary of the box to acquiesce the ablaze hitting the sensor. Trim R2 move to the adapted absolute is reached. Setup will crave some testing, but should not be difficult. In this circuit, the best accepted and voltage delivered to the lamp(s) are bound mainly by R6 (that can’t be bare if a apple-pie and reliable switching is expected).

Therefore, the Ohm’s Law charge be acclimated to account the best voltage and accepted ethics of the bulbs. At 3V supply, R6 amount can be bargain to 1 or 0.5 Ohm and the operating voltage of the bulbs should be called accordingly, by applying the Ohm’s Law. Stand-by accepted is beneath than 500µA, provided R2 amount afterwards accent is set at about 5K or higher: therefore, the ability about-face SW1 can be omitted. If R2 amount is set beneath 5K the stand-by accepted will access substantially.

Automatic Lamp switch-on Pat List

R1 = Photo resistor
R2 = 22K
R3 = 1K
R4 = 2K7
R5 = 330R
R6 = 1R5
D1 = 1N4148
Q1 = BC547
Q2 = BD438
LP1 = Filament Lamp(s)
B1 = 6V or 3V Battery

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Friday, September 12, 2014

USB Switch Schematic Circuit

Circuit image :

USB Switch Schematic Circuit Image

The schema uses a quad analogue switch type 74HC4066. Two of the switches in the package are used to isolate the data path. The remaining two are used in a classic bistable flip-flop configuration which is normally built using transistors. A power MOSFET switches the power supply current to the USB device. Capacitor C2 ensures that the flip flop always powers-up in a defined state when plugged into the USB socket (‘B’ in the diagram).

The peripheral device connected to USB socket ‘A’ will therefore always be ‘not connected’ until pushbutton S2 is pressed. This flips the bistable, turning on both analogue gates in the data lines and switching the MOSFET on. The PC now recognises the USB device. Pressing S1 disconnects the device.

Circuit diagram :
USB

USB Switch Schematic Circuit Diagram

The schema does not sequence the connections as a physical USB connector does; the power supply connection strips are slightly longer than the two inner data carrying strips to ensure the peripheral receives power before the data signals are connected. The electronic switch does not suffer from the same contact problems as the physical connector so these measures are not required in the schema. The simple schema can quite easily be constructed on a small square of perforated strip-board.

The design uses the 74HC(T)4066 type analogue switch, these have better characteristics compared to the standard 4066 device. The USB switch is suitable for both low-speed (1.5 MBit/ s) and full-speed (12 MBit/s) USB ports applications but the proper ties of the analogue switches and perf-board construction will not support hi-speed (480 MBit/s) USB operation.

The IRFD9024 MOSFET can pass a current of up to 500 mA to the peripheral device with-out any problem.

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Wednesday, August 13, 2014

PCB Exposure Switch Timer V2 0

After some modifications on my UV exposure box (scanner) for better UV expose, i decided that a better pcb must me designed for switch timer. The old one had over drilled holes and it was designed and built on my very fist steps. Also the high voltage side from the low voltage wasn’t separated as it needed to be safe.

So i redesigned it in a more compact and easier to use pcb. The firmware has been also updated and now you can program the timmer by using the two buttons. The time is calculated by timer interrupt triggering using a 32.768KHz RTC Crystal with better accuracy. The display update also has been changed from static to dynamic. [Link]

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Thursday, December 26, 2013

Build a Switch Mode Power Supply

The SMPS described here is suit-able for high-wattage stereos and other similar equipment. The circuit employs two high-voltage power transistors (BU208D) which have built-in re-verse-connected di-odes across their collectors and emitters. It can supply about 250-watt out-put. The circuit uses a ferrite core transformer of 14mm width, 20mm height, and 42mm length of E-E cores. An air gap of 0.5 mm is required between E-E junction. Good insulation using plastic-insulating sheets (Mylar) is to be maintained between each layer of winding.

Switch Mode Power Supply Circuit Diagram

The number of primary turns required is 90 with 26 SWG wire. The secondary winding employs 17 SWG wire (for 4A load current). Each turn of the secondary develops approximately 2 volts. The reader can decide about the output volt-age and the corresponding secondary turns, which would work out to be half the desired secondary voltage. The volt-age rating of capacitors C7 and C8 should be at least twice the secondary output of each secondary section. BY396 rectifier diodes shown on the secondary side can be used for a maximum load current of 3 amperes.

Two feedback windings (L1 and L2) using two turns each of 19 SWG wire are wound on the same core. These windings are connected to transistors T1 and T2 with a phase difference of 180o, as shown by the polarity dots in the figure. First wind the primary winding (90 turns using 26 SWG wire) on the former. Then wind the two feedback windings over the secondary (output). Ensure that each winding is separated by an insulation layer. Two separate heat sinks are to be pro-vided for the two transistors (BU208D).

The filter capacitor for mains should be of at least 47µF, 350V rating. It is better to use a 100µF, 350V capacitor. If the output is short-circuited by less than 8-ohm load, the SMPS would automatically turn off because of the absence of base current. The hfe min (current amplification factor) of BU208D is 2.5. Thus, sufficien base current is required for fully satu rated operation, otherwise the transistors get over-heated. At times, due to use of very high value of capacitors C7 and C8 (say 2200mF or so) on the secondary side or due to low load, the oscillations may cease on the primary side. This can be rectified by increasing the value of capacitor C6 to 0.01mF.

Author : Deepu P.A

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