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  1. BobK

    how to hardwire a house radio in a car - crazy project

    Why would you buy a car radio modified for house wiring when there are already many choices of car radios intended to be installed in a car? I hope you got it for a good price. That said, It most likely has an adapter for use with line voltage. You could simply leave that out and wire the...
  2. BobK

    Mixing Woodworking and Electronics

    You probably don't need the hot air right away, so, look for a pencil with a true temp control. The Weller that you pointed to was the one I previously had. It has a power adjustment, but no temp control, and I would not go back to that type of iron. Here is an inexpensive one, for example...
  3. BobK

    Mixing Woodworking and Electronics

    I used to use the inexpensive Weller station with uncontrolled temp. Then I moved up to this, when I needed a hot air station: http://www.ebay.com/itm/Kendal-2-In-1-Smart-Hot-Air-Rework-Soldering-Iron-Station-898D-/141013241092?hash=item20d50b4d04:g:DEcAAOxy79JSYVTM The difference it...
  4. BobK

    Woo-Woo The Don Smith Generator

    Eliminate the rectifiers and capacitors, and place a transformer on the output. In fact, you might as well eliminate the second transformer, then the neon light transformer, then the variac, and you will have 110VAC power. Bob
  5. BobK

    Help with "switch box" halloween prop (2leds + solenoid)

    You want the second LED and the solenoid in parallel, not in series. Bob
  6. BobK

    Woo-Woo The Don Smith Generator

    All over-unity devices are a scam. They cannot and do not work. Edited to add: The only people who get anything out of free-energy devices are those who sell plans for them. Bob
  7. BobK

    DIY led driver help

    Okay, I think I see the problem. If you just replace the trimmer with your external potentiometer, you could blow out your LEDs by turning the current up too high. So, you need a resistor in series with the potentiometer in order to limit the current to the max the LED can handle. So this is...
  8. BobK

    DIY led driver help

    You use wires to connect the three connections of the POT to the three connections the trimmer was connected to on the board. Bob
  9. BobK

    Accuracy and procedure for home-made PCBs

    Yes, I think they are OK to use. I have never used 2 transparencies and have never had a problem. You might want to up the density on your laser printer, but that might cause traces to swell a bit. Bob
  10. BobK

    Accuracy and procedure for home-made PCBs

    As long as there are no breaks and traces have adequate separation, the PCB will be functional. I would also check the scaling to make sure your .1 inch pin spacing is correct. Bob
  11. BobK

    How to convert frequency to light

    Except in deep space, the strength of a radio signal is not simply related to the distance from the transmitter. What is it you are trying to do? Bob
  12. BobK

    Electronic help

    All of the useful circuits have already been designed :) That said, the way you learn to design circuits is by studying existing designs. Once you understand how they work, try modifying them to do something slightly different. Once you can do that, circuit design is a matter of combining...
  13. BobK

    DIY led driver help

    To use that boost converter as a constant current source, you would set the voltage to a few volts more than needed (based on the LED forward voltages), and set the current limit to the current desired. You can remove the current limit trimmer from the board, as you suggested, and use a panel...
  14. BobK

    Electromagnetic Quiz Confusion.

    So what happens if you put the cell phone in the microwave? Bob
  15. BobK

    SOT-23 NMOS transistor power dissipation question

    You can get MOSFETs in SOT-23 that have much lower on resistance than the 2N7002. Less than 100mΩ is easy to find. At 200 mA, this equates to 4 milliwatts. Here is an example...
  16. BobK

    Wiring pot as voltage divider across polarities

    What you describe is two buttons, which of which will normally output 5V and can be pulled to ground when the button is pushed. The other would normally output ground, and would be pulled to 5V when pushed. These are suitable to connect to an input that does not draw much current. Is that...
  17. BobK

    Wiring pot as voltage divider across polarities

    A voltage control circuit does not "output a current". How are you measuring this? Are you putting an ammeter between the signal and ground? If so, do not do this, you are likely to destroy something. An ammeter is essentially a short circuit. The input using the control circuit will draw...
  18. BobK

    How can I remove the underling waveform from a signal

    And on my recent DSO, you use the math function and subtract, which displays the difference between the two signals. Bob
  19. BobK

    Interfacing with a PIC Microcontroller

    1. I use all of the PICs except the 32-bit ones, so I can't help you with choosing a chip. In general though, choose one that has enough I/O pins and internal devices (like ADCs) that you need. 2. The manufacturer does not send you a programmer with the chip. You buy it separate from the...
  20. BobK

    Can 7.4V 1900maH battery positive lead fry Raspberry Pi if attached to ground GPIO pin?

    You have not told us enough about this to answer your question. What is the - terminal of the battery connected to? If you simply connected the + lead of the battery to the ground of the Rpi, then nothing would happen. If the - lead of the battery was connected to the same ground, your...
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