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  1. AnalogKid

    LM393 Comparator

    The 393 has an open collector output, not a totem pole output. It can pull a load down (sink current), but not up (source current). If you look at the application circuits in the datasheet, you'll see that most of them have a pull up resistor from the output to Vcc. This resistor is path for...
  2. AnalogKid

    D-Sub crimps

    It's probably easier to find a cheap serial cable, cut off one end to whatever length you need, and cut the connector out of the molding. One knife, no soldering or crimping. ak
  3. AnalogKid

    MC6802 IRQ Pulse

    It depends on what the uC is doing. One possibility is that the WDT causes a full reset every 80 ms. I agree it seems awfully short, but can't say without knowing what the application is. Another option is that the WDT ISR is very short - all it does is reset an internal counter. Then...
  4. AnalogKid

    Simulate a variable capacitor

    OR, use an analog circuit to grow a single-stage voltage-variable filter and control it with a simple pot. Was that the intent of the original question, or did I mis-interpret it? What kind of filter do you want? High-pass, low-pass, bandpass? ak
  5. AnalogKid

    MC6802 IRQ Pulse

    This is called a watchdog timer. If the application firmware gets locked up in a loop somewhere, yanking the processor into an interrupt service routine gives it a chance to examine itself to see if that is happening and take steps to correct the situation. Many newer microcontrollers have...
  6. AnalogKid

    How do get Arduino to read the angular speed of a rotating shaft?

    I don't know what kind of pre-written functions are available for the Arduino, but the basics are pretty much the same. A sensor on or near the rotating shaft sends pulse to an arduino input. Assuming once per revolution, start an internal timer when an edge arrives, stop it when the next edge...
  7. AnalogKid

    Metronome Project

    I don't understand what you mean by gcse. ak
  8. AnalogKid

    Has utility power been restored?

    If there is an AC outlet or other direct access to the incoming AC power line before the transfer switch, a fairly simple circuit could sit on the line, arm itself when power goes out, and beep when it comes back - ***without*** a power source to run the circuit throughout the power outage. If...
  9. AnalogKid

    push button circuit for quiz

    There are many quiz show circuits on the innergoogle, some dating back to the 50's. While it can be done with a bank of 555's, there are many better ways. You instructions sound like they were copied from a project on a website. Can you post a link to the original information, or at least the...
  10. AnalogKid

    Digital voltmeter - 500m cable

    A tradeoff is that the higher the meter impedance, the more susceptible it is to noise. If you don't need fast meter updates, add a noise filter capacitor across the meter input. The inductance of the cable will act as one half of a lowpass filter. ak
  11. AnalogKid

    Activate transistor with piezo disc

    do you have a schematic schematic? ak
  12. AnalogKid

    Phone with two ear phone sockets

    TRRS - tip, ring, ring, sleeve TRS - tip, ring, sleeve Many non-apple devices with TRRS connectors can detect a TRS stereo headset and adjust internally for it. So the only thing needed is a TRS simple splitter cable, 1 or 2 dollars US or equiv. ak
  13. AnalogKid

    Has utility power been restored?

    Or enable itself when power is lost, and go off when it returns. ak
  14. AnalogKid

    Has utility power been restored?

    Many photodiodes and phototransistors come with molded on lenses to narrow their detection angle. One of these pointed a one of the LEDs should be reasonably immune to false alarms, particularly if you differentiate (edge detect) the output. ak
  15. AnalogKid

    Smoke detector in sealed attic

    A high quality smoke detector is not fooled by dust; it detects ionized particles that are a byproduct of combustion. Should be ok. ak
  16. AnalogKid

    Anyone try to make a new auto battery charger "old school" ?

    Note that a 12 V batter charger does *not* mean that its output is 12 V. It means that the output is whatever the designer decided was necessary to charge a 12 V battery that actually is a 14 V battery. Peak voltage after the bridge could be 20V or more. "This must be increasing battery sales...
  17. AnalogKid

    TV commercial automatic muting device design ideas

    This idea dates back to the 50's in hobby magazines, and devices such as mm have been available since the 70's. Generally speaking, they didn't work well then, and they work less well now. In the 70's advertisers toyed with putting a code in the vertical interval (part of the non-visible...
  18. AnalogKid

    led driver selection for project

    Your question is not clear. Are you copying the Luxello product, or buying and using it? If you are buying the product, then follow the recommended power instructions. Many LEDs can handle over 300 mA, and CREE is a leader in high power LEDs for outdoor use. My guess is that there is a...
  19. AnalogKid

    Op Amp not working properly LM324

    You can eliminate the dependence on the Arduino's +5V supply by changing R2 to 26.1K. Also, note the addition of C2. This is critical to how the circuit amplifies the AC audio but not the DC offset. ak
  20. AnalogKid

    LP2950 Indecision - How would you do it?

    The output cap is there to improve system transient response. As such, its return current should *not* be involved with the feedback voltage divider. The 10 uF in the middle of the divider is there to keep impressed output noise out of the control loop. Picture B. The 10 uF cap across the 47...
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