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  1. hevans1944

    Help. No idea what this is.

    Looks like a classroom moving-mirror galvanometer. The lamp housing in the upper right corner shines light onto the small square mirror which reflects the light onto the galvanometer mirror through the circular aperture (which may hold a lens). The light reflected from the mirror on the...
  2. hevans1944

    Rotary Switch

    My Ford factory-installed car radios use a rotary optical encoder only for the volume control, but it somehow "remembers" that last setting when I push it to turn the radio off or on. All other functions, IIRC, are via push-buttons. For tuning I get a choice of scan, search, and a multi-band set...
  3. hevans1944

    Rotary Switch

    @dorke I really like rotary incremental encoder controls. Hardly anything to wear out, silent, good resolution... yada, yada, yada. However, buttons are appropriate for some functions too. My KX3 transceiver is a mixture of both and I wouldn't want to have it any other way. Tuning and menu...
  4. hevans1944

    Rotary Switch

    Yep. Bet he's gonna construct a furnace and zone refine and dope his own silicon transistors too. Or maybe build a particle accelerator and implant ions for a planar structure. Lots of ways to over-engineer this project.:cool:
  5. hevans1944

    Rotary Switch

    You don't need two optical "tracks" to build a rotary optical control. One track of alternating opaque and reflecting (or transparent) segments and two appropriately angular spaced optical sensors (reflective or transmissive) will suffice. One sensor should be adjustable with respect to the...
  6. hevans1944

    Rotary Switch

    Perhaps this 360 degree, continuous rotation, rotary encoder with 20 detent positions AND a push-button will do it for you.
  7. hevans1944

    Voltage Drop across NPN BJT C&E?

    I don't think I was the first person to try this, but it is effective. Since the leads and the moving, as well as the fixed contact, in a reed switch are made of ferromagnetic materials it requires a greater magnetic field externally to close the contacts than it does to maintain the contacts in...
  8. hevans1944

    Can't identify brand

    They are Yurbuds. Available here.
  9. hevans1944

    Voltage Drop across NPN BJT C&E?

    You would still have to use a comparator (or an op-amp connected as a comparator) at the output of the log-amp, unless you ran the log-amp output into an ADC input on the PIC. The log-amp and ADC would then replace the comparator functionality, but with the advantage that four or five decades of...
  10. hevans1944

    Where can I simulate AC circuits?

    What does the LTSpice simulation say, compared to your paper calculations? Do the two node voltages agree? How about the loop currents?
  11. hevans1944

    Where can I simulate AC circuits?

    Use Xc = 1 / jωC and Xl = jωL. Pick a frequency for ω and solve for C and L using the specified reactances on your diagram. Plug the values into the LTSpice program.
  12. hevans1944

    Voltage Drop across NPN BJT C&E?

    I enjoy taking the time to explain things... the Albert Einstein way. At this time I can't do any bench experiments to guide you, but if we close on our "dream home" this month, an electronics workshop setup (even if it has to be in the garage instead of in one of our two "spare" bedrooms or the...
  13. hevans1944

    How to use an accelerometer in a circuit

    Where have you looked? Have you implemented the I²C data link between the accelerometer and your chosen micro-controller? Have you used this data link to program the internal registers of the accelerometer? Verified that the data communications path is working for both send and receive data...
  14. hevans1944

    monte carlo simulation

    Adam, it appears he is designing (and has successfully designed) integrated circuit op-amps and is simulating a new design with HSPICE before committing to silicon. Very old-school, but if you don't already have a design library with recipes, and are doing this from scratch on a new design, it's...
  15. hevans1944

    Voltage Drop across NPN BJT C&E?

    LDRs are inexpensive thick-film devices that can have a lot of variation. A bunch from the same lot will probably track fairly close in resistance versus illumination intensity, but I have seen "grab bag" lots that include a lot of different LDRs. It would be nice to have a circuit that would...
  16. hevans1944

    Driving a 10 watt LED

    There is a resource page on this forum that explains how to drive LEDs. All LEDs require some means to limit the current. LED strip lighting usually has this built into the strip for powering the strip directly from a voltage source. COB LED arrays generally do NOT have current limiting built...
  17. hevans1944

    Voltage Drop across NPN BJT C&E?

    It is. Your comparator works just fine. This thread is discussing how to modulate (switch on and off) the power to conserve coin-cell life. Sorry for the tangent discussion, which I finish below. What a log amp could do is make it easier to set a threshold level for switching between full...
  18. hevans1944

    Voltage Drop across NPN BJT C&E?

    What I do find encouraging is that the engineers and scientists who actually design BJTs, and other semiconductor devices, do know what is going on. However, once the packaged device leaves the fab, it becomes a "black box" and it is open season for all sorts of "explanations" for what is going...
  19. hevans1944

    Voltage Drop across NPN BJT C&E?

    Given a black box, some texts I have read (for beginners) posit a little guy inside the box who turns the wiper arm on a rheostat in response to whatever current is supplied to the input. I am guessing he uses a D'Arsonval current meter, but since the box is sealed and opaque, there is no way...
  20. hevans1944

    Automation seems easy but what am I missing?!?!

    There is a thread here, several years old now, where two Allegro current sensors are used independently to sense motor current in a woodworking shop environment. The circuit accommodates both 220 V AC and 110 V AC power tools simultaneously. When a tool is turned on, the appropriate Allegro...
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