I released an updated version of the Applied Electronics for Bioengineers text today. This draft involved several changes:
- Added modifier for “resistor” at end of Section 5.1
- Changed “load resistor” to “bias resistor” in microphone chapter and lab.
- Fixed microphone schematics to use polarized microphones.
- Figure 11.2 changed to use only one differential channel on PteroDAQ.
- Brief explanation of RMS added to Section 3.2
- Small fixes to Chapters 9–16 and indexing terms added.
- Index cleaned up.
- 60Hz FM figure added to Chapter 14
- Updated power discussion in Sections 0.5, 12.3, 23.1
- Updated to include Teensy 3.2
- Major rewrite of Chapter 23 (Class D power amp)
I’m still not finished with the Class D chapter, but I managed to test today an H-bridge circuit using a 9V power supply, which could provide ±9v signals to a loudspeaker (the full 10W that the loudspeaker can take). I did not actually drive the loudspeaker that far, but I confirmed that the H-bridge was providing the full voltage range for PWM and that I was getting clean signals at the loudspeaker for loudness I was willing to tolerate listening to.
I’m now convinced that an H-bridge design is a simpler approach to teach the students, as well as being more useful for students who go on into the “assistive technology: motor” concentration. Modifying the H-bridge to use logic-level signals from the comparator but high voltages for the power FETs turned out to be quite simple. I just added a small nFET and a couple of resistors to make an inverter with a small voltage swing on the output: