Visual AC Mains Voltage Indicator
OBJECTIVE
Wide fluctuations in the AC mains voltage is a very common problem in India. You should not be surprised if some one tells you that the voltage fluctuation could be as much as from 150 volts to 290 volts. Although, majority of our electrical and electronic appliances and gadgets have some kind of voltage stabilization internals built-in, yet more than 90 percent of the faults in these gadgets occur due to these power fluctuations. This simple test gadget can give you real time monitoring of the AC mains voltage in the form of glowing LEDS. It can give you the visible indication of AC mains voltage over a range of 170 volts to 280 volts in steps of 10 volts.
There are 12 LEDS numbered from LED-! to LED-12. For input AC mains voltage of less than 170 volts, all LEDs remain OFF. LED-1 glows when the voltage reaches 180 volts, LED2 glows when the voltage reaches 190 volts. The number of LEDS that glow keeps increasing with every additional 10 volts increase. When the input voltage reaches 280 volts, all the 12 LEDS glow.
CIRCUIT DESCRIPTION
The circuit basically comprises of 12 voltage comparators built around opamp comparator IC type number LM 339. Each of the LM 339 has four comparators inside the IC. One of the inputs of all the comparators (the inverting input) is fed from the unregulated DC output where as the other inputs (the non-inverting inputs) are applied reference DC voltages. Resistors R13 to R25 are so chosen that the reference voltages at points 1 to 12 are respectively 0.933V, 1 .866V, 2.80V,3.732V, 4.665V, 5.598V, 6.531V, 7.464V, 8.397V,9.33V, 10.263V and 11.196V. P1 is so adjusted that when the input voltage is 230VAC the DC voltage at the junction of R26-P1 series combination and R27 is 6.531 volts. All reference voltages have been generated from a regulated voltage of 12 volts. In all these comparators, whenever the voltage at their inverting input exceeds the voltage at their non-inverting input, the LED connected at the output glows.
CONSTRUCTION GUIDELINES
Figs. 21.2 and 21.3 respectively show the PCB layout and components layout.
PARTS LIST
Resistors and Capacitors
R1 to R12 : 100 ohms, 1/4W
R13 to R24 : 1OK, 1/4W
R25 : 8.59K, 1/4W (Use a series combinational 8.2K and 390
ohms instead)
R26 : 15K, 1/4W
R27 : 1OK, 1/4W
P1 :10K Preset
R28 to R39 : 1K, 1/4W
R40 to R51 : 100K, 1/4W
C1 : 100gF, 50V (electrolytic)
C2, C3 : 0.1gF (Ceramic disc)
Semiconductors and ICS
LED-1 to LED-12 : miniature LEDS
Bridge Rectifier,B-1 : Type 1B2 (The bridge can also be made using four rectifier diodes of the type IN 4001) .
VR-1 : Three terminal regulator, type 7812 lC-1 , lC-2, 1C-3 : LM 339
Miscellaneous
Transformer,T-l : Mains transformer: primary 230V Secondary-15V Secondary current-250mA
Fuse : 500mA rating
SW-1 : Mains Power ON/OFF switch Solder metal, Wires etc.
TESTING GUIDELINES
The test procedure has more or less been described during circuit description.
Following steps should however be followed for the calibration of the circuit.
1. Connect the input of the mains transformer to an auto-transformer (VARIAC). Set the auto-transformer voltage at precisely 170 volts. Verify the set voltage with the help of millimeter as the auto-transformer dial may not be properly calibrated.
2. Adjust the resistance of the preset P1 till only LED-! glows. Remember that you have to gradually increase the resistance starting from the minimum and stop increasing it further the moment LED-1 glows.
3. The calibration can be funder checked by increasing auto-transformer voltage beyond 170 volts. Gradually increase the voltage upto 280 volts and observe different LEDS glowing at 10 volt intervals as explained earlier.
Written by David on January 8th, 2010 with
4 comments.
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prince iyke
santosh
#1. February 12th, 2010, at 9:04 AM.
sir,
i’m a b.tech student.we r selected this topic for our mini project.we have project presentation on that.first of all ,thanking for your post.it was very helpful.