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  1. crutschow

    How to safely short the leads of a DC motor together with no power is applied.

    That's an 85A rated unit. I thought you wanted 100A? As Minder's schematic shows, it is a DPST (alternate poles on). It has 6 terminals but not 6 poles (as defined by relay convention "The pole of a relay is the terminal common to every path. Each position where the pole can connect is called...
  2. crutschow

    How to safely short the leads of a DC motor together with no power is applied.

    The COM terminal goes to the motor, the N.O. terminal goes to the power supply, and the N.C. terminal goes to ground/common. The motor then receives the supply voltage when the relay coil as powered, and is grounded when the relay coil is not powered.
  3. crutschow

    How to safely short the leads of a DC motor together with no power is applied.

    Perhaps one of these 100A SPDT relays would work. Edit: Here's a solenoid type that looks more robust.
  4. crutschow

    Simple 555 Timer

    Why is that a problem? Is the power not applied continuously to the circuit? Try connecting the positive side of C2 to the V+ supply, and the negative side to pin 6 and R3. Also change R1 back to 10kΩ. R3 is not needed--you can connect pins 6 and 7 together. With that the 555 should power up...
  5. crutschow

    Simple 555 Timer

    What is a "staircase timer"? What is the purpose of the 555? What exactly do you want the circuit to do?
  6. crutschow

    Reverse Photoresistor for volume control when nearing

    For that you need a distance sensor, not a light sensor.
  7. crutschow

    hacking a smoke alarm

    Don't see that it's significantly more complicated than using an RF sniffer or hacking into the alarm.
  8. crutschow

    Off the Shelf Logic Gates?

    And here come your usual assortment of non-sequiturs.
  9. crutschow

    hacking a smoke alarm

    You said smoke detectors, so one way would be to add a microphone and amplifier to detect the alarm sound from the detectors. A simple analog band-pass filter would likely need to be added to suppress other than the alarm frequency (typically between 2kHz to 3.5kHz). Also have a delay in the...
  10. crutschow

    Off the Shelf Logic Gates?

    I would say 5 years is more than "a little late". :rolleyes:
  11. crutschow

    Trigger 12v relay with 3v source

    Here's the LTspice simulation of a circuit similar to what Bluejets suggested: It uses a Darlington output opto coupler (for isolation if the LED is low-side driven) with a high transfer gain, driving a MOSFET driver for the relay to minimize the current drain from the tach LED: It works because...
  12. crutschow

    Fuel level switch

    Then it's terrifying to imagine your psychedelic mind when it's not sober. :eek: Not surprising. I tend to make comments about other posters weird comments.
  13. crutschow

    Trigger 12v relay with 3v source

    Do you have access to what is driving the LED or just the LED leads? What powers the LED circuit?
  14. crutschow

    Fuel level switch

    You really need to sober up so we can understand what you are saying. :rolleyes:
  15. crutschow

    LM394 National Semiconductor 'supermatch' NPN pair

    Do you know how to connect to such a small, surface-mount device?
  16. crutschow

    LM394 National Semiconductor 'supermatch' NPN pair

    There are dual transistors available in a single package that should work better than two discrete transistors.
  17. crutschow

    Fuel level switch

    Or wait for the TS.
  18. crutschow

    Fuel level switch

    Well, you are reading way more into than I am.;)
  19. crutschow

    Fuel level switch

    A window comparator using comparators with open collector outputs, such as the LM339, can have the outputs connected together with one resistor pull-up to generate an output wired-AND function, for a simple steering mechanism (example below): So, within the window, both comparator outputs are...
  20. crutschow

    Fuel level switch

    Is the resistor by itself or is it connected to a fuel-level gauge or other connections? A window comparator should also work.
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