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  1. BobK

    The smallest 240vac to 12vdc power supply

    If the only thing you are powering is a 5V PIC, why would you use a 12V supply? That is just wasteful with no advantage. Use a 5V adaptor. The one Amazon supplies with Kindle looks like a sightly large wall plug. Bob
  2. BobK

    low input to microcontroller

    I can think of many ways to do this. 1. Use the ADC. With a 5V reference, 200mV would read 10 counts. Accept anything above 5 as high. 2. Use the analog comparator built in to your microcontroller to test it. Put a reference voltage of 100mV (from a divider) on the - input and your signal...
  3. BobK

    How to strip the insulation off 3 core main cables?

    Has anyone mentioned teeth? Bob
  4. BobK

    why we need Load resistor?

    Yes, in fact, he argued that if the output impedance was less than 8 Ohms, putting a resistor in series with the speaker would increase the power delivered to the speaker! Bob
  5. BobK

    Transistors

    For the second time, this one: You are using a roughly estimated Vbe, then calculating the bias based on the current Ib. This is what Steve are I are calling a current control model. As Steve has also said, this step, if using a voltage control model, should be to calculate the exact Vbe...
  6. BobK

    Transistors

    Show me your design procedure then that does not refer to controlling the Ib. Once you have done that, you have embraced the voltage control model. Bob My bolding. Yes, and that is exactly why the designer treats the BJT as a device controlled by current rather than voltage. Bob
  7. BobK

    why we need Load resistor?

    Yes, I challenge anyone to show how their audio amp with an 8 Ohm output impedance transfers more power to an 8 Ohm speaker than my 0.1 Ohm output impedance amplifier. Bob
  8. BobK

    Transistors

    I don't think we disagree, you just seem to want to label current control as voltage control. From your post: How is that not using a current control model? If you were using a voltage control model, it would read: * Calculate two resistors for proper base DC biasing - based on a the exact...
  9. BobK

    Help charging lead acid battery

    Turn the voltage up until you get 1A anyway. At 1A it should charge enough for a start in a couple of hours. Bob
  10. BobK

    why we need Load resistor?

    Of course some chemistry batteries will catch fire if you try this. Bob
  11. BobK

    Transistors

    +1 on Steve's posts. I was trying to formulate how to say the same thing. Yes, the current in the base and the collector is controlled by a voltage (Vbe). But to a circuit designer this is, in most cases, useless. It is exactly the equivalent of trying to control the current through an LED...
  12. BobK

    Pill box

    Check this out, there are others as well. I Googled "Pill dispenser with alarm". http://www.amazon.com/Med---lert-Automatic-Dispenser-Times/dp/B002TSHGIU/ref=sr_1_1?ie=UTF8&qid=1397401723&sr=8-1&keywords=pill+dispenser+with+alarm Bob
  13. BobK

    capacitor polarity in a phono stage project

    You have a short. You may or may not have damaged some of your components. Bob
  14. BobK

    capacitor polarity in a phono stage project

    Many years ago, Popular Electronics tested to see if audiphiles could tell the difference between their beloved tube amplifiers and a good solid state one. Sure enough they could tell the difference and they all picked the tube one as sounding better. Then they (PE) analyzed the outputs of the...
  15. BobK

    Remote Control Circuit with CD4017 - counter decoder

    The 4017 is configured to be in 1 of 2 states. Each press of the remote causes a pulse on the clock, which swithes it to the other state. I.e. one press ON next press OFF. Bob
  16. BobK

    Transistors

    Yes, check out the first entry in the thread "Book Reviews" Bob
  17. BobK

    Transistors

    Voltage gain or current follower. I have never used that configuration. Bob
  18. BobK

    555 simple oscillator not working with small capacitors

    Yep, they must be using a 555 in the Flight Data recorder for MA370. Expected frequency 37.5KHz, detected 33KHz. Bob
  19. BobK

    Transistors

    Common emitter. Bob
  20. BobK

    555 simple oscillator not working with small capacitors

    There are very cheap multimeters that can measure frequencies. One of those would be fine for your project. Bob
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