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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of

Simple 555 Based Alarm Circuit Diagram

This is a Simple 555 Based Alarm Circuit Diagram.The alarm circuit has a single 555 oscillator/timer (Ul) performing double duty; serving both in the alarm-trigger circuit arid the entry- delay circuit. In this application, the trigger input of IJ1 at pin 2 is held high via Rl. A normally-closed sensor switch, SI, supplies a positive voltage to the junction of R2 and CI, and lights LED1. 

 Simple 555 Based Alarm Circuit Diagram


Simple 555 Based Alarm Circuit Diagram


With both ends of CI tied high, there is no charge on CI. But when SI opens, CI (initially acting as a short) momentarily pulls pin 2 of Ul low, triggering the timed delay circle.At the beginning of the timing cycle, Ul produces a positive voltage at pin 3, which charges C4 to near the positive voltage at pin 3, which charges C4 to near the positive supply voltage.

Transistor Q1 is heavily biased on by R3, keeping its collector at near ground level. With Q1 on, SCRl`s gate is clamped to ground, holding it off. When the delay circuit times out, pin 3 of Ul goes low and ties the positive end of C4 to ground. That turns Q1 off.When Q1 turns off, the voltage at the gate of SCR goes positive, turning on the SCR and sounding the alarm. The delay time is adjustable from just a few seconds (R6 set to its minimum resistance) to about one minute (R6 adjusted to its maximum resistance).

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