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

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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
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CAR TACHOMETER

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A 555 is configured as a monostable or one shot in this project. The period
of the 555 is determined by the 47k and the capacitor from pin 6 to ground
(100n). Time "T" = 1.1 RC or 1.1 X 50,000 X 0.1 X10 -6 = 0.0055 or 5.5
mS (milli-seconds).
The 555 receives trigger pulses from the distributor points. These are
limited by the 1k and 5v zener diode. These are AC coupled to the trigger
input through the 100n coupling capacitor. The 50mA meter receives
pulses of current through the 200k pot to show a reading.
Integration of the current pulses produces a visible indication of the cars
engine speed on the 0-1mA meter.
Supply is taken from the cars 12v system and for the 555 it is reduced to a
regulated 9v by the 15 ohm resistor in conjunction with the 9v zener diode.
Note: the 10u electrolytic must be placed physically as close as possible
to supply pin 8.