Fig. 1 Window Comparator using LM358

Looking at Window Comparator Circuits

by Lewis Loflin

The circuit above is what is called a "window comparator." This will out a digital "HIGH" at "X" and a digital "LOW" at pin 2 of the 74LS04 covering a preset voltage range. This 74LS04 can be any inverter or buffer such as a 74LS07 which has an open-collector output.
Looking at the 4N29 or similar opto-coupler, we use this to change the analog voltages on the left side of the circuit to a digital logic level on the right side of the circuit. The output at either pin 1 (X) or pin 2 can drive any number of driver circuits to switch on motors fans, etc.

Just what does a window comparator do?

A conventional voltage comparator circuit is simply OFF or ON. A window comparator is ON in a fixed voltage rage and OFF outside that voltage range.
This circuit uses an Lm358 dual op-amp. This is a single supply device that operates well at 5-volts and comes in a single 8-pin package. In fact the same circuit will work with 12-volt sensors by changing the supply voltage (only) on the left side of the opto-coupler. The potentiometer connected to pins 3 and 6 simulates the voltage output of an analog sensor.
The voltage dividers at pins 2 and 5 set the upper and lower limits for the comparator. As I adjust the potentiometer LED1 will come on when the voltage is between the points set by the HIGH and LOW reference points at pins 2 and 5. Make sure the voltage at pin 2 is higher than pin 5, otherwise the values can be selected.
In fact the two voltage dividers using fixed resistors can be changed to 10K potentiometers for precise adjustment of the "window" of operation.

Fig. 2 Window Comparator using two Lm311s.

In Fig. 2 I used two Lm311 comparators. The circuit operates in the identical manner as Fig. 1 and the opto-coupler section and the two 5K potentiometers will work just fine in Fig. 1.
To test the circuit adjust the HIGH set control (Tp1) to 4-volts and set the LOW set control (Tp3) to 2-volts. Measure Tp2 and the LED will come on from 2 to 4 volts.
In either circuit above LED1 and its resistor can be replaced with Solid State AC Relays with Triacs or an electromechanical relay or contactor.

Simple 12-14 Volt DC to 120 Volt AC Inverter

Simple 12-14 Volt DC to 120 Volt AC Inverter

by Lewis Loflin

The inverter pictured above uses only four resistors and two transistors, and one transformer. While pictured using NPN transistors, PNP transistors could be used as long as one reverses the battery polarity. I have used both the 2N3055 and TIP41A with R1, R2 at 220 ohms. Make sure the transistors are heat sinked.
Note to use this circuit to create 300 volts for flashtubes use a 12-volt center-tapped transformer. See flashtubes.
The key to the voltage output and frequency is the transformer. To get 120 VAC the transformer will have to be 24-volt center-tapped. If using a 12-volt center-tapped transformer the voltage will be over 240 volts at 14 volts DC input.
This operates by the fact the two transistors won't be exactly alike so they switch each other on/off.
The frequency depends on the physical size of the transformer. Smaller transformers operate at a high frequency, large transformers at low frequency. One small transformer I used (9-volt center-tapped) produced over 300 volts at several thousand Hertz. This operated a four foot fluorescent lamp directly with no other parts. The same circuit with a larger (thus lower frequency output) failed to ionize the lamp.
The frequency will also change depending on the load. Be careful because one can really create some dangerous voltages if mishandled.

LG SERVICE CODE SAMPOORNA

Chassis = MC64, MC84, MC84A
MODEL = SAMPOORNA,
RF-14A80K, ADKBBIN, RF-14/ 20/ 21 CB30F, RF- 20/ 21 CB30VE, RF-21FA20KE, CF- 14D79KE, CF- 20/ 21 D79K, CF- 20 /21 F69K, CF-20/ 21S12KE, CF- 20/ 21 D33 KE, CF 20/ 21 S42KS, MC64, MC84, CF- 20/ 21 F60, CF- 20/ 21 F80, CF14/ 20 21 K40E, CF- 14 /20/21 K50/E / X, CF- 14/16/ 20/ 21 S10EX, CF- 14 /16/20/ 21 S12E

ENTERING INTO SERVICE MODE

Simultaneously press ( OK ) button on the remote control handset and front panel of the television receiver , for 6-8 seconds, 

LCD TV INTEGRA 27

Mother board circuit

Speaker 

Front view

Mother board

Smps