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  1. J

    LDR Motor Circuit

    I think the 15k resistor is to high. It forms a voltage divider with the 1k resistor. The lower the R2 value in a voltage divider the lower the divided voltage. You need less then .7V on the base of the transistor. Measure the output voltage on the output of the 741. Select a base resistor...
  2. J

    LDR Motor Circuit

    Not that it matters, but you can use one 50k ohm pot and combine the two resistors and pot into one package.
  3. J

    pwm to control a dc motor

    speed is directly related to the voltage seen by the motor. If you always put 3V across the motor it will run at the same speed regardless of anything else. When you use PWM, the duty cycle ON time determines what voltage the motor sees. It is always a percentage of Vcc. IE, if you have 12...
  4. J

    seemingly impossible class project

    Seriously, he has a 6V battery with 3mA output, that wouldn't even leave a tingle on the end of a human nerve. Relax a little!
  5. J

    current division in circuit

    Looks good to me.
  6. J

    pwm to control a dc motor

    example: If you pulse 12V to a motor with a duty cycle of 60% on time, then the motor will only see 7.2V
  7. J

    pwm to control a dc motor

    The current gain of the 2n2222A is 40 @ 500mA Ic, refer to the datasheet here http://www.uib.es/depart/dfs/GTE/staff/jfont/InstrETT/2n2222.pdf 0.3A/40 = .0075A of base current needed. Double this number, because a little extra won't hurt. so then you take the 555 output voltage, which you have...
  8. J

    pwm to control a dc motor

    How much current does your load use? What is the gain of the transistor? This will tell you what you need for base drive current of the transistor. Then you can use ohms law and figure out the resistor value needed for R1. Why exactly are you using R?
  9. J

    LDR Motor Circuit

    doubly agreed
  10. J

    Define your own semiconductors

    Do you work for EBV or what? This totally seems like commercial advertising.
  11. J

    Newbie: Starting out with electronics...breadboards

    http://www.ehow.com/video_2372554_learn-double-pole-switch-circuit.html if you have a multi-meter you can figure out which two pins are electrically connected using the Ohms feature of the meter.
  12. J

    LCD Monitor cable connector - Identification

    Photo link does not work, please fix it so we can maybe help you
  13. J

    Heat Generation

    I got a horse, but I am missing how this works. What is the point of the perforated metal tube exactly? Got a link that explains this?
  14. J

    seemingly impossible class project

    Even though I can't really tell you how to do it, what I do know is Ohms law is important in all electronic circuits. Knowing this, one would have to assume that since you need to deliver a constant current and the resistance is ever changing, then you need to build a circuit that can vary it's...
  15. J

    LDR Motor Circuit

    the collector current for a BD139 is 1.5A, that should be plenty for that motor. It could be heating up because you are running the transistor in its linear region. What exactly is the motor running?
  16. J

    Capacitor & Inductor

    I don't think you understand. When a capacitor first charges the voltage across it's two leads is zero (short circuit). When a DC voltage is applied across the capacitor it starts to charge. The voltage across the two leads and will increase till it reaches the voltage applied to it. When the...
  17. J

    introductions

    what exactly is a FOG? I got my assumptions, but better hear it from the horses mouth instead. welcome dick!
  18. J

    where did resqueline go?

    Yeah, hope so to. Let's just hope it is late summer and he is just out and enjoying the weather.
  19. J

    Capacitor & Inductor

    "Under a dc condition" means a stable voltage. An ideal capacitor has zero current flowing through it (acts like a open switch, open circuit) when the voltage across it is the same as the DC voltage source. An ideal inductor is nothing more then a wire. Once charged, The inductor still acts...
  20. J

    LDR Motor Circuit

    What is the output voltage of the op-amp with the pot. at zero and the LDR is dark?
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