A bioamp

The AD202 input is equivalent to a one opamp block, with an inverting –input, non inverting +input, and output FB. Together with external dual OPAMP LM358/NJM2904, a classic instrumentation amplifier circuit is formed. A properly built instrumentation amplifier gives the high CMRR performance we wanted, and its gain can be easily adjusted, using only one trimpot for the gain adjustment. To get the best CMRR performance, the resistors used in the circuit must be very closely matched. Hence, 1% precision resistors are used. Actually, even with the use of 1% precision resistor, we can not get the best CMRR the circuit can offer, 1% precision is still too loose. But we have little chance of getting higher precision resistors from our local (Philippines) electronic shops. Nevertheless, even with 1% resistors, the circuit performed respectably, as will be shown in the later part
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