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  1. BobK

    Mains electricity to circuit board

    Like this: The LED is the input of the optoisolator. The capacitor is sized for 120V 60Hz and a 20ma LED, if different you need to resize it. Bob
  2. BobK

    Help using TIP42c

    This should do it: R3 represents the bulb. Bob
  3. BobK

    Mains electricity to circuit board

    Use an optoisolator with a capacitor to drop the voltage to the LED side of it. Be sure to also bypass the LED with a diode pointing in the opposite direction. You should see a 50/60 Hz square wave out when the lines voltage is on. Bob
  4. BobK

    Power amplifier

    So another, much cheaper, option is to build a regulated power supply and use the 1-5V signal as the reference. Here is a supply design that would be suitable: http://ludens.cl/Electron/Ps20/Ps20.html You would just take out the zener based reference that goes to the - input of the op...
  5. BobK

    Power amplifier

    On second thought, you need to answer Steve's questions as well. If the signal only changes slowly, perhaps a voltage controlled power supply is the answer, and if it changes too rapidly (1MHz or higher) even an opamp solution will be very tricky. Bob
  6. BobK

    Power amplifier

    Basically, you need a high power opamp. They exist, but they aren't cheap. High Power Op Amps at DigiKey Alternatively, you could try to make it yourself, using a normal power opamp and a push-pull power darlington output stage. Bob
  7. BobK

    5V battery usb battery to 12V screen

    If you have 12V available why do you want to convert it to 5V then back to 12V? Bob
  8. BobK

    Power amplifier

    In addition to what Steve asked, Is the signal either 0V or 5V (digital) or anywhere within that range (analog)? Bob
  9. BobK

    Anybody here from Indianapolis???

    Got my masters degree at Purdue, but haven't been back since. Bob
  10. BobK

    Woo-Woo high output dc square wave generator help

    ROFL Yes, it is proven. And part of the proof, I hope you understand, is that the hydrogen produced contains less energy than you put in to produce it. Bob
  11. BobK

    How long should antenna wire be to receive amateur band?

    Though you can use it as an amplifier after the detector. Bob
  12. BobK

    Want circuit to return to previous state when turned back on

    duplicate
  13. BobK

    Want circuit to return to previous state when turned back on

    The PIC16F1826, 1827 or 1847 are cheaper and more capable than either the 16F84A or 16F228A. Each new generation adds capabilities and decreases the cost. The 18xx are the latest chips. Bob
  14. BobK

    Watchdog Timer

    If you are using C, all variables are likely to be re-initialized. For assembler, not so. In C there should be a way to avoid the re-initialization. You would have to look at your compiler documentation. But anyway, as both gorgon and I have pointed out, this is a silly use of the watchdog...
  15. BobK

    Voltage amplifier- DAQ

    An opamp is definitely the way to go. Google opamp non-inverting amplifier. All you need is two resistors to set the gain. If you want to use a single supply, be sure to get an opamp with rail-to-rail inputs and outputs. Bob
  16. BobK

    Watchdog Timer

    Yep, set it for 2 seconds, and each time it fires, increment a variable, which was initialized to zero. When the variable reaches 10 light the LED. However, that said, that is it the typical use of the WDT. You could use normal timing techniques for that. The WDT is typically used for 1...
  17. BobK

    Help required with placement of diodes on electromechanical vane display

    Deleted, I was wrong here. Bob
  18. BobK

    Want circuit to return to previous state when turned back on

    It may seem like overkill, but a microcontroller could do this and replace all your logic gates as well. Bob
  19. BobK

    How long should antenna wire be to receive amateur band?

    No wonder they are called Stratocasters. Bob
  20. BobK

    Help required with placement of diodes on electromechanical vane display

    Unless I am misunderstanding something, the diodes are there in the chip. Bob
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