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  1. BobK

    EL wire inverter help needed

    I am curious as to why you would want them to stay on when not powering anything. What does this accomplish, other than wasting battery energy? Bob
  2. BobK

    3 watt LED mounting..

    You really don't want to running a 3W LED by connecting it directly to a 3.7V Lithium battery. You need a constant current source. Bob
  3. BobK

    Adding a timer to a stereo amp

    <Puffs up chest> Bob
  4. BobK

    Adding a timer to a stereo amp

    The mic input is not the best one to use for this. Is there an aux input you could use instead? That input would be better for the level coming from the timer's beeper, and would be less likely to pick up a hum. Bob.
  5. BobK

    Clearing doubts on grounding electronics circuitry

    Circuits can be isolated by using a transformer or an optocoupler. In these cases there is no electrical connection between the two circuits and the signal is carried across by magnetic field or light. If you want an electrical connection, there has to be a common ground. Otherwise, the...
  6. BobK

    ws2812 RGB led project

    Individually addressable is quite misleading. These devices act like a shift register with 24 bits per LED. To change any particular pixel, you have to transmit all the data for the entire string. So, for a string of 50, you would be sending 1200 bits of data. Bob
  7. BobK

    Ordering PCB's help for my first design and order...

    Single sided does not necessarily mean components on both sides. It means traces on both sides. Edit: On that calculator the first total is the price the second is the price + shipping, so it is not as bad as it looks. Bob
  8. BobK

    Ordering PCB's help for my first design and order...

    Since you mentioned it, most PCB houses will not charge any difference for single sided vs double sided boards, so you might as well go double sided. If you are not familiar with it, all the holes are automatically plated through so that top and bottom connect to each other. Layout is much...
  9. BobK

    Measuring peak voltage of square wave - ATmega328p

    The ADC will not measure an average voltage, it samples quickly and then measures that instantaneous voltage. To get peak voltage, you would sample maybe 8 times in one period and then just choose the highest. Bob
  10. BobK

    How to Step up Voltage? DC to DC converter or Op Amp

    A 741 is a terrible op amp to use with a single 9V supply. Its output voltage range will be from about 2 to 7V. Use Kris's circuit and add a rail-to-rail single supply opamp as a voltage follower. Bob
  11. BobK

    Charlieplexing using the Arduino Uno?

    The OP said 21 characters, and he laid out the design and came up with 205 LEDs. This says to me that he is making up the lines of each character with LEDs. He said he wanted it to blink in sequence, whatever that means, perhaps on letter at a time blinking off? Need more info. Bob
  12. BobK

    LED lighting without power source

    I would be careful around coils of wire at you house! Bob
  13. BobK

    Please Design This PCB...

    I think shilon is one of those who think that if you teach him how to fish, he will have to work the rest of his life. Bob
  14. BobK

    Charlieplexing using the Arduino Uno?

    Can you refine your description, because it does not sound to me like you need to control the LEDs individually. Bob
  15. BobK

    LED lighting without power source

    I think you have answered your question. Is there a reason you did not include this info in your first post? Bob
  16. BobK

    Alarm when handbag opens accidentally

    Well, you could make it more complicated by having the handbag send you a text message when it comes open. I believe this is called the "internet of things". Bob
  17. BobK

    Help, Thermal Switch for Shower Exhaust Fan?

    That thermal switch is designed to switch line voltage (in the U.S.), but I can understand your hesitance to put line voltage on it. You can use a transformer or wall wart to lower the voltage then use a relay to turn the fan on. You want the automatic switch and the manual switch in parallel...
  18. BobK

    Help for hooking radio speaker to 3.5mm headphone jack

    Mixing the two signals simply means putting a resistor (say 10K) between each and the input to the amplifier, it is no big deal. Bob
  19. BobK

    Fun and games with autotransformers

    In my defense, I actually took much less time than that to figure it out, but them kept messing up my calculations to check it. Bob
  20. BobK

    Primer on Transformers needed

    Hmmm. Try taking the primary off a power transformer core and plug it into your AC outlet. What will happen? Bob
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