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  1. C

    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
  3. C

    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 &...
  4. C

    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...
  5. C

    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'.
  6. C

    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...
  7. C

    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)...
  8. C

    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...
  9. C

    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.
  11. C

    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.
  12. C

    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...
  13. C

    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...
  16. C

    Bright/dim power LED mod ?

    Their blanket figures don't agree with the Bulgin datasheets I have. They give around 2V for red and amber, around 3.3V for green, blue, white. Check the datasheet for your switch & colour.
  17. C

    Bright/dim power LED mod ?

    I didn't mean "short out" as in "melt the motherboard", but it will parallel the standard switching system (ie, short it out) with the "always on" link to ground.
  18. C

    Bright/dim power LED mod ?

    I think you'll find the motherboard LED header consists of a current-limited 5V supply (where you show '+') and a switched ground (your other) so the circuit will short out the motherboard's power switching system. You could use an opto-isolator, but what's the point? The original steering...
  19. C

    HDD Activity Mod

    The circuit you show won't work, the HDDA LED header on the motherboard has 2 pins, one connected to +5V through a LED resistor, the other goes 'low' on drive activity, so your rectifier diode will block things. The basic circuit is best done with an optoisolator diode connected in place of...
  20. C

    voltage regulator needed

    If you use single LEDs and a resistor to each you don't need to worry about the state of the battery. Do the maths. A worst case 3.5V LED with 270R resistor gets 18.5mA on a full 9V cell, 9.25mA if the same battery's flattened to 6V. The difference in perceived brightness is negligible.
  21. C

    Best choice to power leds?

    If you use a power block-style adaptor rather than the wall-wart style, wiring both pump and adaptor to a junction box and single mains lead to the wall would solve the problem.
  22. C

    how to draw up a diagram?

    Circuitmaker Student was a freeware 'light' version of the very expensive Circuitmaker 2000; the producer (Microde) is no more but you'll find copies on several college sites. This one has a bit of a tutorial or the full manual is linked here. I find it very easy to use, and the schematics...
  23. C

    Can I plug a 4 pin fan into a 3 pin header? (PWM)

    It's covered in the spec linked above; PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz Maximum voltage for logic low: VIL = 0.8 V Absolute maximum current sourced: Imax = 5 mA (short circuit current) Absolute maximum voltage level: VMax = 5.25 V (open...
  24. C

    DIY anti-static wristband?

    For instance, after accidentally touching something at mains voltage; the last thing you want to be is well-earthed. :eek:
  25. C

    How do I check the voltage on a LED with my multimeter?

    Interesting...whilst it could be one of them, they're $2.55 each at Digikey, and apparently have a built-in boost converter to be able to run off 1.5-2V
  26. C

    How do I check the voltage on a LED with my multimeter?

    It's still highly unusual for a blue to register so low; the chemistry is such that blue and white LEDs are 3-4V forward voltage. I'd sooner believe an error in testing than a 2.2V blue. Testing an LED on a multimeter's "Diode Test" setting will give such a false result, they need a few mA...
  27. C

    2-pin motherboard female connectors

    It's not the contact resistance, it's the contact materials. Thermocouple connectors are in metal alloys to suit the type of thermocouple being used, so other junctions don't generate a voltage due to their local temperature and give an error. But if these connectors are mounted on the circuit...
  28. C

    IDE rounding question

    That's why the ground wires still work in a properly constructed round cable. I vaguely remember some of the early rounded cables were more gimmick than technically-sound, but I've never had data transfer problems with mine.
  29. C

    turbo led

    A lot of new (and not-so-new) motherboards have a little piezo speaker built in to the board, and the only sounds you'll hear from it will be error beeps during POST. And even those often come through your "proper" speakers instead. With a thermistor/comparator circuit you could use the LED...
  30. C

    Looking for a part

    Micrel's MIC502 sounds to be what you want, though you need to add a cap to set the PWM frequency and top & tail resistors on the pot IIRC to set the full PWM range. It's an 8-pin chip designed for fan control. There are some similar chips by Microchip, but 5V only; "A thermistor (or other...
  31. C

    AC adapter for wireless router?

    With that contradiction you really need a look inside, but I'd believe the box label. A good many routers have accurate voltage regulation to 5V (and sometimes also to 3.3V) on the circuit board and run off an unregulated higher voltage adaptor; ie, the 9V shown.
  32. C

    IDE rounding question

    Commercial rounded cables = Good Homemade for ATA33 devices (40-wire) = Usually Good Homemade for ATA66+ devices (80 wire) = Dodgy.
  33. C

    Do FM/AM/TV antennas have amps/voltage...?

    Yes, that's how the installer knows where to point them, he has a portable signal strength meter.
  34. C

    Resistors for LED

    Are you just replacing the case power LED with the LED in the Bulgin switch, using the motherboard power LED header? That doesn't need any extra resistor, there's already one fitted to every motherboard to suit the usual amber or green LED on most cases. Amber/green are 2V LEDs, so a 3V-3.4V...
  35. C

    Resistors for LED

    It's far, far more likely to be 5V, and with a blue (or white) LED any resistor between 82 ohms and 470 ohms will do. The difference in brightness is negligible - it's an indicator, not a searchlight. 180 ohms looks nice.
  36. C


    If you like shiny go for it. It's quite incredibly shiny. The only other extras over the 182B are the black interior and the snakey light, and that's a bit dodgy as the PSU needs to be active while you mess inside. I've a 182B and a torch. ;)
  37. C

    Importance of wattage for your soldering iron

    The hot flux cleans the oxide layer from the metal, so the solder wets it better. Better wetting = low surface tension = more spread. We're assuming here the iron bit is properly tinned first; with SMD parts there's enough tin already on the PCB and on the part for the tiny amount of solder on...
  38. C

    Importance of wattage for your soldering iron

    double post
  39. C

    24V from a PSU?

    Putting two molex 0V & 12V pairs in series in an attempt to get 24V is guaranteed to cause a bang. :eek: What current do you need? As said, the -12V rail is a low rating, read the PSU label for your figure.
  40. C

    Running a 12V inverter on 9V

    The wire will glow weaker on 9V. I've run 12V EL units on a PP3 battery, works OK in a darkish room. For what they cost, just buy a 9V EL. Cheaper than trying to build a DC-DC converter.