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  1. Alec_t

    Replacing a 9Vdc relay with a transistor switch

    Perhaps use an opto-triac (e.g. a MOC3023) driving a triac to switch the thermostat contacts? Just a few mA would be needed for the opto input. An equivalent of this assembly is available off-the-shelf as a SSR (solid state relay).
  2. Alec_t

    How to best simply invert a 110v ac current w/minimum change to the voltage

    Since the signal has to pass through some device to do the inversion, and since no device is perfect, there will inevitably be some distortion.
  3. Alec_t

    How to best simply invert a 110v ac current w/minimum change to the voltage

    If you're looking for phase inversion, just use a 1:1 ratio transformer.of appropriate rating.
  4. Alec_t

    Max temp for caps

    Beware the Dark Side!
  5. Alec_t

    Replacing a 9Vdc relay with a transistor switch

    More details (especially a schematic) of the sensor would help. Is one of its two terminals being shorted tied to either power supply rail, for example?
  6. Alec_t

    cheap mains stepdown 240-120

    Sadly, no. That will drop the output volts too much, because the added primary isn't magnetically coupled to the existing primary. What you need (according to the Spice simulation attached) is an inductor (or transformer primary) with an inductance about 40% of the existing 120V transformer...
  7. Alec_t

    Car power inverter limits

    What are the power requirements of the Playstation and screen? The output of the inverter is described as 'modified sine wave'. Not all loads are happy with that.
  8. Alec_t

    A Quick LED Question...

    Oops! My bad. In post #2, 467 and 470 should read 46.7 and 47 respectively. Spot on!
  9. Alec_t

    Piezo-triggered twinkling LEDs

    In view of the limited space available, a microprocessor to do the timing and randomising would be the obvious thing to use. Tiny, yet versatile, micros are available (e.g. a PIC).
  10. Alec_t

    A Quick LED Question...

    Welcome to EP! The LED in the link has a typical (it always varies from one example to another) forward voltage (Vf) of 2.3V and a current rating of 20mA. Because of Vf variations it is not good to wire LEDs directly in parallel (one will tend to hog the current and so be brighter or have a...
  11. Alec_t

    need a switch that will deactivate with man overboard

    The reed-switch would also do the job. Forget the bit of metal. Just tie the magnet to a pull cord. Magnet next to reed, switch contacts close. Magnet pulled away, contacts open.
  12. Alec_t

    frequency range too small on 555 timer circuit?

    Here's how you could get the frequency and duty cycle you want, using half of a six-inverter IC such as the 74HC04. Frequency (0.2Hz to 2Hz) and duty cycle (2% to 98%) are independently adjustable.
  13. Alec_t

    Carbon Monoxide detector circuit

    Not for long with continuous use. According to the datasheet the sensor average power consumption is ~350mW at 5V, so would be ~ 126mW at 3V. If D cell capacity is 20Wh, 2 D cells should run the sensor for ~ 2 x 20 / 0.126 = 317 hours (< 14 days).
  14. Alec_t

    AC Compressor blowing fuse

    Definitely sounds like an intermittent short in the wiring from the fuse to either the clutch or to some other load.
  15. Alec_t

    More efficient LDR "dark" switch?

    Don't give up yet on the analogue approach ;). I think the reason you weren't getting much LED current was because you didn't do the Darlington mod Colin suggested in post #8 ? Without the mod the transistors drop ~ 0.7V. With the mod they drop only ~0.1V. Here's a sim showing the current boost...
  16. Alec_t

    Anyone made a sound card oscilloscope?

    As an alternative to using a VCO, you could try using the DC level to create a PWM signal. Might be simpler/cheaper, depending on how linear/accurate the result needs to be.
  17. Alec_t

    Martin MP-2000 Fog Machine problem

    Sounds like the BTB24 (triac) is being asked to pass excessive current. Have you checked that the heater isn't short-circuited? Can you check its resistance against that of a known good heater?
  18. Alec_t

    Can I use a blender motor as a fan?

    Methinks you'll find the motor noise very annoying :(. Fan motors are normally an induction type (much quieter than a universal motor)
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