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schultdw

Member Since: June 23, 2006

Country: United States

  • RS-485 is a differential signal so +/-200mV means that the difference between the A and B signals must be greater than 200mV. So the failsafe biasing network that generates >400mV has more than 200mV of margin.

    The article that helped me the most was "The Art and Science of RS-485" by Bob Perrin published by the Circuit Cellar magazine in July 1999. I can usually get Google to turn up a copy of that in pdf form.

  • I don't know what the problem is with the LM358 but the 80's vintage Carver C-1 preamp uses a simple opamp (RC4136) buffer for its headphone output amp. No external push-pull driver.

  • A few points:

    1) Battery noise is so low that they are used when ultra low noise power supplies are required. 2) The opamp PSRR will reject all but fairly high power supply noise levels. 3) While the CMRR spec of the opamp is fair, any mismatch in your gain setting resistors will make it worse. Instrumentation amplifiers (AD623, INA122, etc.) have outstanding CMRR because they are laser trimmed. 4) This sensor looks (electrically) a lot like a moving coil phono cartridge. An amplifier designed for that application (without RIAA eq) might be better. 5) How can the opamp tell the difference between power of: Vcc, 0, -Vcc and 2Vcc, Vcc, 0? (It can't.)

  • The graphic on the board showing the orientation of the x,y,z axis is wrong. I didn't notice this at first but when the Y axis failed I noticed that the x axis didn't respond when I rotated the board around Y. A quick check of the ADXL335 data verified that it is the graphic on the board that is incorrect. It should be rotated 90 degrees so that Y points in the direction X does now.

No public wish lists :(