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  1. AnalogKid

    Portable USB phone Charger Design Help

    There is nothing magical about the Minty circuit, meaning nothing that makes it compatible or incompatible by design with various devices. It is a generic boost circuit making a generic USB power output. If your phone won't work with it, it almost certainly will not work with anything else you...
  2. AnalogKid

    Psychic amplification apparatus - calculating inductance??

    I see a 6.8 V zener diode. ak
  3. AnalogKid

    Audio Through Relays

    The MAX4359 is a fully integrated 4x4 routing switcher, but it is designed for video and might not have the noise/distortion performance you need. Still, I'd look into it because it might save a ton of work. ak
  4. AnalogKid

    Audio Through Relays

    What comes out of a guitar pickup is about as AC as AC can get. And if it is kept as a balanced signal, then you do indeed have to switch both lines. But if you ground one end (as many amps do), then it is one unbalanced signal line and a ground. Straight out of the guitar, the voltage...
  5. AnalogKid

    555 Timer Push-On, Push-Off but with timer as well

    The circuit in post #3 is a bistable, or toggle flipflop that latches alternatively in the high and low output states. It does not have the one minute timer in post #1. To modify your original circuit, change the pushbutton switch to a SPDT toggle switch that is center-off and momentary in...
  6. AnalogKid

    Audio Through Relays

    Since the entire rig is mono and unbalanced, everywhere you show two switches there actually is only one. You do not want to switch the grounds if you can avoid it. If you have relays or solid state switches, they must be powered and controlled. For all analog switches, how were you going to...
  7. AnalogKid

    Rotary sensor with logic output, kind of...

    There are only about a dozen ways to detect that an axle or shaft is rotating, and without knowing more about your physical arrangement, all recommendations are merely guesses. For example, is gluing or taping a magnet to the shaft ok, or would that throw something out of balance? Must the...
  8. AnalogKid

    Audio Through Relays

    For a fully reconfigurable system with three pedals you'll need 15 relays or analog switches, 16 if you want a full bypass mode. ak
  9. AnalogKid

    Audio Through Relays

    If you have multiple sources and multiple destinations, what you are describing is a routing switcher. Are all audio signals at guitar pickup voltage levels? How many audio signals are there? Are any stereo, or all mono? Balanced or unbalanced? What do you mean by "switch the order around"? Can...
  10. AnalogKid

    Help rebuilding High School project

    Looks good so far. What ever decoding or diode-ORing you do, you have to account for the counter 0000 state Your table has 7 states and a die has 6. As it is now, your circuit might stop on 0000 and make no display. ak
  11. AnalogKid

    Help rebuilding High School project

    It's not a random pattern, just a pseudo-random system because the clock is so fast relative to the time it takes for a human to press and release a button. There are 6 4017 outputs and 7 LEDs. Thee only real problem with this approach is the low output current of the 4017. At 20 mA per LED...
  12. AnalogKid

    Help rebuilding High School project

    The circuit in post #2 can be the starting point for a dice display. That circuit runs at a constant speed until the switch is released, then stops dead. Another variation is a "Wheel of Fortune" circuit that emulates a rotary game wheel in that it starts out fast, then slows down to a halt...
  13. AnalogKid

    Door Alarm Help Please

    Here is a version of the door alarm circuit using conventional logic gates. Note that there are three separate output stage options. U1D can sink over 20 mA, but is limited to 5 V beeper voltage. Because of its relatively high Rdson, Q1 is for low power beepers, but can handle higher output...
  14. AnalogKid

    How to keep 7805 from overheating?

    The power dissipated in a series voltage regulator such as the 7805 equals the differential voltage across the device times the current through it (plus a small amount of power used by the regulator itself). With 12 V in and 5 V out, the differential voltage is 7 V. At 40 mA out, that's a peak...
  15. AnalogKid

    Another transistor discussion

    First, I'm not picking a fight. I've read your stuff, and you know your stuff. But... For common emitter circuits, maybe, but not for emitter followers. In the output stage of a power supply or audio power amp, base current flows directly into the load, and can account for 5% to 10% of the...
  16. AnalogKid

    Another transistor discussion

    I completely and totally agree. And, it always surprises me how difficult this is to teach (or hammer into, depending...) young'ns. ak
  17. AnalogKid

    Door Alarm Help Please

    The request was for something to latch the beeper *off*. The FF does that. Only the door can turn on the beeper. There is no on-state latch, only off-state. SW2 latches off the beeper. My guess is for those times when the door is open intentionally, such as ventilation in the summer. Closing...
  18. AnalogKid

    Door Alarm Help Please

    Here is a first pass at a door alarm circuit. Each section of a ULN2004 is a darlington transistor with 1/2 amp collector current capability, base current limit and pull down resistors, input and output transient protection, and can run on anything from 5 to 18 Vdc. U1E and F form a flipflop...
  19. AnalogKid

    Door Alarm Help Please

    So a ff to disable the alarm sometimes, and the same action that normally disables the alarm clears the ff. This will fit in one ULN2003 (plus 5 resistors) with each stage acting as an open collector inverter. The whole circuit can run on anything from 5 to 48 Vdc, has input and output...
  20. AnalogKid

    NO CONTACT CURRENT AND NC CONTACT CURRENT OF RELAY

    Yes. One of the things that determines contact rating is the force or pressure applied, pressing the contacts together. The higher the force, the higher the contact rating. For the NC contact, the contact pressure is provided by the return spring only. This sprint strength is a compromise...
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