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  1. BobK

    Resistor Trouble

    Which is why I didn't bother to answer that. Bob
  2. BobK

    LED Light Tower Design

    And if you want all sides illuminated, probably 4 strips, one facing each side. Bob
  3. BobK

    Potentiometer Value and Rating?

    Yep, our studio wants us to compete, which can cost about $4000 for one competition. Not to mention the price of the ballroom gown (for Morticia, not me.) Bob
  4. BobK

    Resistor Trouble

    You are confusing battery capacity mAH with current mA. They are not the same thing. The battery capacity (mAH) tells you how many mA you can draw from the battery for 1 Hour before it is exhausted. Ohm's law tells you how much voltage is dropped when a given amount of current flows...
  5. BobK

    Soldering and veroboard HELP!!

    The principle is quite simple. To solder two pieced of metal together, put them in contact, heat them with a soldering iron until they melt the solder on contact. Do not melt the solder on the iron, melt it on the things you are soldering together. But, you do need to use the right kind of...
  6. BobK

    clock charing usb devices

    Did you look at that video? He produced 21 Watt Hours of energy over about 2 minutes to toast that piece of bread. How much does it take to charge a typical cell phone? 1A at 5V = 5W for about 2 hours, so 10 Watt Hours. That is about half of what the cyclist produced. If winding your...
  7. BobK

    LED monitoring

    Then, as Hevens says, the pin that is driving the LED is already a digital signal. High for off and low for on. Bob
  8. BobK

    Soldering and veroboard HELP!!

    I never do any of those cleaning things, and I have no problem soldering. My first question would be what kind of solder are you using? Bob
  9. BobK

    Inverter 12V to 220V

    You are going to use a 12V solar panel and an inverter for heating? A glass window is much more efficient. Bob
  10. BobK

    Student Helmet Project

    If the Arduino requires 34mA in sleep, it is not usable on this project. My favorite small PIC microcontroller 12F1840, running at 5V, uses 600μA at 4MHz, 3.4mA at 32MHz and as little as 6μA in sleep mode. Of course I would run it at 3.3V off the LiIon battery, at which it draws even less. It...
  11. BobK

    Potentiometer Value and Rating?

    That explains why my dance lessons cost so much! Bob
  12. BobK

    Inverter 12V to 220V

    Take the same precautions you would in dealing with 220V house wiring. Bob
  13. BobK

    Potentiometer Value and Rating?

    I presume the load is some kind of a heating element. Use PWM to control the power to it. Bob
  14. BobK

    Solar Powered Speaker

    Also, consider that an amplifier rated at 15W will draw about 30W to output 15W, unless it is a class D. I would definitely look for a class D amp. These would run maybe 17W to output 15W. Bob
  15. BobK

    configuring 3 power supplies in parallel

    Using diodes to share the current is not the best way. If you are going to do so, resistors work better. Why? Because a resistor will respond linearly to drop the voltage based on current whereas the diode responds logarithmically. Thus the resistors adjust down the voltage of the highest...
  16. BobK

    LED Circuit for STEM activity

    Why would you bother with logic gates, when you will need switches anyway, and switches can do the entire job themselves? Bob
  17. BobK

    Instability on a diferential output amplifier

    Sorry, I substituted the 4.7V zener for the 24V Zener in my head. I now see that is rail is 24V. But what I said about the dissapation still applies. I think if there is any heating of the differential pair you are going to get drift problems. Is there any reason you cannot lower the current...
  18. BobK

    Instability on a diferential output amplifier

    Looking at it again. Here is my analysis of the differential pair's operating point: The voltage at the emitters is about 4.7 - 1 diode drop or 4V. The voltage at the collectors is about 60 - 3 = 57V. The current through the transistors is ~6mA. So we have them dissipating: P = I V =...
  19. BobK

    LED Circuit for STEM activity

    A simple SPDT swich for each pair will do. If you want to get really fancy, there are LEDs that will light red with one polarity and green with the opposite polarity. These could be handled with s DPDT switch for each LED. Bob
  20. BobK

    Instability on a diferential output amplifier

    I don't have an answer, so I will ask some questions. Why are the collector resistors for the differential pair connected to +60 instead of the ~55V regulated rail? Are the differential pair matched and kept at the same temperature? The 1K collector resistors seem like they are too low. You...
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