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  1. S

    555 timer for a fan

    I switched to a supply of 5 V when I found a 5 V fan. The voltage coming out of the 555 output is 3.5 V and I figured a 300 ohm resistor would give at least 10 mA which should which at 40 hfe should give 400 mA. My fan only needs 180 mA but the voltage across the transistor is 2.7 V so the fan...
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    DMM allows current to pass but measures 0 mA

    By luck I noticed that when the multimeter is squeezed a little it behaves correctly and determined that the PCB wasn't pressing the back of the dial well enough. I opened it up and tightened a screw at the bottom while pressing on the PCB and now it works as expected. :)
  3. S

    DMM allows current to pass but measures 0 mA

    I have a UNIT UT61E DMM. I have the probes in the correct sockets and the dial set to mA. When connected to a circuit with about 13 mA passing through it (measured with a different DMM), the reading is 0.000. Perhaps in an unrelated issue, when I move the dial to A and move the probe to the...
  4. S

    555 timer for a fan

    Okay, I will use a CMOS version instead. Thanks again for your help.
  5. S

    555 timer for a fan

    https://electronics.stackexchange.com/questions/149763/wiring-555-to-disconnect-itself-from-electricity
  6. S

    555 timer for a fan

    This is the final circuit offered on Stack Exchange. Do you think it wouldn't work? I'm still trying to get my head around it. The button needs to provide power and activate the trigger at the same time.
  7. S

    555 timer for a fan

    Thanks for your help. I've moved the transistor but I also have another problem in that the talkingelectronics website says the 555 timer chip uses 10 mA while running which means it will be draining the battery during the periods where the fan is off. I'm trying to figure out a way to make the...
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    555 timer for a fan

    Thanks. I added the transistor. Do you know whether value of the non-timing capacitor on 555 chip pin 5 matters much? I've read that 10 nF is appropriate and I happen to have one that seems to be 30 nF. I figure it's not critical, so long as it's at least 10 nF but I'm not certain.
  9. S

    555 timer for a fan

    I would like to use a 555 timer to power a fan for ~4-5 minutes when a momentary switch is pressed. I read that the motor should have a flyback diode to protect the circuit - does it matter what the specification of the diode is or will anything work? I read that the 555 chip can source 200 mA...
  10. S

    Cooling soldering iron quickly after use to reduce oxidation

    In my perennial battle to stop my soldering iron tip from oxidising, after switching it off, I rub it against a block of sal ammoniac and then again on my damp sponge to cool it off. I was wondering whether anyone else is concerned about cooling their soldering iron back down after use (I was...
  11. S

    Small low-power light sensor

    Thanks very much. I ordered some 74LVC1G14. I may use a larger battery but I only expect it to be used for minutes per day so it will last long enough.
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    The dark theme isn't very dark

    I appreciate that the dark theme is darker than default but it's not as dark as a typical website dark theme. It could go much darker if the text was made lighter as well. And the text entry box is still white!
  13. S

    Sound cancellation

    This video suggests that sound cancellation is possible with just a microphone, amplifier and surface transducer but doesn't explain how the sound being produced by the speaker/transducer is ensured to be 180° out-of-phase with the sound going through the panels. Is it the spacing between the...
  14. S

    Small low-power light sensor

    I would like to make a very small battery (~100 mAh) powered light that turns on automatically when the light level is low. The device will spend most of it's time in light (i.e. stand-by) so it's important that the sensor consumes low power. The LEDs will probably be one or two red SMDs. I...
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    Comedy Thread

    This stock photo of someone soldering. That's gotta hurt!
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    Uninterruptible power supply ratings: conflict between VA and W?

    My understanding is that P = VI and therefore the power rating of a device in VA should be the same as W but this doesn't seem to be the case for every uninterruptible power supply I look at where the VA rating is much higher than the rating in watts. What's that about? Here's a random example...
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    LED in distilled water?

    To reiterate what others have said, deionised water is corrosive and therefore won't stay deionised for long; it will slowly gain ions by corroding stuff unless, perhaps, you can apply a suitable coating. Perhaps a coat of nail varnish or insulating varnish would prevent electrolysis without...
  18. S

    Could a water flow sensor sense gas flow?

    Could a water flow sensor like this one be expected to detect gas flow also? I don't need an accurate measurement; just whether or not there is gas flowing. If not, why?
  19. S

    What is the name of this kind of connector?

    I'd like to buy a three- or four-pin connector like the one in the picture below but I don't know what this kind of connector is called.
  20. S

    Is it possible to replace keyboard LEDs with neon indicators and a single inverter?

    Version 2 has triacs and opto-couplers! Edit: MOC3010 should maybe be MOC3083.
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