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  1. hevans1944

    Automatic ranging current sensing

    Ha! Since the OP never responded, maybe we can just hijack this thread for our own personal use, or ask a moderator to close it. The sentence I liked from post #1 was this: ROFLMAO! :p Nice LTSPICE model though. :rolleyes:
  2. hevans1944

    Wiper Motor Wiring

    That looks like a brushed DC motor rated for 24 V DC, rotating at 2800 RPM and driving a worm-gear right-angle speed reducer. I have no idea what the 12/24 ratio means. Maybe 12 teeth on the worm and 24 teeth on the output gear? This motor will operate poorly with 12 V DC. Better to use 24 V DC...
  3. hevans1944

    How do constant current loads work and how to make one

    Yeah, Miguel, no way I can compete with off-shore labor.:( I bet someone in Asia can make this for nothing, and make a profit on the volume sold.:p
  4. hevans1944

    Common Cathode Triple digit display pinmap help!!!

    Wow! You have been making progress! Years ago, the pin-outs of LED displays had me stonkered for awhile too... until I finally realized that they HAD to be manufactured in a simple way that connected each segment to each package pin WITHOUT crossing any wires. This was years before anyone was...
  5. hevans1944

    Project Kickoff - Variable Frequency Generator WITH interrupts (gaps)

    I fail to understand the "missing teeth" aspect of the problem. How many teeth are on the gear? How many teeth are missing? What is the pattern (if any) of missing teeth? Every third tooth? Every fifth and sixth tooth? Every other tooth with sometimes more than one tooth missing? A binary...
  6. hevans1944

    Bipolar Junction Transistor Configurations

    Well, experience helps, but if you want to do it right you have to set up a Monte Carlo simulation and vary all the parameters that affect the bias of the BJT. Look at the results and determine what drives the circuit away from "expected" behavior. Don't forget to allow for differences in the...
  7. hevans1944

    Question about wiring computer fans to be used with batteries.

    You could also hard-wire eight "D"-size cells in series and place them in individual loops in an "accessory" belt worn around the waist or over the shoulder like a Mexican ammunition bandoleer. That should allow him to keep "smokin' the baddies" all night long. :cool: .
  8. hevans1944

    op amp

    A pure DC input may be constant, but it DOES have either a positive or a negative polarity with respect to common, as does the op-amp output if the op-amp has a bi-polar (positive and negative power rails) power supply. Clearly, if the input DC is positive and the op-amp has only a positive...
  9. hevans1944

    How do constant current loads work and how to make one

    I bet I could do something for a dollar. My specs, of course.
  10. hevans1944

    Trying to make a transistor cancel another transistor

    Thanks again, @dorke! Good links to lots of free PDF downloads. I LOVE Analog Devices!
  11. hevans1944

    MOSFET Sub-Nanosecond Switching

    The most common avalanche switch is the spark-gap gas switch. These are about as simple as it sounds: a spark gap surrounded by a suitable insulating gas. Once the gas "breaks down" the energy dumped into the spark-gap causes uncontrolled avalanche conduction in the gas until the energy is...
  12. hevans1944

    MOSFET Sub-Nanosecond Switching

    Google is your friend here. Try some of the links on this page. And this early paper might be of some help. Almost all high-speed switching requires some sort of avalanche effect to speed things up into the sub-nanosecond range. The gallium arsenide Photo Conductive Semiconductor Switch or...
  13. hevans1944

    Trying to make a transistor cancel another transistor

    Yes. @dorke, thank you for the link. That goes in my permanent reference file for temperature measuring. It appears to be quite complete and up to date. What was this extracted from? I guess I can Google the authors... Probably in the text book they mention non-contact temperature sensing too...
  14. hevans1944

    Trying to make a transistor cancel another transistor

    @dorke don't blame Chris! See my post #51. NTC thermistors exhibit an exponential inverse relationship, actually. See this ancient papyrus from the 1960s. If you read this paper through to the end you will understand why I never aspired to be a computer programmer. However, everything is linear...
  15. hevans1944

    Trying to make a transistor cancel another transistor

    I hadn't thought of THAT! But in keeping with the analog idea, a digital panel meter is out. So all we need to do is convert the needle deflection into signals that will drive eight LEDs... maybe a tiny mirror glued to the needle to deflect a beam of light onto eight LDRs each wired to turn on...
  16. hevans1944

    Technology Rule

    Yes.
  17. hevans1944

    Dr Who's K9 circuit help...

    The problem with shift registers is ensuring four and only four LEDs from a group of twelve are "randomly" selected. I can't think of a simple way to do that with shift registers, hence the "look up table" approach. I've got several UV-erasable EPROMs pulled from various equipment in the...
  18. hevans1944

    Dr Who's K9 circuit help...

    An old-fashioned EPROM could be programmed with a "pseudo-random" sequence and a simple counter would increment the address. These are (or were) available in various memory "depths" but usually with one byte (eight bits) outputs, so you need two of them to provide twelve outputs with four...
  19. hevans1944

    Newbie help with programmable manual set timer circuits and water pump

    Also make sure you are connecting to the common and the NO (normally open) or NC (normally closed) contacts on the relay, depending on whether you want the pump to operate when the relay is actuated (NO contacts) or when the relay is de-actuated (NC contacts). Nothing will happen if you...
  20. hevans1944

    How do constant current loads work and how to make one

    So, why do you want a "constant current" circuit? What kind of load do you want to attach to it? Do you use any meters or math when you mess around with stuff?:rolleyes: Please tell us what you are trying to DO.
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