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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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Mini Metronome

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Linear scale - Small size

40 to 208 beats per minute

 

Parts:

P1______100K   Linear Potentiometer

R1_______10K   1/2W Trimmer Cermet
R2_______10K   1/4W Resistor
R3______330K   1/4W Resistor
R4_______50K   1/2W Trimmer Cermet
R5______100K   1/4W Resistor
R6,R7_____1K   1/4W Resistor

C1________1µF   63V Polyester Capacitor
C2_______10nF   63V Polyester Capacitor
C3_______47µF   25V Electrolytic Capacitor

IC1_____NE555   General purpose timer IC

Q1,Q2___BC560C  45V 100mA Low noise High gain PNP Transistors
Q3_____ZTX753  100V 2A PNP Transistor

SW1______SPST Switch (Ganged with P1)

SPK______8 Ohm 40mm. Loudspeaker 

B1_____12V Battery (MN21, GP23A or VR22 type) 
 

Notes:

  • Q1 & Q2 provide linear frequency operation of IC1 following P1 resistance variation.
  • Q3 was added in order to obtain a louder click, similar to clockwork metronomes.
  • A 12V micro battery was used to obtain a higher output power and more compactness.
  • Rotate P1 fully towards R2, then set R1 to obtain 40 beats per minute (compare with another metronome).
  • Rotate P1 fully towards R3, then set R4 to obtain 208 beats per minute.
  • Finally mark the entire scale with the usual metronome steps, as follows:
    40 - 42 - 44 - 46 - 48 - 50 - 52 - 54 - 58 - 60 - 63 - 66 - 69 - 72 - 76 - 80 - 84 - 88 - 92 - 96 - 100 - 104 - 108 - 112 - 116 - 120 - 126 - 132 - 138 - 144 - 152 - 160 - 168 - 176 - 184 - 192 - 200 - 208.