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  1. BobK

    Heating coils with a 9v, why doesn't this work?

    18650's are capable of much more current than a 9V, but are at a lower voltage. Here are some nice charts about Nichrome wire: Nichrome wire 28 gauge wire is about 4Ω per foot, and it takes almost 3A to heat to 1200 F which is what you would need to be "red hot". Less if you coil it. A...
  2. BobK

    Please help to buy those components

    These are not off-the-shelf components. Does not the book not tell you how to make them yourself? Bob
  3. BobK

    Christmas Tree LED lights

    Here is one that has an on resistance of 147mΩ at 2.5V and can carry 2A. Perfectly suitable for 3V switching. http://www.mouser.com/ds/2/308/MCH3481-D-775525.pdf Bob
  4. BobK

    Advices for building PCB prototype that plays music via bluetooth

    Try Ebay or Ali Express. There are very cheap boards available that do exactly this. You could not make one from parts for less. Bob
  5. BobK

    Heating coils with a 9v, why doesn't this work?

    Actually, you should be able to get some heat from a 9V battery for a short period of time. A fresh one should be able to supply about 1A, but only for minutes. What size of nichrome wire did you buy? You would want a fairly fine one. Bob
  6. BobK

    Christmas Tree LED lights

    Most likely, the lights are wired in series and run directly from the line voltage. Unless you have the experience, working with line voltage is dangerous. But we can probably determine that. Is there a box between the line plug and the lights? If not, then they are running at the line...
  7. BobK

    Digital display

    No, I don't have experience except for using off-the-shelf displays. I am still not sure what you are trying to do. If you can get hold of a replacement LCD, is it just installing it that you are having trouble with? As Kelly's eye says, making a custom display is not something easily done...
  8. BobK

    Odd Behavior of Circuit

    Assuming that those are the leads coming out of the bell, that is not the correct connection for the diode. The diode must be directly across the electromagnet coil in the bell. The way you have it wired, the diode is out of the circuit when the interrupter disconnects the magnet and the EMF...
  9. BobK

    Small dc motor speed control

    The point is that this topic is more complicated than you can address in a forum post. You will have to do some research on this before you even know enough to get help here. Once you have read up on it, we will be happy to answer questions. Bob
  10. BobK

    Digital display

    I take it you cannot get a replacement part? Is this a custom display, as many small LCDs are? Bob
  11. BobK

    Small dc motor speed control

    Let me google that for you Bob
  12. BobK

    Electronics help

    No. 300 / f = w multiply both sides by f 300 = w * f now divide both sides by w 300 / w = f Where w is in meters and the result is in MHz. For a 4 cm track to be 1/4 wavelength, the wavelength would be 4 times 4 cm. w = 16cm = 0.16m 300 / 0.16 = f = 1875 MHz or 1.875 GHz That would...
  13. BobK

    Need help testing this circuit

    Did you adjust the pot? Those voltages should change if you do so. Bob
  14. BobK

    Need help testing this circuit

    The phototransistor will not have a base connection. The light input acts like the base. Bob
  15. BobK

    Vishay resistor query - Red Black Gold Gold?

    Can't tell you how many times I have done a quick correction like that! Bob
  16. BobK

    Vishay resistor query - Red Black Gold Gold?

    I saw what you did :) Agree now, 2Ω. Bob
  17. BobK

    Continuous power vs timed charging for remotely deployed smartphone

    I think ypu have it backwards. It would be better to power it continuously. Once the batteries are charged, they will not draw any further current, and all of the power for the phone will come from the power bank. If you cyclically charge and discharge the batteries, you are wasting about...
  18. BobK

    Cooling electronic circut ?

    50C is not anything to worry about. Hell, in Phoenix the outdoor temp goes that high! Bob
  19. BobK

    Cooling electronic circut ?

    How hot? Can you hold your finger on the chip without burning it (the finger that is)? Bob
  20. BobK

    Odd Behavior of Circuit

    Why not just add the diode and see if it solves the problem? The original use of the bell probably did not incorporate any electronics, and a diode was unnecessary. Bob
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