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  1. BobK

    Logic family selection

    GPG just did give you a solution, why are you asking again? Bob
  2. BobK

    where do you get your "stuff?"

    1. Most parts are so inexpensive that it does not make sense to try to salvage them. 2. For many parts, I need an inventory of many different values, and I would never fill that by salvage. 3. For the parts that are expensive, you most likely will not find them in salvage. Take resistors for...
  3. BobK

    LED strip PWM problems

    The problem is that the response of the eye is logarithmic. It sees 1% duty cycle as probably 10% brightness. You need to use higher resolution. I have a color changing LEDs that use 256 levels, and they still have noticeable steps at times. I also have another with 4096 levels and this one...
  4. BobK

    where do you get your "stuff?"

    I use Mouser. They ship the same day and I get my :"stuff" in typically in 2-3 days via U.S.P.S. And Ebay for bulk orders common things like LEDs and transistors, resistors. Bob
  5. BobK

    Selector Button

    This can be done completely in software, no need to add an external counter. You need to do the following: 1. Learn how to de-bounce a switch in software. 2. Make your program check for a new push of the switch periodically, with the period being 1/10th of a second or so. 3. Keep a variable...
  6. BobK

    Differential amplifier

    The LM358 cannot reach 0V when driven by a single supply. It has a miniumum output of something like 40mV. Since the voltages you are trying to get are in that range it is not suitable. However, you still should not have gotten a voltage of over 1V for the case you mention. Did you actually...
  7. BobK

    My First Circuit Board Design - Will this print out well for a transfer?

    What is the width of your traces and the minimal spacing. I would not go for less then 15/1000 in (or 0.4 mm) on either of these for a first attempt. Bob
  8. BobK

    Differential amplifier

    You have not told us what wrong output you are getting with what inputs. And you have not answered the question about whether you are using a split supply. How do you expect us to help? Bob
  9. BobK

    Portable USB phone Charger Design Help

    Look at my post again. "As long as you have a 5V regulator" is that condition for everything that follows. Even a beginner can make a 5V regulator work. Bob
  10. BobK

    Portable USB phone Charger Design Help

    And to the OP. A charger using a 9V or 2AA will charge the phone less than 1 time for a set of batteries. There are inexpensive "power banks" available on Ebay that will charge it 4 times or so, and are rechargeable themselves. Something you build will cost you as much and be far inferior. Bob
  11. BobK

    Portable USB phone Charger Design Help

    Really? As long as you have a 5V regulator you are not going to destroy a phone or explode any batteries. The charging algorithm is built into the phone, all the phone needs is a 5V constant voltage supply. The only other consideration is how much current it will draw. Different phones will...
  12. BobK

    Do I need resistors with my transistor?

    For a saturated switch, my rule of thumb is base current 10% of collector current. Collector current is what the solenoid draws. Call it Is. Then it is simply Ohms law from there. The voltage across the base resistor is the voltage you apply to it -0.6V, the approximate Vbe. So: Ib = Is /...
  13. BobK

    Help With Correct Power Supply

    Motors take more current when they start or if they stall. The power supply you linked has enough power to run the motors but perhaps not enough to start them all at the same time. I would go with a supply capable of 10A. Bob
  14. BobK

    Audio Through Relays

    What you need is analog switches. Google it. Bob
  15. BobK

    Do I need resistors with my transistor?

    Yes, you need a resistor. The base emitter junction of a transistor is a diode. There is nothing to limit the current (except the internal resistance in the Arduino,) Here is a resource that explains it all...
  16. BobK

    Another transistor discussion

    Well, since there are no external components, it would just sit there looking pretty. You have to connect the terminals to some voltages (often through resistors) before it does anything. The external components do not change the physics of the transistor, they just set up the conditions under...
  17. BobK

    Connect 24V 2wire sensor to 5v Logic

    Sorry, I don't have any experience with that kind of sensor. That said, I think you could put a voltage divider from the brown to the blue wires, using resistors >> the series resistor, which should be set to something like 1K. So maybe: brown -> 10K <--> 2.5K -> blue Then take the signal...
  18. BobK

    Weird Meter Problem!

    If it is accurate it's a fluke! Bob
  19. BobK

    Help rebuilding High School project

    That is why we have to own them first. Bob
  20. BobK

    12vdc ground isolation

    If you expect any more help, you will have to show us a schematic. Your last statement does not make any sense. You cannot have isolated grounds using only 1 power source. Bob
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