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.
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  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).
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.
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.  

Resistor :
R1= 68 ohm
R2= 1k
R3= 1k
R4=47 ohm
R5= 390 ohm
R6= 390 ohm
Variable Resistor:
VR1= 10k
VR2= 22k
D1= 1N4007
D4= 1N4007
Zener Diode :
ZD1= 10.5V, 0.5W
ZD2= 12V, 1W
LED1= Red light (normal)
LED2= White
LED3= White
C1= 470µF ,
Transistor :
T2= TIP127
IC :
IC1= 7809
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.

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

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).
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

Tuesday, January 4, 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.
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.
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.