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  1. hevans1944

    LM317 question.

    Well, the ATX power supply does provide a well-characterized base from which to start. You can easily add "bells and whistles" externally to suit your purposes. I plan to do just that after I resurrect my home electronics lab after several decades of neglect! I might even purchase a new ATX so I...
  2. hevans1944

    EEG circuit - need help please!

    @eboaylag I would never blindly copy anything on the Instructables web site without fully understanding exactly how and why it is supposed to work... because it probably won't. This site is a fool's-gold mine of misinformation because it is mostly unmoderated in its submissions. Please don't...
  3. hevans1944

    help with voltage reducing, then amplification

    Really? I liked the Dirty Harry movie series, but disagree with the comment about limitations. A man never knows his limitations until he actually runs hard up against them. At which point most of us will try to find a way to get around those limitations. Doesn't always work of course, so we...
  4. hevans1944

    Router Connection

    Connect a relay with a 9V DC coil between point "A" and common. Break the circuit at point "B" and insert normally-closed contacts of the relay. If AC power is available, the relay actuates and its normally-closed contacts will open, removing power provided by the solar array. If AC power is...
  5. hevans1944

    In Memoriam

    Although I can't hold a candle to the light that @KrisBlueNZ cast on this forum, I did appreciate his talent and his efforts helping others here, especially beginners. Kris always took the time to think things out and write clear explanations, providing well-crafted schematics and Bill of...
  6. hevans1944

    Does this part exist?

    Please define the mechanical action you seek for "a latching push to break switch" and a physical size that is acceptable to you. A typical "emergency" off switch can be either a spring-loaded push-button that you press once and release or, (more typically) a plunger-type actuator with two...
  7. hevans1944

    help with voltage reducing, then amplification

    My father served during WWII as a lieutenant and bombardier on B17s. He got shot down during the end of the war bombing Berlin and served the remainder of the war in a German prison camp before being liberated by George Patton's army. I was born while he was still a prisoner, and my brother was...
  8. hevans1944

    help with voltage reducing, then amplification

    @David Stamper Ah! You are conditioning at least three of those little puppies, and it looks like you want to insert the PCBs into a tube, perhaps along with some other electronics, and eventually produce a commercial product. Good job! In which case, the commercial instrumentation amplifiers...
  9. hevans1944

    help with voltage reducing, then amplification

    Aww! How's he gonna learn anything from that?
  10. hevans1944

    help with voltage reducing, then amplification

    It looks like you are getting a good handle on Wheatstone bridge signal conditioning and the use of instrumentation amplifiers. These are really old problems that go back to early in the last century when strain gauges were used to measure stress (change of length per unit length) in structural...
  11. hevans1944

    What is th simplest way to monitor a voltage in a circuit?

    It appears to be there to protect the picaxe A/D input from excessive voltage. My guess is a half-dozen or so series-connected forward-biased diodes would pretty much do the same thing, although the zener should still work too... maybe not as far down on the "knee" as you would like if this were...
  12. hevans1944

    help with voltage reducing, then amplification

    No. The only purpose of the three op-amp circuit is to convert a differential input signal into a single-ended (ground referenced) output signal. The input offset correction is a separate issue. The Texas Instruments paper is a really good introduction to signal conditioning, but there is so...
  13. hevans1944

    help with voltage reducing, then amplification

    You didn't provide the complete part number for this Wheatstone-bridge piezo-resistive absolute pressure transducer. According to the Silicon Microsructures Incorporated datasheet this transducer is available in four full-scale ranges: 15, 30, 60, and 100 psi with 100 mV full-scale output. The...
  14. hevans1944

    PWM circuit with a mind of its own...

    I don't know anything about the open-source Xoscillo code for Arduino (yet), but it appears this would be adequate for troubleshooting. Perhaps you can look at the code and create a loop that samples several things, like the op-amp output and the PWM output, over a period of whatever depth the...
  15. hevans1944

    Need help with a project.. Car radio!

    Well, you know it will take some shielded cables to connect it all up. Making it all work would require a lot more information. Like, what CD player you plan to use, what will it interface with (radio probably) and what your skills are working with automobile wiring, making continuity checks...
  16. hevans1944

    PWM circuit with a mind of its own...

    I had the same thought after I read the datasheet for Microchip's PWM fan controller. It appears to not need anything more than a single NTC thermistor to control a heat-sink fan. Well, that along with four resistors and four by-pass capacitors. See Figure 5-1 Typical Application Circuit on page...
  17. hevans1944

    Need help with a project.. Car radio!

    Oh, some of us here will tackle just about anything if it has some electronics in it... Is that little red button for the nitrous oxide fuel injection or does it pop open a head-light for the chain gun? I am thinking a 3D printer might be what you need to build a compatible-looking facia. Lots...
  18. hevans1944

    PWM circuit with a mind of its own...

    @markcurling Would you go ahead and pencil in the component values and shoot us another photo? I don't see anything wrong with your circuit yet, other than pin 2 is the inverting input (-) of the op-amp and pin 3 is the non-inverting input (+) and you have labeled them backwards. Feedback...
  19. hevans1944

    Creating an LED array in series circuit using PCB

    No kevlar wire needed. Kevlar is non-conductive BTW. I sometimes use kevlar tape for insulation. Just don't push the LED down flush with the board when mounting it, i.e., leave it "proud" above the board. Leave just enough sticking up above the board to allow you to slip a pair of flush-cutting...
  20. hevans1944

    Creating an LED array in series circuit using PCB

    You might want to leave each LED a few millimeters "proud" of the circuit board. That way, if one of them fails, you can just snip it out close to the body and have enough lead sticking up above the board to tack-solder a replacement in place. That's a lot easier than trying to un-solder the...
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