Opto-Isolator GW Detector Test

(11-25-1993)
 

A. Test Circuit #OP-1:

Using early Monsanto MCA-230 Darlington unit (also tried MCT-2 device)

B. Remarks:

(1) A set control was used to be able to finely adjust the dc operating point of the LED in the isolator unit. A current-limiting resistance (R_s) of about 150 ohms was used to keep the LED forward current at about 15 mA. The maximum If for this particular unit is about 60 mA, thus at least a 47 ohm R_s should be used. Lower values of R_s (or no R_s) will result in badly degraded LED junctions and thus poor (or no) operation of the unit as a GW detector.

(2) Operation of the LED near the 'knee' of the transfer curve will result in strong l/f and white noise response. When the voltage is reduced below the 'firing point' of about 1.1 volts, there is very little noise developed in the bipolar Darlington junctions!

(3) A Radio Shack Mini Speaker/Amplifier was used in the output.