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  1. AnalogKid

    Simple Hall sensor alarm circuit?

    The two transistors are connected as a Darlington pair for increased gain. ak
  2. AnalogKid

    Simple Hall sensor alarm circuit?

    Without a datasheet or pinout for the BC547, or a schematic, it's hard to say. I can note that it *appears* that you are applying 9 V to a 5 V buzzer. Also, 100K is a very large value for such a high gain circuit, and enables false tripping due to noise. Reduce to 10K. Also, when the door is...
  3. AnalogKid

    Simple Hall sensor alarm circuit?

    Or a different Hall sensor. IIRC, don't the same people make one that has an open output in the presence of a field? Not at my computer; can't search. ak
  4. AnalogKid

    Simple Hall sensor alarm circuit?

    Yes, you probably have damaged the sensor. With pin 3 connected directly to 9 V, when the sensor is tripped it attempts to put a dead short across the battery. This probably has blown its output transistor. To correct this, break the connection between pins 1 and 3, and connect the buzzer...
  5. AnalogKid

    24v to 12v converter

    Agree. There are a lot of fins, but not enough for a linear regulator. But wait - that statement assumes western science design values. If we assume a cheaper-than-dirt ethic, it *is* a linear regulator, and assumes direct exposure to a 40 mph air stream. ak
  6. AnalogKid

    Latching switch

    Actually, if the switch is self-latching (called an alternate-action switch), you don't need a circuit. If the switch is a simple momentary pushbutton, then a circuit can transform this into alternate-action performance. Which is it? ak
  7. AnalogKid

    Circuit not working like intended...help please!

    What is the piezo beeper you are using? Part number / web page / datasheet? Specifically, does it beep continuously when powered by DC, or does it require an oscillating signal? Is the 555 supposed to be a monostable timer, making the piezo beep for a short period of time, or is it an astable...
  8. AnalogKid

    constant current source with transistor

    I'm trying to follow along, but it is difficult. Please post a schematic of the oscillator. Be sure to use the correct symbol for each component, and include a reference designator and part value. ak
  9. AnalogKid

    How to reduce IR sensitivity for can trash

    What is the question?
  10. AnalogKid

    Help wiring vintage record player speaker

    It is high voltage DC with AC ripple superimposed on top of it. The DC value depends on the AC mains voltage and the rectifier configuration. The AC ripple is what causes the background hum out of the speaker. There are several rectifier/filter capacitor configurations. We can't get into...
  11. AnalogKid

    Help wiring vintage record player speaker

    Your image has the speaker magnet assembly (large steel rectangular shape lower left), the amplifier output transformer (transformer-looking thing upper left) and a connector (round thing upper right). The yellow and yellow-stripe wires from the connector go directly to the magnet. Those are...
  12. AnalogKid

    Veeder Root 6 Digit electric counter . Does it work ?

    The front panel does not look right for an elapsed-time indicator, so it probably is an impulse counter. A small 115Vac solenoid ratchets the wheel mechanism. Sometimes these units do not like continuous activation, so drive with a pulsed signal. You do not need any external current limiting. ak
  13. AnalogKid

    Silent Switch for MIDI Surface Controller

    Conductive rubber key switches are very quiet, with a slightly tactile but almost completely inaudible little thump. The tradeoff is that the contact resistance can be tens of ohms. ak
  14. AnalogKid

    Silent Switch for MIDI Surface Controller

    Photos of the current device so we can see what kind of space we have to work with? PCB or wired switches? ak
  15. AnalogKid

    Circuit works with any LED, s long as one is red.

    Here is a link to what probably is the origin for this circuit. http://www.cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html You might be right on the hairy edge of your particular transistor's avalanche voltage. Power the circuit with two 9 V batteries in series and...
  16. AnalogKid

    110 220V detection

    Again, #2 and #5. ak
  17. AnalogKid

    110 220V detection

    Sounds familiar ... wait ... Aha - post #5. ak
  18. AnalogKid

    Front panel fabrication - low cost shops

    Back when I was actually paid to sit on my butt in front of a computer for much of the day, I had a 40,000 sqft metal shop underneath my office. They were magicians, and I am permanently spoiled. I can do good enough panel work, but it is tedious. There have been several threads about low...
  19. AnalogKid

    I Need a Device that Can Tell a PC the State of Relay Contacts

    Since you brought the good old parallel port days . . ...
  20. AnalogKid

    110 220V detection

    Following up on crutschow's solution, there are two different configurations for a single-relay solution. Start with one 240Vac relay with DPDT contacts. 1. The relay completely connects/disconnects two separate banks of heaters, one for 240 V and one for 120 V. To save a nickel, this can be...
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