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  1. BobK

    a circuit equivalent to function generator

    Or a Colpitts oscillator, which has a single transistor, inductor and a few capacitors and resistors. Bob
  2. BobK

    a circuit equivalent to function generator

    Oscillator + audio amplifier. Bob
  3. BobK

    Electronic Metronome

    If you want to set it digitally, a microcontroller is the way to go. But I don't see what is your problem with an analog pot. If calibrated it should be accurate enough. I don't think you will be able to tell the difference between 100 and 101 beats per second. An old fashioned metronome was...
  4. BobK

    supercapcacitor based battery

    What is your application? In most cases batteries are a better choice. Bob
  5. BobK

    How to turn off a LED with 3.7v

    As 2 other people have already suggested, you can leave the diode out in Dorke's circuit and it will work just as well. And there is an even better solution. Use a normally closed pushbutton in series with the LED, resistor and battery. Pushing the button then breaks the connection and the...
  6. BobK

    motor reverse

    You want to match the speed (RPM) and torque of the original motor. Bob
  7. BobK

    Transistor as a constant current source to variable DC input

    The Zener will always drop about 4.7V at 32 V input the current through it is: V = I * R I = V / R I = (32 - 4.7) / 1000 = 27mA At this current it will dissipate 4.7 * 0.027 = 0.127 W or a little over 1/8 W. A 1/4 W Zener is appropriate. The circuit works by controlling the voltage across...
  8. BobK

    latching pushbutton help

    If your range is 50 to 200 RPM you should use a gear motor that already has a max a little above 200. Slowing down say a 3000 RPM motor to 50 RPM will not be optimal. The gear reduction means a motor with much less torque (hence smaller, cheaper) can be used, because the torque increases in...
  9. BobK

    Transistor as a constant current source to variable DC input

    Here you go. D2 is a 4.7V Zener diode. This will regulate the current to approximately I = (4.7 = 0.7) / R In this example I used 20mA and, as the graph shows, the current varies from 19.59 to 19.89 mA. At this current the transistor is dissapaing (32 - 4 - Vf) * I. For a red LED at Vf...
  10. BobK

    newbie question

    100 lights per set and run off a single 600mAH battery? Impossible. Bob
  11. BobK

    Small LCD Display

    Most likely, more than you are capable of. A microcontroller is not capable of doing an animated video. You would need a full blown processor, like an ARM for that. Raspberry PI is a good example. There are LCD screens already interfaced to it. Bob
  12. BobK

    Need help with school project; photocell, op amp, and 555 timer

    The op amp cannot provide enough current for the relay. I would suggest configuring the 555 as a monostable and using the opamp to trigger it. Bob
  13. BobK

    newbie question

    There are many things wrong with what you are proposing: 1. These are likely NiMH batteries and they can be overcharged and vent, though they will not likely catch fire. C/10 is too high to trickle charge them, C/20 is recommended for trickle charge of this type of battery. 2. Putting 5...
  14. BobK

    Voltage and light bulb

    Lower voltage will result in lower current. Power is voltage times current, so lowering the voltage will lower the power by the square of the voltage ratio. I.e. if you use 1/2 the voltage you will get 1/4 the power. This is only true for resistors, though. A light bulb (incandescent) has a...
  15. BobK

    Sensor interface, OP AMP, -500mV +500 mV to 0-5 V amplifier

    Whoops, I meant output, not input. For the popular LM324 single supply opamp it can only go to about 40mV. Bob
  16. BobK

    self-walking legs

    Get a powered wheelchair. Bob
  17. BobK

    Building an EMP, having difficulties

    From its Fourier components? Of course the infinite frequencies required is a drawback. Bob
  18. BobK

    Whatever happened to the Speech recognition chip?

    Did you try Ebay? You can often find discontinued chips there. Bob
  19. BobK

    parallel led array

    OK, don't blind any ghosts, though! Bob
  20. BobK

    Sensor interface, OP AMP, -500mV +500 mV to 0-5 V amplifier

    Okay, I missed that Adam. Bob
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