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A window comparator usually employs 2 comparators with one output indicatingthe input is somewhere between two limits. In these examples, a thirdcomparator is added to display all three conditions where the input is inthe center range, or higher, or lower. The first example uses a thermistor to indicate the temperature is near68 degrees within about +/- 5 degree tollerance. The thermistor measures33K at around 68 degrees and varies about 3570 ohms over a range of 10 degrees.Using a 12 volt supply, the thermistor voltage will be 6 volts in the centerof the range. As the temperature increases 10 degrees, the total resistancefalls 3750 ohms, the current will be 12/ (66K -3750) =193uA and the thermistorvoltage will be 193u * (33k -3750) = 5.65 volts. Temperature Range Indicator Circuit Diagram This represents a voltage change of (6 - 5.65) = 350 millivolts for a 10 degree change. The center resistorof the window voltage divider must then drop 350 millivolts. Using 20K resistorson the top a...

Most of the IR remotes work reliably within a range of 5 metres. The circuit complexity increases if you design the IR transmitter for reliable operation over a longer range, say, 10 metres. To double the range from 5 metres to 10 metres, you need to increase the transmitted power four times. If you wish to real i se a highly directional IR beam (very narrow beam), you can suitably use an IR laser pointer as the IR signal source. The laser pointer is readily available in the market. However, with a very narrow beam from the laser pointer, you have to take extra care, lest a small jerk to the gadget may change the beam orientation and cause loss of contact. Here is a simple circuit that will give you a pretty long range. It uses three infrared transmitting LEDs (IR1 through IR3) in series to increase the radiated power. Further, to increase the directivity and so also the power density, you may assemble the IR LEDs inside the reflector of a torch. For increasing the circuit efficiency,...

A 60-dB Range Compressor circuit shown in the schematic diagram below can produce consistent output of 1.4V P-P over entire 60dB range that is very useful for audio level/volume stabilization.  As the main components, this circuit uses a 741 opamp and JFET. With input range of 20mV to 2oV, this circuit has delay time of 0.4s (decay time)  and response time of 1.2ms (attack time). The JFET is used as  voltage-controlled resistor in peak-detecting control loop of 741 opamp. Here is the schematic diagram of the circuit.  A 60-dB Range Compressor schematic diagram