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  1. BobK

    I need assistance on one way transmit

    I think you might be able to do this, but the two antennas might be considerably longer then 15 feet! The problem is that the 555 cannot operate a high enough frequencies and would be in the long wave band (below AM broadcast), which requires a long antenna due to the long wavelengths. Bob
  2. BobK

    Very compact voltage dropdown

    A CR123A 3V lithium battery comes to mind. No voltage conversion necessary. Bob
  3. BobK

    Piezo as a contact microphone

    Why not use a piezo contact microphone, which is designed for this purpose? https://en.wikipedia.org/wiki/Contact_microphone Bob
  4. BobK

    Synthesizer component parts

    Your PC sound card already has a quite capable synthesizer. What would this add? Bob
  5. BobK

    Question about B-E voltage.

    Once again all of the Vbe fans miss my point. Ib and Ic are related by a simple linear formula. I don't care whether one controls the other. It makes no difference when I design a circuit. In a small signal amplifier circuit, Vbe barely changes while Ib and Ic change over a wider range, due...
  6. BobK

    Help with an ultrasonic rangefinder for blind people

    Why do you think you need a Raspberry Pi? Are other microntrollers or embedded computers not capable of doing this? In fact, it can be done even without a microcontroller, though I would use one myself. Bob
  7. BobK

    Question about B-E voltage.

    I will say my piece, which everyone ignored last time, once again. If Ib is a function of Vbe, then we can write a function for the collector current in either Vbe or Ib, no matter which one is actually controlling it at the semiconductor physics level. They are equivalent as far as user...
  8. BobK

    12v curcuit connected to 24v PSU what will happen

    No. Ohms law is: V = I * R For the same resistance, double the voltage and you double the current, and, since: P = V * I You quadruple the power. Edited to add: But most circuits, including a simple incandescent lamp, are not simple resistances. For anything other than a resistor, the...
  9. BobK

    Replace fried range hood transformer with cheaper alternative?

    Yes, a 12V 5A transformer would be large and heavy. Bob
  10. BobK

    Please identify these resistors

    They look to me like: brown-green-yellow = 150K and blue-grey-black-silver = 6.8 But this makes no sense since paralleling a 150K with a 6.8 would basically have no effect. Bob
  11. BobK

    volume to liter conversion

    A liter is 1000 cubic centimeters. Bob
  12. BobK

    Changing LED colour in old hifi equipment

    I think our eyes are particularly sensitive to blue light because there is not that much of it in nature. I.e. a blue LED at the same power level will seem brighter than a green or red one. I had one on the my monitor at work, and it was so bright I had to tape over it. Bob
  13. BobK

    How to make a computer

    You are right. But it is not rocket science. Rocket science is a lot easier. The forum is not a resonable place to learn how to design a CPU. You need to do a lot of reading. Bob
  14. BobK

    Convert +12V DC to -30V DC

    Unless you are being extremely literal on the word "can't", there is not mistake here. Yes, you can supply it with ±30V, but the result will not be good. Bob
  15. BobK

    Oscillator or Not?

    Card carrying member of the James Randi Educational Foundation. http://web.randi.org/ Bob
  16. BobK

    Basic Amplifier

    Here is about the simplest amp that would reasonably drive an 8Ω speaker. It can deliver about 1/4 W before distorting noticeably. It has a gain of about 8 and is suitable for amplifying a signal from a headphone jack on a phone or MP3 player. To increase the gain, put a 220uF capacitor...
  17. BobK

    PWM LED THROUGH MOSFET

    I don't think it is the BJT that is causing the problem. It is the 100Ω resistance through which the gate must discharge. You need a two transistor driver (high, low side) so that there is less resistance for turn on and turn off. Bob
  18. BobK

    Basic Amplifier

    In order for a class A amplifier to driver 10W into an 8Ω speaker, you would need to change the collector resistor to about 8Ω, it would need a 36V power supply, and it would it would waste 80W when idling! So, no, you cannot reasonably modify your circuit to be a 10W speaker driving amplifier...
  19. BobK

    Changing LED colour in old hifi equipment

    Have not had a chance to check your work yet because we had a death in the family today. But I will take a look when I get a chance. One thing I can say, The voltage is actually 8, not 8.2. I don't know what the 8.2 means there, but there is not V after it like there is after the 8, and the...
  20. BobK

    Relays activated by timer 555

    You need a flip-flop and a couple of AND gates between the 555 and the relays. Each 555 pulse would toggle the flip flop. The two relays would be energized through an AND gate with the 555 output and Q of the flip-flop for the first one, and \Q of the flip-flop for the second one. Bob
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