TREE

Reagarding this circuit sent out an alarm when its LDR sensor is exposed to light by sun or lamp. A 555 astable multivibrator was used here which sent signal a tone of about 1kHz upon detecting light. The sensor when exposed by light completes the circuit and makes the 555 oscillate at about 1kHz with transistor to drive current. The sensor is also shown in the circuit diagram. It has to placed making an angle of about 30 – 45 degrees to the ground.  Sensitivity can be adjust with P1.  This makes the sun light to flow through it to the ground and prevents the alarm from going on due to the stored light on the sensor.

In many circuits we need to generate an internal adjustable voltage. This circuit shows how it is possible to use a trusty old NE555 timer IC and a bit of external circuitry to create a voltage inverter and doubler. The input voltage to be doubled is fed in at connector K1. To generate the stepped-up output at connector K2 the timer IC drives a two-stage inverting charge pump circuit. The NE555 is configured as an astable multivibrator and produces a rectangular wave at its output, with variable mark-space ratio and variable frequency. This results in timing capacitor C3 (see circuit diagram) being alternately charged and discharged; the voltage at pin 2 (THR) of the NE555 swings between one-third of the supply voltage and two-thirds of the supply voltage.  Voltage Inverter Circuit Using IC NE555 The output of the NE555 is connected to two voltage inverters. The first inverter comprises C1, C2, D1 and D2. These components convert the rectangular wave signal into a nega...