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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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Precision Metronome & Pitch generator

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Parts:

R1__________1M  1/4W Resistor
R2_________22K  1/4W Resistor
R3__________6K8 1/4W Resistor
R4__________4K7 1/4W Resistor
R5_________47K  1/4W Resistor
R6________100K  1/4W Resistor
R7_________39K  1/4W Resistor
R8_________12K  1/4W Resistor

C1_________47pF  63V Ceramic Capacitor
C2_______2-22pF  63V Ceramic Trimmer
C3________470pF  63V Ceramic Capacitor
C4_________10pF  63V Ceramic Capacitor
C5________100nF  63V Polyester Capacitor
C6________220nF  63V Polyester Capacitor
C7_________22µF  25V Electrolytic Capacitor

D1-D15___1N4148  75V 150mA Diodes

IC1________4060  14 stage ripple counter and oscillator IC
IC2________4082  Dual 4 input AND gate IC
IC3________4520  Dual binary up-counter IC
IC4________4518  Dual BCD up-counter IC
IC5________4046  Micropower Phase-locked Loop IC
IC6________4040  12 stage ripple counter IC

Q1________BC337  45V 800mA NPN Transistor

XTAL______2.4576 MHz Miniature Quartz crystal

SW1__________BCD Miniature Thumbwheel Switch (units)
SW2__________BCD Miniature Thumbwheel Switch (tens)
SW3__________BCD Miniature Thumbwheel Switch (hundreds)
SW4_________SPST Slider Switch (On-off)
SW5_________SPDT Slider Switch (Metronome-Pitch)

SPKR_______8 Ohm, 50 mm. Loudspeaker

B1_________9V PP3 Battery

Clip for 9V PP3 Battery 
 
 

Circuit operation:

CMos IC1 and IC2B quad AND gate form a 2.4576 MHz crystal oscillator plus a 2400 times divider. IC3A provides further division by 16, delivering a 64 Hz stable frequency square wave. This frequency is multiplied (by means of Phase Locked Loop IC5, double decade divider IC4 and IC3B 4 bit binary divider) by the number set by three miniature BCD thumbwheel switches SW1, SW2 and SW3: units, tens and hundreds respectively.
Connecting, by means of SW5, Q1 base to pin 2 of IC6, we obtain (after a 64 times division) the same frequency set by thumbwheel switches with quartz precision, and no need for a scale indicator.
Volume regulation of the pitch generator is obtained trimming resistor R5. In the same way, with SW5 set to metronome, the small speaker reproduces the frequency set by thumbwheel switches but divided by 3840, thus obtaining beats per minute ratio.