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  1. hevans1944

    Confused points. The Skin Effect, and attenuation.

    Inductance and capacitance have nothing at all to do with skin effect, which is caused by opposing eddy currents flowing in the conductor. Distributed inductance and capacitance affect the impedance of a wire considered as a transmission line.
  2. hevans1944

    isolation problem

    The OP didn't mention what the "monitoring equipmnt" actually was, implying however that several things were monitored and only this one thing was giving problems. Anyway, in lieu of further comments from the OP, I think we are done here. I know I am.
  3. hevans1944

    Project Problems! Need guidance.

    Wow! What a can of worms we have opened up here! The first problem you need to solve is the non-linear performance of the transmitter circuit following the CMOS MUX, caused by the 11X gain stage going into saturation. As I mentioned in post #13 you MUST lower the gain so the amplified pulse...
  4. hevans1944

    isolation problem

    Are you sure about your "relay" part number: Crydom CX240d5? See datasheet here. This is a solid-state "relay". No moving parts, but it operates only to switch an AC load from up to 240 VAC line. It uses back-to-back SCRs as power line switches. Current through an SCR must go to zero before it...
  5. hevans1944

    Project Problems! Need guidance.

    Changing the capacitor value will indeed affect the resonance frequency, f = 1 / (2pi√(LC)). For the values you listed (0.47 μF and 135 μH) resonance occurs at about 19,980 Hz. Close enough to 20 kHz, but small variations in frequency around the resonant tank frequency can have a large effect on...
  6. hevans1944

    Project Problems! Need guidance.

    Yeah, post a schematic with labeled components (so we can make specific comments) and pictures are always appreciated. For specialty parts (the transducers maybe?) identify by manufacturer and model or part number. Is your tank circuit 470 nF capacitor resonant with the 135 μH inductor at the...
  7. hevans1944

    How to power an LED, NEED CLARITY.

    Don't follow my advice or the advice of anyone else blindly. Understand the circuit and check the math. My advice in post #13 was incorrect. The LM317T will not be operating within its specifications if you try to drive an LED with 16.2 V forward voltage at 0.3 A. It will work within specs if...
  8. hevans1944

    How to power an LED, NEED CLARITY.

    @(*steve*): Thanks for noticing. I guess I got a little long-winded and somewhat off-track there. All @Ivin needed to hear from me was in the last two paragraphs of post #13. I will wait for further questions from the OP before posting to this thread again. You are absolutely right about LED...
  9. hevans1944

    How to power an LED, NEED CLARITY.

    @Bluejets is a radio-controlled (RC) model enthusiast. It is understandable that he has extreme disregard for either dropping resistors or linear regulators. @Bluejets is absolutely correct that either one wastes power and produces heat. In a model airplane extra weight is a performance killer...
  10. hevans1944

    How to power an LED, NEED CLARITY.

    From inspection of the pdf datasheet at high magnification for the OD-669-850 HIGH-POWER GaAlAs IRED ILLUMINATOR it is apparent that the device consists of nine series-connected LED "chips" in a 3x3 array. The series wire connections are clearly visible. There is no internal regulator, which can...
  11. hevans1944

    How to power an LED, NEED CLARITY.

    An LED operates as a forward-biased diode. The current through an LED is therefore a quadratically increasing function of the voltage. That means small changes in the forward voltage drop are produced by relatively large changes in the forward current. For this reason (among others) an LED works...
  12. hevans1944

    Fail-safe shaft rotation sensor

    Another "oops". The SN74LS121N is NOT re-triggerable. The dual monostables SN74LS122N and SN74LS123N are both active and re-triggerable, so I should be able to purchase either on-line from a distributor. After lots of surfing on the Internet the past few day I discovered this is an old problem...
  13. hevans1944

    Fail-safe shaft rotation sensor

    Oops again. The 555 is not capable of re-triggering to extend the timing interval unless additional circuitry is added to discharge the timing capacitor without affecting the state of the internal flip-flop. I am looking into this and setting up a breadboard trial. However, a Texas Instruments...
  14. hevans1944

    Fail-safe shaft rotation sensor

    Thank you, Harold Kapp, for pointing out the obvious. Retriggering, NOT resetting, the monostable is the obvious solution. No need for an additional flip-flop. The 555 output can directly drive the fail-safe relay coil, with the same race caveat that I noted in my original post. I will try to...
  15. hevans1944

    Fail-safe shaft rotation sensor

    I have a shaft-mounted cast iron pulley with six spokes that is motor-driven with a v-belt. A Cherry GS100701 gear rotation sensor with an internal permanent magnet is mounted in a position to sense the passage of each iron spoke past the sensor head when the pulley is turning. I need a circuit...
  16. hevans1944

    Designing a Time Delayed Relay

    There are commercially available products that do what you want to do. The inductive sensor relay contacts are connected to operate a 110 VAC delay-on-release relay, also a commercial product. The delay-on-release relay closes its normally-open contacts as soon as it is energized by the...
  17. hevans1944

    Wireless Power Transmission help!

    I know virtually nothing about the currently popular near-field coupling of high-frequency power, presumably to re-charge portable devices such as cell phones and tablets. I am hoping my next smartphone has this feature because the micro-USB connector/jack used to (mainly) re-charge my Samsung...
  18. hevans1944

    resistance monitor

    Thank you, KrisBlueNZ! Nicely engineered solution.
  19. hevans1944

    PCB Software

    Nice layout. Is this one of those voltage-to-LED bar-graph display thingys? Another poster here needs one to monitor the position his truck suspension.
  20. hevans1944

    resistance monitor

    Okay, the switch and resistor are connected with a 10m cable to something whose function changes when the circuit changes from switch activated (closed) to switch deactivated (open) and a 8k2 value resistor is placed in series with the two-wire cable. So, what is on the other end of that cable...
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