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Wednesday, September 29, 2010

Vibration Sensor/Detector

With the help of a simple ceramic piezo-electric detector it is possible to assemble an interesting and useful Impact sensor unit,which can be used to detect impact and vibration on doors, showcases, windows etc. The shock sensor (Ceramic piezo-electric detector) uses a “unimorph” diaphram, which consists of a piezo-electric ceramic disk laminated to a metal disk. 

The sensor supplies a voltage proportional to the acceleration of the impact or vibration, for example 40mV/G ie output is near 2V for 60G impact.Here a low voltage, low current Impact sensor unit is realised using a standard ceramic piezo-electric detector which drives a monostable multivibrator (IC1) circuit to activate a npn silicon transistor (T1). Open collector output of this transistor switch can be interfaced to an external alarm/switch circuit for further processing. Since current consumption of the circuit is very low (from 5 to 6 mA only) any common 3V button cell can be used to power the sensor unit.When an impact is sensed, the monostable drives the transistor switch to ON , for a finite duration determined by the incircuit values of RC timing components R3 and C2.

The M74HC123 (IC1) is an high speed DUAL retriggerable CMOS MONOSTABLE MULTIVIBRATOR (MMV) fabricated with silicon gate C2MOS technology, with all inputs protected against static discharge and transient excess voltage. There are two trigger inputs, negative edge and positive edge. Here, only one monostable part with positive edge triggering (pin 2) is used. After triggering, the output maintains the monostable state for the time period determined by the external resistor R3 and capacitor C2.

7805 Regulator IC Circuits


Fixed voltage Positive and Negative regulator ICs are used in circuits to give precise regulated voltage.78 XX series regulator IC can handle maximum 1 ampere current. The Regulator ICs require minimum 1.5 higher input voltage than their voltage rating. For example 7805 IC requires minimum 6.5 volts to give 5 volt output. Here are some circuit designs of IC 7805 to monitor the output voltage.
1.This is the manipulation of the Regulator IC 7805 to give 9 volt regulated output. Normally the pin2 of the regulator IC is connected to the ground. Here it is connected to a 3.9 volt Zener diode. So the output from the Regulator IC will be 9 volts. 

2. This circuit can tell whether the IC 7805 is giving output or not. IC 7805 requires minimum 6.5 volt input to give 5 volt regulated output. When the input voltage is above 6.5 volts, Zener conducts and LED turns on indicating sufficient input voltage. Diffuse type Red LED requires 1.8 volts and Zener 4.7 volts .So to activate both these, input voltage should be minimum 6.5 volts. If the input voltage drops below 6.5 volts, Zener cutoff and LED turns off. This indicates the zero output from the regulator IC.
 3. This is a simple LED monitor to tell the output voltage from 7805. If the input voltage is above 6.5 volts, LED shows full brightness. When the input voltage reduces below 6.5 volts, brightness of LED decreases.