Saturday, January 29, 2011
Small Project of Mini UPS system
This is a simple circuit that’s provides an uninterrupted power supply (UPS) to operate 12V, 9V and 5V DC-powered at up to 1A current. The backup battery takes up the load without spikes or delay when the mains power gets interrupted. It can also be used as a workbench power supply that provides 12V, 9V and 5V operating voltages.
The circuit automatically disconnects the load when the battery voltage reduces to 10.5V to prevent deep discharge of the battery. LED1 indication is provided to show the full charge voltage level of the battery. Miniature white LEDs (LED2 and LED3) are used as emergency lamps during power failure at night.
The circuit automatically disconnects the load when the battery voltage reduces to 10.5V to prevent deep discharge of the battery. LED1 indication is provided to show the full charge voltage level of the battery. Miniature white LEDs (LED2 and LED3) are used as emergency lamps during power failure at night.
step-down transformer provides 12V of AC, which is rectified by diodes D1 and D2. Capacitor C1 provides ripple-free DC to charge the battery and to the remaining circuit.
When the mains power is on, diode D3 gets forward biased to charge the battery. Resistor R1 limits the charging current. Potentiometer VR1 (10k) with transistor T1 acts as the voltage comparator to indicate the voltage level. VR1 is so adjusted that LED1 is in the ‘off’ mode. When the battery is fully charged, LED1 glows indicating a full voltage level of 12V.
When the mains power is on, diode D3 gets forward biased to charge the battery. Resistor R1 limits the charging current. Potentiometer VR1 (10k) with transistor T1 acts as the voltage comparator to indicate the voltage level. VR1 is so adjusted that LED1 is in the ‘off’ mode. When the battery is fully charged, LED1 glows indicating a full voltage level of 12V.
When the mains power fails, diode D3 gets reverse biased and D4 gets forward biased so that the battery can automatically take up the load without any delay.
When the battery voltage or input voltage falls below 10.5V, a cut-off circuit is used to prevent deep discharging of the battery.
Resistor R3, zener diode ZD1 (10.5V) and transistor T2 form the cut-off circuit. When the volt- age level is above 10.5V, transistor T2 conducts and its base becomes negative (as set by R3, VR2 and ZD1).
Resistor R3, zener diode ZD1 (10.5V) and transistor T2 form the cut-off circuit. When the volt- age level is above 10.5V, transistor T2 conducts and its base becomes negative (as set by R3, VR2 and ZD1).
But when the voltage reduces below 10.5V, the zener diode stops conduction and the base voltage of transistor T2 becomes positive. It goes into the ‘cut-off’ mode and prevents the current in the output stage. Preset VR2 (22k) adjusts the voltage below 0.6V to make T2 work if the voltage is above 10.5V.
When power from the mains is available, all output voltages—12V, 9V and 5V—are ready to run the load. On the other hand, when the mains power is down, output voltages can run the load only when the battery is fully charged (as indicated by LED1).
For the partially charged battery, only 9V and 5V are available.
For the partially charged battery, only 9V and 5V are available.
Also, no output is available when the voltage goes below 10.5V. If battery voltage varies between 10.5V and 13V, output at terminal A may also vary between 10.5V and 12V, when the UPS system is in battery mode.
Outputs at points B and C provide 9V and 5V, respectively, through regulator ICs (IC1 and IC2), while output A provides 12V through the zener diode. The emergency lamp uses two ultra-bright white LEDs (LED2 and LED3) with current limiting resistors R5 and R6. The lamp can be manually switched ‘on’ and ‘off’ by S1.
The circuit is assembled on a general-purpose PCB.
There is adequate space between the components to avoid overlapping. heat sinks for transistor T2 and regulator ICs (7809 and 7805) to dissipate heat are used. The positive and negative rails should be strong enough to handle high current. Before connecting the circuit to the battery and transformer, connect it to a variable power supply.
Provide 12V DC and adjust VR1 till LED1 glows. After setting the high voltage level, reduce the voltage to 10.5V and adjust VR2 till the output trips off. After the settings are complete, remove the variable power supply and connect a fully-charged battery to the terminals and see that LED1 is on. After making all the adjustments connect the circuit to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery.
There is adequate space between the components to avoid overlapping. heat sinks for transistor T2 and regulator ICs (7809 and 7805) to dissipate heat are used. The positive and negative rails should be strong enough to handle high current. Before connecting the circuit to the battery and transformer, connect it to a variable power supply.
Provide 12V DC and adjust VR1 till LED1 glows. After setting the high voltage level, reduce the voltage to 10.5V and adjust VR2 till the output trips off. After the settings are complete, remove the variable power supply and connect a fully-charged battery to the terminals and see that LED1 is on. After making all the adjustments connect the circuit to the battery and transformer. The battery used in the circuit is a 12V, 4.5Ah UPS battery.
Resistor :
R1= 68 ohm
R2= 1k
R3= 1k
R4=47 ohm
R5= 390 ohm
R6= 390 ohm
Variable Resistor:
VR1= 10k
VR2= 22k
Diode:
D1= 1N4007
D2=1N4007
D3=1N4007
D4= 1N4007
Zener Diode :
ZD1= 10.5V, 0.5W
ZD2= 12V, 1W
LED:
LED1= Red light (normal)
LED2= White
LED3= White
Capacitor:
C1= 470µF ,
Transistor :
T1=BC548
T2= TIP127
IC :
IC1= 7809
IC2=7805
Transformer = 230V AC 50Hz Output 12V, 1A
Automatic room light controller
This circuit is called the auto circuit which can use any electronic device to operate it automatically. To make this circuit the cost is very low. Any interested student can make it very easily. The main component of this circuit is transistor. Its operation is very easy.
The main purpose of this is to operate a charger fan where need 6volt battery. This circuit is mainly needed when the main power is OFF. That is called load shedding. Because at the time of load shedding , 6volt battery operate the fan automatically. You don’t have need to ON the switch of the fan or OFF the fan switch. Only relay work this as a switch. The charging system is also automatically. On the other big matter is that no over charge is occurred of the battery. So the life time of the battery is increased.
Component:
1. Transistor ( npn ) – 2N2222, BC547
2. Zener Diode - 6.8V
3. Diode
4. Relay - 6V
5. Resistor – 1K, 100Ω
6. Rechargeable Battery - 6V
7. Bulb - 6V
8. Power supply - 6V
Operation:
This circuit is three section, input section and output section. 2N2222 transistor is used to control relay. BC547 transistor is used to control output section using relay. Zener diode and a diode connect with BC547 transistor base as a series connection. Zener diode always controls battery charge. It zener voltage is 6.8V which can’t overcome battery voltage.
When power supply voltage is applied to the 2N2222 transistor base the transistor is on. So the relay is ON relatively the output circuit is OFF. Inverse will occurs when power supply voltage is OFF. When 2N2222 transistor is ON then relay active only battery charging, relay deactivate the fan. Zener diode always keeps battery voltage full (6volt).
Advantages:
1. Need not switch ON/OFF.
2. It depends on AC power supply come or gone.
3. This circuit is used when you are sleeping.
4. Easy to make
5. Cost is very low
6. Components are few.
7. Battery can’t over charge.
8. Overall efficiency is 78%.
9. Not you, only relay can do your work.
10. The circuit is a small project for all students.
Saturday, January 22, 2011
Color Sensor Circuit Diagram
This is a color sensor Circuit Diagram. This circuit will sense 8 colors that are: , green, red and blue ; magenta, cyan and yellow ; and black and white. It’s will be very useful for robotics project. The object whose colour is required to be detected should be placed in front of the system. The light rays reflected from the object will fall on the three convex lenses which are fixed in front of the three LDRs. The convex lenses are used to converge light rays. This helps to increase the sensitivity of LDRs. Blue, green and red glass plates (filters) are fixed in front of LDR1, LDR2 and LDR3 respectively. When reflected light rays from the object fall on the gadget, the coloured filter glass plates determine which of the LDRs would get triggered.
The circuit makes use of only Op-amp IC..
When a primary coloured light ray falls on the system, the glass plate corresponding to that primary colour will allow that specific light to pass through. But the other two glass plates will not allow any light to pass through. Thus only one LDR will get triggered and the gate output corresponding to that LDR will become logic 1 to indicate which colour it is.
Similarly, when a secondary coloured light ray falls on the system, the two primary glass plates corres- ponding to the mixed color will allow that light to pass through while the remaining one will not allow any light ray to pass through it. As a result two of the LDRs get triggered and the gate output corresponding to these will become logic 1 and indicate which color it is.
When all the LDRs get triggered or remain untriggered, you will observe white and black light indications respectively. Following points may be carefully noted :
1. Potmeters VR1, VR2 and VR3 may be used to adjust the sensitivity of the LDRs.
2. Common ends of the LDRs should be connected to positive supply.
3. Use good quality light filters.
The LDR is mounded in a tube, behind a lens, and aimed at the object. The coloured glass filter should be fixed in front of the LDR as shown in the figure. Make three of that kind and fix them in a suitable case. Adjustments are critical and the gadget performance would depend upon its proper fabrication and use of correct filters as well as light conditions
Monday, January 3, 2011
Automatic Water Level Circuit.
The circuit is based on a 555 IC for sensing the minimum and maximum water levels and turns a MOSFET on/off which directly controls a 12V DC pump motor.
Circuit Diagram:
Here we are using the ‘Trigger’ and ‘Threshold’ pins (2 & 6) to detect the maximum and minimum levels, respectively. The two voltage comparator op-amps inside the 555 control the output, turning it on/off.
Looking at the circuit diagram you will notice that the ‘Trigger’ pin (2) is marked ‘HIGH probe’, despite being triggered (output goes HIGH) when the voltage drops below 1/3 of the supply voltage and, the ‘Threshold’ pin (6) is marked ‘LOW probe’ while it is ‘reset’ (output goes LOW) when the voltage rises above 2/3 of the supply voltage. If this appears to you as being upside-down.
Circuit Diagram:
The circuit works as follows:
Three (3) probes are immersed in the vessel. (usually from the top)
One is the ‘GROUND’ probe, going to the level a little lower than the minimum desired level. This is the ‘common’ (or ‘reference’) probe. The LOW and HIGH probes are set at the desired levels.
One is the ‘GROUND’ probe, going to the level a little lower than the minimum desired level. This is the ‘common’ (or ‘reference’) probe. The LOW and HIGH probes are set at the desired levels.
Now suppose the vessel is EMPTY.
Resistors R2 and R1 (1M) tie the ‘Trigger’ and ‘Threshold’ pins (2 & 6) to the positive (+) rail (supply). In other words, both pins are HIGH. Remember (from above), to make the output of IC1 go HIGH, the trigger pin (2) needs to drop below 1/3 of the supply voltage. (4V with a 12V supply) Since the trigger pin is still HIGH, the output remains LOW.
We need to fill the vessel when IC1’s output is LOW.
TR1 is OFF. The GATE of the MOSFET switch (TR2) is connected to the supply rail (+12V) with R4 (10k).
TR2 is thus turned on and the pump motor is running.
TR1 (BC547) is connected between the IC1s output (pin 3) and the TR2’s GATE.
Its purpose is phase reversal. It means that when IC1’s output is HIGH, TR1 conducts and pulls its collector/TR2’s GATE junction LOW, so TR2 is OFF. Since the pump (or relay coil) is connected between the positive rail (+12V) and TR2’s DRAIN, the pump/relay coil is NOT energized.
Its purpose is phase reversal. It means that when IC1’s output is HIGH, TR1 conducts and pulls its collector/TR2’s GATE junction LOW, so TR2 is OFF. Since the pump (or relay coil) is connected between the positive rail (+12V) and TR2’s DRAIN, the pump/relay coil is NOT energized.
Now, back to the condition when the IC1’s output is low, TR2’s GATE is HIGH (+12V) and conducting. The pump is operating and water is being filled. As the water level rises, a water ‘bridge’ is formed between the GROUND (common) probe and the ‘LOW probe’ (Threshold, pin 6) This ‘bridge’ constitutes a low resistance, relative to the high resistance of R2 (1M), bringing the voltage at this pin to a low level (at least below 1/3 supply but actual voltage depend on the conductivity of the water). However, this is IGNORED by IC1 since its output is already LOW (in the ‘reset’ mode)
When the water level reaches the ‘HIGH probe’, a water ‘bridge’ is formed between it and the GROUND probe. Just as with the LOW probe, this ‘bridge’ constitutes a low resistance, relative to the high value of R1 (1M), bringing the trigger voltage to below the required level (1/3 supply voltage) and IC1 triggers, its output going HIGH. Now Tr1 is turned on, the bias voltage/current of TR2 is removed and the pump STOPS. The filling cycle is completed.
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