As a follow-up to the simple audio power meter described in [1], the author has developed a more sensitive version. In practice, you rarely use more than 1 watt of audio power in a normal living-room environment. The only time most people use more is at a party when they want to show how loud their stereo system is, in which case peaks of more than 10 W are not uncommon. With this circuit, the dual LED starts to light up green at around 0.1 watt into 8 ohms (0.2 watt into 4 ohms). Naturally, this depends on the specific type of LED that is used. Circuit diagram: Sensitive Audio Power Meter Circuit Diagram Here it is essential to use a low current type. The capacitor is first charged via D1 and then discharged via the green LED. This voltage-doubler effect increases the sensitivity of the circuit. Above a level of 1 watt, the transistor limits the current thr...
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The circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light. Simple Light Sensitive Alarm Circuit Diagram The light-sensitivity of the circuit can be adjusted by varying the 100k preset. The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset. Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on contin...
This is a Simple Touch Sensitive Switch Circuit Diagram . This circuit A high impedance input is provided by Ql, a general purpose field effect transistor 741 op amp is used as a sensitive voltage level switch which in turn operates the current Q2, a medium current PNP bipolar transistor, thereby energizing the relay which can be used to control equipment, alarms, etc. Simple Touch Sensitive Switch Circuit Diagram
The above circuit is a light sensitive automatic switch which functions in the absence of light. We are using IC 4060 in this circuit which works as an oscillator and the generated signal is applied to the base of T4 transistor.Phototransistor T3 is in conduction by existence of light and it keeps the T5 transistor’s base at ground potential. When no light reaches the phototransistor, it gets in insulation. T3 reaches positive potential through 22kohm. T4 and T5 both gets in conductance. The oscillator signal reaches the optic coupler and lamp(s) shines.