Search results

Search Forums New Posts
  1. BobK

    Help rebuilding High School project

    Did your project light the lights in the same pattern as you see the spots on a die, or did it just have 6 lights to indicate 1 through 6? The circuit Martin posted does the latter. I would prefer the former if I were building it. If you want to update to the modern world, a microcontroller...
  2. BobK

    9v batter to 2 servos

    A breadboard is just a different way of connecting components together. Whether they are wired on a breadboard or by wires, makes no difference in how the circuit operates (at least not at low frequencies). You seem to have no understanding of how serial and parallel circuits work. Please...
  3. BobK

    How to keep 7805 from overheating?

    Don't Arduinos have a built in regulator? Bob
  4. BobK

    Audio transformer for crystal set help

    Clearly it does not need a center tap since the center tap is left unconnected! Bob
  5. BobK

    I need help building a solenoid controled by a rheostat

    Okay then, it sounds like you want to vary the force on the solenoid, not the position, so a linear actuator would not be appropriate. Why 33 in long? That sounds rather huge for your purpose. Can you explain in more detail what the mechanics look like? Do you have a drawing of your design...
  6. BobK

    Connect 24V 2wire sensor to 5v Logic

    Link to the datasheet? Bob
  7. BobK

    Another transistor discussion

    Only by accident :) (Gee, this transistor does not seem to have enough gain o_O) Bob
  8. BobK

    Another transistor discussion

    Actually, even that is not true. Try connecting the base to 5V through a 1K resistor, the collector to ground and the emitter to +5V. Now the equation is: Ic = Ib + Ie Bob
  9. BobK

    Weird Meter Problem!

    Well, the errant reading was across a 4.7K resistor, so the high input impedance answer is moot. Bob
  10. BobK

    Another transistor discussion

    I agree that he was confused about the relationship of base current and collector current. But I still disagree that "what goes into the base comes out the emitter" is false. Just because there is also current coming from the collector out through the emitter does not make that statement...
  11. BobK

    IR Sensor

    You have seen it. It is called the Segway. Bob
  12. BobK

    Does a breadboard supply the same amount of power to everything connected

    Yes, you could do that, but it would not supply the correct voltage to the servo. Using a resistor to reduce voltage will work only if the device draws the same amount of current always, like an LED. A servo will draw much more current when the motor is running than when it is stopped. So, if...
  13. BobK

    Another transistor discussion

    I did catch it, but you has posted the correction before I got a chance to, damn it. Not trying to argue here, but why do consider "current from base to the emitter" to be an inaccurate description of Ib, at least for an NPN transistor using conventional current? Surely all the current flowing...
  14. BobK

    I need help building a solenoid controled by a rheostat

    What are you trying to do? Are you going to try to control the position of the solenoid by controlling the current? This will not be very efficient or accurate. A better solution might be a linear actuator, which is a motor and gearing that move in a line. Bob
  15. BobK

    Optoisolator

    I would second AnalogKid's solution. Bob
  16. BobK

    12v to 5v

    Then you have little hope of driving them correctly. Using the 12V power is actually more efficient than reducing it to 5V because you can put several LEDs in series and reduce the total current you draw. You need to determine the forward voltage and current that the LEDs are designed to...
  17. BobK

    Mixing Woodworking and Electronics

    I have no experience with Hakko. Once again, my experience going from a good brand (Weller) non-temp controlled iron to a no-name brand temp controlled one made me realize how important temp control is. The Weller was hit or miss whether the temp was right or not. The temp controlled one is...
  18. BobK

    Use a ground pin as a switch

    Link me to a datasheet and I will answer. But, I need to know how much current the sensor you are using requires. Bob
  19. BobK

    gain amplifier

    For a gain of 2 you need equal resistor for feedback and to ground. An LM324 should work okay as long as the supply is 2V greater than the max output you need. Here is a simulation. Note that below about 100mV the output will not be accurate because the op amp cannot output all the way down...
  20. BobK

    Use a ground pin as a switch

    This circuit should do it. It can handle up to 500mA. Choose resistor R2 so that it passes 1/10th of the desired collector current. The formula is: R2 = (3.6 - 0.6) / (Ic / 10) Where Ic is the current needed by the device. Bob
Top