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  1. BobK

    Output of logic gate as ground?

    You must also look at the specs of the device to see how much current it can sink. Some are limited to a few milliamps and might not be able to drive an LED they way you are asking about,. Bob
  2. BobK

    Controlling LEDs using the serial port

    If you want to control external devices from a PC, the best method is to get a USB interfaced GPIO board like this one: http://numato.com/8-channel-usb-gpio-module This connects to you PC and lets you control 8 separate outputs or read them as inputs. Bob
  3. BobK

    DC to DC conventer

    Here is a bright idea: Lots of automotive light bulbs. 80 25W ones would do. And you could rent it out to road crews doing construction at night. Bob
  4. BobK

    Help sizing a potentiometer

    My rule is that if you need to worry about the power rating of a potentiometer, you should not be using a potentiometer that way. PWM is far superior and often cheaper than a potentiometer or rheostat with sufficient power handling capability. Bob
  5. BobK

    Please Help? Vacuum Tube TV

    Yes there is. The later model TVs with picture tubes use mostly semiconductors and even ICs for other parts, in fact they were advertised as solid state. Bob
  6. BobK

    Chinese Electronics Sales

    I have bought from DX. The merchandise is iffy and they take forever to ship. Expect about 3 weeks. Bob
  7. BobK

    Embedded music player

    There are dsPIC processors with an Audio DAC built in. This is really quite a capable processor for audio, though it got panned by people who had no clue how to use it, I can testify it does work well. The dsPIC33FJ64GP804, costing $5.00 single quantity, has a stereo 16-bit Audio DAC. The DAC...
  8. BobK

    Looking for basic circuits on RGB LEDs

    The strips with "individually addressable" LEDs are actually shift registers. You shift in 24 bits (8-8-8- RGB) for each LED in the strip. There is no simple way to do this without a microcontroller. Bob
  9. BobK

    Adding voltage to a circuit?

    Also note that if you add voltage sources in series, the current limit will be that of the lowest source. Bob
  10. BobK

    Scratches/scoring on photo etched PCB

    I am using the photo-resist method and have never seen scratches in the resist. I have used boards from MG chemicals and boards from China off Ebay with good results. My main problem tends to be copper left behind on the edges of the board or from dust during exposure. I do not touch the...
  11. BobK

    Powering LEDs from batteries

    If they did not go up in a flash, you probably connected them backwards. But don't reverse the connection without a resistor. Use a 150Ω resistor in series with each LED. Bob
  12. BobK

    Splicing right and left channel to one earbud/headphone

    You can connect both channels through resistors (1K would do) to a single input on a mono amp to get a mono out. Bob
  13. BobK

    Need Some Help Figuring Out How to Use the PDSP2112

    The pauses are specified as a minimum, they can always be higher. You will not lose much speed by just pausing 5.4uS for each operation. Once set up it could do a character every 10.8 uSec + the time to move the data, say 4 more uS, so say 14.8uS per character or 67567 characters per second...
  14. BobK

    transistor beta and saturation current for switching

    Also, Hfe only really applies in the linear region. In saturation, a rule of thumb is to us 1/10 of collector current. Bob
  15. BobK

    Problem with Power Transistor MJ10012

    Get an optically isolated triac AKA a solid state relay or SSR. They are designed to switch AC loads with an isolated low voltage DC control. Bob
  16. BobK

    Is it possible to limit current with constant voltage?

    Since no one answered the question in the title of the thread... The answer is no. You can limit either the voltage or the current but not both. For example, if you have a 5V supply and a device that needs 2A at 5V, there is no way to limit the current to 1A other than lowering the voltage. Bob
  17. BobK

    Can I use a resistor as a fuse?

    What is 1% of 0? What is 10% of 0? Tolerance for zero Ohms cannot be specified as a percentage. Bob
  18. BobK

    ASG (Airsoft) - Sound Grenade

    I saw a great circuit somewhere that charged a capacitor to about 300V (using the guts form a throw away flash camera) then discharged it into a high wattage speaker to make a realistic explosive sound (supposedly). Bob
  19. BobK

    Resonance Basics

    No, electrical systems oscillate as well. Where do think the sound comes from in Moog synthesizer, are there little glasses in there and midgets running their fingers around the rims? Look up oscillator circuit. There are many different ones. Bob
  20. BobK

    Non-changing current with C-EMF

    "Fast enough" is a useless description. Any constant current source will track changes in the load and compensate within some amount of time. This might be 1uS or it might be 1S. Either of these are "fast enough" for someone's application. What is your requirement? Bob
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