InstruAmp

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Custom Module:
InstruAmp
Author Adrián Bulnes, aka Urriellu
Type Sensor
Style Perfboard
Complexity Easy


This is a very simple instrumentation amplifier that takes a differential input signal and amplifies it with high accuracy. Its output is a standard data connector, intended to be plugged to a Main Board.

Electronic circuit

Bill of materials:

  • Perforated board of at least 5x6 holes. Individual pads, not copper strips
  • 1x AD620AN instrumentation amplifier
  • 1x 8-pin PDIP socket
  • 1x 51Ω 1/4W resistor
  • 5x Straight male headers (usually sold as 40-pin strips)
  • You also need two electrodes or probes which provide the differential voltage being amplified


Schematic
Layout: top view
Layout: bottom view


How it works

Two electrodes, probes, or any other kind of voltage source are connected to the inputs (see P2 on the schematic). The voltage differential between these inputs is then amplified by a given gain factor. This gain is determined by resistor R1.

The required value of R1 for a given gain factor can be calculated using the formula provided by the AD620AN datasheet. In this example I used a 51Ω resistor which provides an approximate gain of 1000.

The amplified output voltage is connected to a Main Board using a standard data connector. The range of possible voltage values available at pin 1, the data pin, is more or less the same as the power supply range. This Module is powered directly from the Main Board, usually at 5V, and the amplifier's -Vcc is connected to ground. This means that if the entire circuit (including this Module) is powered at 5V, then the output voltages can only be set between 0V and a bit less than 5V.

By default, this is the same range at which microcontroller's analog-to-digital converters work. Due to that, this Module has been designed to amplify small positive voltages to a range which can be read with more accuracy by the microcontroller.

Pictures

Instrumentation amplifier module Instrumentation amplifier module Instrumentation amplifier module Instrumentation amplifier module Instrumentation amplifier module


Test

For testing this module you can use the Electrooculograph source code.

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