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  1. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    If you connect the LED anode to Vcc, and the cathode to the 555 output through the current limiting, then the LED is driven by the 555 low output, not its high output. The low output has no minimum duty cycle percentage. It is set by Rb only, so it will remain fixed as Ra is adjusted to match...
  2. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    Why? ak
  3. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    If you dill in more details about the LED. it can be done with one 555. Available voltage to run the circuit Vf of the LED Desired LED current Does the LED have to be tied to either Vcc or GND ak
  4. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    So - and I'm just GUESSING here: 1. There is some kind of sensor that is tripped or triggered 20 times per revolution of something, and you want to flash one LED (voltage? current? power?) with each sensor activation - ? 2. There is no sensor. You want a free-running astable oscillator to...
  5. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    That does me absolutely no good. I don't. ak
  6. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    Flash all 20 LEDs together, or one at a time as they pass some reference point? ak
  7. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    Still not clear. Are you looking for a circuit that senses when each piece goes by? Or one that takes an input from a sensor and flashes an LED? Or a free-running oscillator to flash the LEDs that is times such that is is synchronized to the rotation? Still not clear. Is the 555 circuit...
  8. AnalogKid

    Having trouble making a 555 timer circuit for a 0.5ms LED flash...

    Please post your schematic. "Engineers don't take a dump, son, without a schematic." Be sure to include a reference designator and part value for each component. A common way of getting better adjustability is to use a fixed resistor in series with a variable one. For example, if...
  9. AnalogKid

    Alarm...ish Covid vaccin

    You guess? Isn't that your schematic? ak
  10. AnalogKid

    Alarm...ish Covid vaccin

    Then I misunderstood your original post. I thought "MUST BE" meant you were required to use at least one of every component on the list. What is the purpose of L1 in your schematic? ak
  11. AnalogKid

    Alarm...ish Covid vaccin

    As bertus said, window comparator. The directions seem to force you to use parts not strictly necessary. For example, I can see using a BJT or MOSFET, but don't know why the instructor thinks it is important to use both. ak
  12. AnalogKid

    Cell phone detector circuit

    The text in the post #6 link explains the circuit in post #1. C2 and its lead inductances form a parallel resonant network, and the opamp is a current-to-voltage converter and, effectively, a half-wave rectifier. I'm still struggling with an LM358 amplifying a 9.0-to- 2.4 GHz signal, but it...
  13. AnalogKid

    Cell phone detector circuit

    Please post a link to the source of the circuit. As shown it will not do anything. Assuming that ANT.1 is an RF signal, that signal will be shunted to the power ground by C1 and shunted to the circuit reference by C2. The output at pin 1 will sit at approx 1.5 V. The voltage across the LED...
  14. AnalogKid

    Hello, Where Does this 2V difference come from in Op-Amps

    Of course not - that would be waaaay too easy. Some newer opamp designs are called "rail-to-rail". At low output currents, the output stage can swing very close to the rails, sometimes within 0.1 V. But most of the standard garden-variety opamps people think of need at least 1 V of working...
  15. AnalogKid

    Hello, Where Does this 2V difference come from in Op-Amps

    I'm not familiar with this simulation program, nor its library structure and model complexity level. But ... It could be that the opamp model has +/-2 V of headroom built into its output characteristics to more accurately simulate real-world devices. It is common for an opamp's output stage...
  16. AnalogKid

    Automatic links

    Speak for yourself. ak
  17. AnalogKid

    Waterproof low voltage circuit needed

    First pass at a latching window comparator with reset. U1A and B form the window comparator. The output is high only if the input is between the two trip points. Note that the high trip point voltage is used as the reference for the two following stages. Those stages need anything between 1...
  18. AnalogKid

    Waterproof low voltage circuit needed

    The circuit is called a window comparator. Typically this is done with two comparators, such as the two halves of an LM393. One senses that the input is below the upper limit, and the other senses that it is above the lower limit. These drive a small transistor that drives the LED. How...
  19. AnalogKid

    Waterproof low voltage circuit needed

    Link to the sensor? Your voltage level descriptions are not clear. To us, +/- 4 V is the way to describe a sine wave or some other periodic signal that goes both above and below GND. I'm guessing you mean that the OK signal is approx 4 V or more above GND, and the Tilt signal is 1 V or less...
  20. AnalogKid

    Waterproof low voltage circuit needed

    The circuit is called a flipflop, which is a 1-bit latch. There are zillions of example schematics on the innergoogle. For a 12 V system, this can be done with one CMOS logic chip (actually, any one of several different types), or two transistors plus some resistors. Personally, I'd go with...
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