Monday, September 1, 2014
Touch Switch using 555 oscillator IC
Sunday, August 31, 2014
Three-Phase Appliance Protector
Many of our
costly appliances require three-phase AC supply for operation. Failure of any
of the phases makes the appliance
Prone to erratic functioning and may even lead to
failure. Hence it is of paramount importance to monitor the availability of the
three-phase supply and switch off the appliance in the event of failure of one
or two phases. The power to the appliance should resume with the availability
of all phases of the supply with certain time delay in order to avoid surges
and momentary fluctuations.
The complete circuit of a three phase appliance
protector is described here. It requires three-phase supply, three 12V relays
and a timer IC NE555 along with 230V coil contactor having four poles. Relays
RL1 and RL2 act as a sensing devices for phases Y and B, respectively.
These relays are connected such that each acts as an enabling
device for the subsequent relay. Therefore the combination of the relays forms
a logical AND gate connected serially. The availability of phase R energizes relay
RL1 and its normally opened (N/O) contacts close to connect phase Y to the
input of transformer X2.
The availability of phase Y energizes relay RL2 and its
N/O contacts close to connect phase B to the input of transformer X3, thus applying
a triggering input to timer IC NE555 (IC1). Therefore the delay timer built around
NE555 triggers only when all the phases (R, Y and B) are available.
It provides a delay of approximately four seconds,
which energizes relay RL3 and its N/O contact, closes to connect the line to
the energizing coil of four-pole contactor relay RL4. Contactor RL4 closes to
ensure the availability of the three-phase supply to the appliance.
The rating of contactor RL4 can be selected according
to the full-load current rating of the appliances. Here the contact current
rating of the four-pole contactor is up to 32A. The availability of phases R, Y
and B is monitored by appropriate LEDs connected across the secondary windings
of transformers X1, X2 and X3, respectively. Hence this circuit does not
require a separate indicator lamp for monitoring the availability of the three
phases. When phase R is available, LED1 glows.
When phase Y is available, LED2 glows. When phase B is
available, LED3 glows. The main advantage of this protector circuit is that it
protects three-phase appliances from failure of any of the mounted on the
backside of cabinet. Connect the appliance through external wires.
Caution. To avoid the risk of electric shock, ensure that AC
mains is disconnected during assembly of the circuit and double check
everything before connecting your circuit to the mains. phases by disconnecting
the power supply through the contactor and automatically restores the three-phase supply to the
appliance (with reasonable time delay) when all the phases are available. Assemble the circuit on a general purpose PCB
and enclose in a cabinet with the relays and contactor.
REMOTE CONTROL FOR HOME APPLIANCES
Connect this circuit to any of your home appliances (lamp, fan, radio, etc) to make the appliance turn on/off from a TV, VCD or DVD remote control. The circuit can be activated from up to 10 meters.
The 38kHz infrared (IR) rays generated by the remote control are received by IR receiver module TSOP1738 of the circuit.
Pin 1 of TSOP1738 is connected to ground, pin 2 is connected to the power supply through resistor R5 and the output is taken from pin 3.
The output signal is amplified by transistor T1 (BC558). The amplified signal is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to Vcc and pin 3 is connected to LED1 (red), which glows to indicate that the appliance is ‘off.’
The output of IC1 is taken from its pin 2. LED2 (green) connected to pin 2 is used to indicate the ‘on’ state of the is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to Vcc and pin 3 is connected to LED1 (red), which glows to indicate that the appliance is ‘off.’ The output of IC1 is taken from its pin 2. LED2 (green) connected to pin 2 is used to indicate the ‘on’ state of the appliance. Transistor T2 (BC548) connected to pin 2 of IC1 drives relay RL1. Diode 1N4007 (D1) acts as a freewheeling diode. The appliance to be controlled is connected between the pole of the relay and neutral terminal of mains.
It gets connected to live terminal of AC mains via normally opened (N/O) contact
when the relay energises.
The 38kHz infrared (IR) rays generated by the remote control are received by IR receiver module TSOP1738 of the circuit.
Pin 1 of TSOP1738 is connected to ground, pin 2 is connected to the power supply through resistor R5 and the output is taken from pin 3.
The output signal is amplified by transistor T1 (BC558). The amplified signal is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to Vcc and pin 3 is connected to LED1 (red), which glows to indicate that the appliance is ‘off.’
The output of IC1 is taken from its pin 2. LED2 (green) connected to pin 2 is used to indicate the ‘on’ state of the is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to Vcc and pin 3 is connected to LED1 (red), which glows to indicate that the appliance is ‘off.’ The output of IC1 is taken from its pin 2. LED2 (green) connected to pin 2 is used to indicate the ‘on’ state of the appliance. Transistor T2 (BC548) connected to pin 2 of IC1 drives relay RL1. Diode 1N4007 (D1) acts as a freewheeling diode. The appliance to be controlled is connected between the pole of the relay and neutral terminal of mains.
It gets connected to live terminal of AC mains via normally opened (N/O) contact
when the relay energises.
