Schematic Reference

The series of touch switch or touch switch is built by IC NE555, a series of touch switches can be used to turn on lights, alarms or other electronic equipment.
This circuit uses 2 pieces of metal plate media as touch, MP1 (Metal Plate 1) and MP2 (Metal Plate 2). Touch switch circuit is equipped with a visual LED indicator for relay status (load active). To enable (Relay ON) can be done by touching the surface of MP1 and to turn it off by touching the surface of the MP2. MP1 and MP2 in touch this switch can use a small piece of copper (diameter 5mm) was enough.

Touch Switch series with NE555.

Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts. The relay contacts should be rated above the current requirements for the heater. Temperature changes are detected by a (1.7K @ 70F) thermistor placed in series with a 5K potentiometer which produces about 50 millivolts per degree F at the input of the LM339 voltage comparator. The two 1K resistors connected to pin 7 set the reference voltage at half the supply voltage and the hysteresis range to about 3 degrees or 150 millivolts. The hysteresis range (temperature range where the relay engages and disengages) can be adjusted with the 10K resistor between pins 1 and 7. A higher value will narrow the range.

Electronic Thermostat and Relay Circuit Diagram



In operation, the series resistor is adjusted so that the relay just toggles off at the desired temperature. A three degree drop in temperature should cause the relay to toggle back on and remain on until the temperature again rises to the preset level. The relay action can be reversed so it toggles off at the lower end of the range by reversing the locations of the 5K potentiometer and thermistor. The 5.1 volt zener diode regulates the circuit voltage so that small changes in the 12 volt supply will not effect operation. The voltage across the thermistor should be half the supply or about 2.6 volts when the temperature is within the 3 degree range set by the potentiometer. Most any thermistor can be used, but the resistance should be above 1K ohm at the temperature of interest. The series resistor selected should be about twice the resistance of the thermistor so the adjustment ends up near the center of the control.

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Component value sensitivity is extremely critical, as are temperature coefficients and matching of the components. Best performance is attained when perfectly matched components are used and when the gain of the amplifier is unity.

4.5 Mhz Notch Filter Schematic

To illustrate, the quality factor Q is very high as amplifier gain approaches 1 with all components matched (in fact, theoretically it approaches infinity) but decreases to about 12.5 with the amplifier gain at 0.98.

Differential amplifier is an amplifier that works by amplifying the signal of the difference of the two inputs. Here is a schematic drawing of a simple differential amplifier:

The differential amplifier using components BJT (Bipolar Junction Transistor) which is identical / exactly the same as the amplifier. In the differential amplifier has two input signals (input) the V1 and V2. Under ideal conditions, when both inputs are identical (Vid = 0), then the output VOD = 0. This is because IB1 = IB2 that IC1 = IC2 IE1 = IE2 and. Therefore, the output voltage (VC1 and VC2) cost the same so that VOD = 0.

If there is a difference between the signals V1 and V2, then the Vid = V1 - V2. This will cause the difference between IB1 and IB2. With prices so different from the IC2 IC1, so price increases VOD in accordance with the strengthening of the transistors.

Reinforcement can be used to enlarge the two-level differential amplifier (cascade). Differential amplifier output is connected to the input differential amplifier is the next level. With such a large total gain (Ad) is the product of the first differential amplifier gain (VD1) and the strengthening of the second differential amplifier (Vd2).

In practice, the differential amplifier is preferred if only one output. So that  is use the voltage between the output and earth (ground). To be able to produce an output voltage to earth (ground) is equal to the voltage between the two outputs (VOD), then one of the differential amplifier output of the second level is connecting with an emitter follower (emitter follower).

To obtain better performance, then the output of emitter follower configuration connected by a so-called totem-pole. By using this configuration, the output voltage can swing in a positive X to near VCC and prices can swing in a negative way to approach the price of VEE.