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  1. K

    Will this work?

    A SPST switch with an LED typically has 3 terminals: in, out, and ground, and the LED (with a built-in resistor) is connected between out and ground. If you wire the two switch terminals incorrectly, supplying 12V to the output terminal instead of the input, the LED will stay on all the time...
  2. K

    Passphrase & Password - is there a difference

    The router likely has two passwords/phrases: one for the WiFi security (WPA2 hopefully as it's the most secure) and is needed for devices such as your tablet to connect to the network. The other is likely to gain access to the administration pages on the router (to change settings, etc.)...
  3. K

    'Soldering press'?

    Sounds like you need a hot air rework station. They make it a lot easier (and faster) to solder, and more importantly, unsolder SMT parts when doing repairs.
  4. K

    Advice for 12v dc fan switch

    The optimum voltage for a 12V fan is 12V. The current draw will depend on the fan. Some draw more current than others. Usually the current at 12V is printed on the fan label. The current will be higher at startup and if the fan is loaded down (by the magnet/stirrer), so take that into...
  5. K

    Make:Electronics Page 85

    That's a PUT (programmable unijunction transistor), not a PNP. The two resistors form a voltage divider that sets the gate voltage to about 2.1V, which "programs" the transistor to fire (turn on) at a determined threshold voltage as the capacitor charges through the 470K resistor. Changing...
  6. K

    RC OSCILLATOR in pic16f877

    Actually, you should use a higher frequency crystal. 32 KHz would make for a really slow processor that couldn't handle more than a few hundred baud. Use something like a 4 MHz crystal, or an 8 MHz if you need some more speed. If you need accurate RS232 standard baud rates like 9600, 19200...
  7. K

    Small RGB led cycle

    6" x 4" x 1" thick is plenty of space for a small board and some AAA or AA batteries to power the thing. The circuit should fit a perfboard and be small enough to fit in your enclosure. There are a couple "fading LEDs" circuits here: http://www.bowdenshobbycircuits.info/fade_led.htm One uses...
  8. K

    Small RGB led cycle

    You could create three low-frequency triangle wave oscillators with a few transistors or op-amp ICs and set them to different frequencies so they ramp the colors up and down independently, but once you've done that you will have more parts on the board (and probably higher cost) than if you used...
  9. K

    Discharging a capacitor to safely work on a camera

    If you use a voltmeter, use the DC setting. Depending on the meter, it may not discharge the capacitor very quickly, but it will tell you the voltage charge remaining on it. I would also use a higher setting initially (250-300V or higher if available) and take a reading. Once it drops below...
  10. K

    Bluetooth PIC connection

    When you stop passing data to the UART (by writing to TXREG on a PIC) it will stop transmitting data (after it finishes sending the last byte/word you gave it). When you start writing data to TXREG again, the UART will start sending the data again. Do you mean you want the BT module to stop...
  11. K

    Small RGB led cycle

    The best way is with a microcontroller. They are different than microprocessors as in they're self contained, very few supporting components are needed. For a basic one all you'd need is the chip, a power source, and (ideally) a decoupling capacitor across the power leads. Maybe a pull-up...
  12. K

    Supply current in relation to the total current consumed by a circuit

    If you want to play it safe wire a 1A fuse in series with the 5V supply going to your circuit. That way, if something goes wrong (short circuit or something), the fuse blows rather than something drawing the full 5A and releasing the magic smoke from your circuit.
  13. K

    flip relay with 2n3904

    What relay is it? So I can see the data sheet. Usually if a relay says "5V", it means the coil is rated for use at 5V. It can handle more, and should work with (at least slightly) less. But if you put too much voltage (and more specifically, current) through, it could heat up and burn out.
  14. K

    Panasonic SA-200HE receiver not turning on

    Start at the power supply. See if it's putting out the correct voltages. Having a schematic is an excellent first step, sometimes they can be hard to come by for consumer electronics. :)
  15. K

    need help in counter programming+ pic16f877a

    The way I do debounce is like this (this is pseudo-code, not an actual language): begin loop if (buttonstate != lastbuttonstate) count = 100 (adjust this based on the speed of your loop) lastbuttonstate = buttonstate endif if (count > 0) decrement count if (count ==...
  16. K

    Question about voltage input before speaker

    The relay would only be powered when the alarm is sounding, so you wouldn't be using more energy (current) except when the alarm is going off and the relay is activated. Are you planning to power an AC-powered lamp? You'll need a relay for that.
  17. K

    Question about voltage input before speaker

    Sounds like your speaker is low-side switched, meaning one side is connected to the positive supply and the alarm signal (or power, if it's a buzzer and not a speaker) is controlled on the ground side through an NPN transistor or N-channel FET. You could still wire it up to turn on a light, you...
  18. K

    Puppy with light up fan

    You got more hair out, so does the fan spin now? Does it light up now?
  19. K

    Puppy with light up fan

    Does the rotation resistance change with it turned on? Check the batteries anyway, if they're weak they could still have enough to power the music chip but not enough to spin the motor. If you can pull the fan blade off the shaft, there may still be hair clogging the motor bearing. Depending...
  20. K

    Level Shifting

    Bipolar transistors are controlled by current, not voltage. In a typical circuit as you describe, you'd have a base resistor to limit base current to a few mA (depending on the circuit, your circuit's needs, and the gain of the transistor). With the resistor in place, you could feed 9V into...
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