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Recent content by cpemma

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    how can I make my own fanamp?

    That's not straightforward, the mobo signal isn't a nice DC level, it's very load-dependent so geared to a "typical" fan power. Increase the load and the voltage will drop. Using a single "typical" fan plugged into the mobo and following its voltage to pass to the other fans seems one way.
  2. C

    Hard Drive LED Voltage

    Further to other answers, the HDDA LED is running from a 5V source via a suitable resistor built into the motherboard (and a transistor switch in the HDD). So a straight swap to any colour is possible. Same goes for the case power LED
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    Computer fans that can spin the other way and how to do that?

    Correct. A brushless fan has electronic commutation, the electronics would be damaged by a reversed power connection (so there's usually a diode in the circuit as a safeguard). The only way to reverse the spin is to remove the permanent magnet ring inside the rotor, flip it over to swap the N &...
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    How to make a Multi Channel Bay Bus? I don't like any of the prefab crap

    Erm, not quite, the 317 tab is connected to the output voltage so if it (or its sink) touches grounded metal you get the POOF! To my mind a fan regulator should cover around a 5V-up range, anything lower may not be enough to start the fan. Solution with the LM317 is a fixed resistor in series...
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    Checking my math on rheostat requirements

    You can make a decent high-current voltage-follower circuit with an op-amp and a PNP power transistor, so maybe one IC is an LM324 quad op-amp. The other possibly the same IC controlling the LED brightness. Whoops. Didn't think that was a transparent gif. Right-click, 'View image'.
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    Checking my math on rheostat requirements

    From the size of the heatsinks I reckon that's a linear regulator; they would be total overkill for a PWM circuit. Some figures here. Running regulators in parallel to get more current is dangerous, it's safer if you have 4 dropper resistors (1 on each channel) rather than the single one. Much...
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    Temperature controlled switch? Thermostat?

    Add a feedback resistor R7 as in the Velleman circuit. A lower value gives more hysteresis. They've only used 2 bits of the quad LM324 and one of those is just a voltage follower helping regulate the 5.1V reference voltage. With a well-regulated PC 12V supply, a single op-amp (or comparator)...
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    Temperature controlled switch? Thermostat?

    The wall-mount one controlling my CH radiators is the simple dial and bi-metallic strip type and has mechanical change-over contacts (no relay involved) to suit the different types of motor-actuated valves on the market. A bit bulky but it would do the job. The fancy ones that show the...
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    Temperature controlled switch? Thermostat?

    You'll need a thermostat with normally-open or change-over switch contacts, as the usual action is for them to turn something on when it gets colder than the setting. Failing the domestic thermostat, Velleman do a kit and ready-made-up unit that will run off 12V and switch up to 3A.
  10. C

    How to make a monetary switch into on off?

    4 different ways. The 555 circuit is simple if starting in the 'Off' state suits.
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    PSU capacitor solder question!

    With the PSU off & unplugged you can check the if the tracks you've soldered the negative cap leads to are grounds with the multimeter on 'resistance' and a known ground (any black molex wire) for the other test point. Meter should read zero.
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    How to wire a pulsing light (halloween)

    True, the best way is to make sure the "full" setting is still a low forward current as the difference in perceived brightness from about 5mA to 20/25mA is negligible (the eye's sensitivity to light is near logarithmic, we've evolved to see danger in the shadows ;)). A 2-op-amp triangle-wave...
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    HDD Activity Mod

    There is, it's already fitted on all motherboards to suit the case LED normally attached to that header and also suits an optoisolator LED. ;)
  14. C

    I need a cheap benchtop power supply

    For cheap you could base on a 24V SMPS brick adaptor, here's one that will deliver 2.5A with short circuit and over voltage protection built-in, and more powerful models are available if you feel 4A is needed. For variable output add an LM338 5A regulator on the back end but remember at high...
  15. C

    Bright/dim power LED mod ?

    What happens is, the motherboard puts 5V across its own resistor plus the LED, the red LED takes 1.85V (its forward drop) and the motherboard resistor the rest (3.15V). On my mobo it's a 240-ohm resistor, so with 3.15V across it, it allows 13mA through the LED, plenty adequate for an indicator...
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