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  1. BobK

    From batteries to Wall power supply

    Can you disassemble the device a bit more? To where we can see the wires coming from the battery compartment. Bob
  2. BobK

    Amplifier?

    What was the actual assignment? Because I would not consider using an LM386 as "making an amplifier" . Bob
  3. BobK

    Novice needs help with three phase motor controller

    Or you could put back to back electrolytics to make a non-polarized cap. Bobs
  4. BobK

    Servo controlled by Potentiometer

    A servo cannot be directly controlled by a potentiometer. The pot has to change the width of pulses sent periodically to the servo. The simplest circuit to control a servo would be to use a 555 timer chip. You can look this up on the net and find circuits to do it. Your switch would have to...
  5. BobK

    Wireless Voltmeter probes?

    I have to disagree with the other posters. If there is a common ground between the two circuits, it could be done. In this case you would be reading each voltage WRT ground, then subtracting them to get the voltage WRT each other. Bob
  6. BobK

    LED bulb design- how to find luminance

    Since that chart is showing relative luminance, take the ration of the reading from the chart at 30 divided by the reading at 65 and multiply by 32 lumens. It looks like 1.0 at 65 mA, and about 0.5 at 30mA so, 1/2 of 32 or 16 lumens. Bob
  7. BobK

    Converting a projector from incandescent to solid state?

    Are you sure it is only 1000 Lumens? That is less than a 100W bulb and you say the bulb is rated at 500W. I would wonder why it would be so inefficient, particularly when heat is a problem with a projector. Bob
  8. BobK

    speed control problem for helicopter

    ESC (engine speed controller?) There must be some input to the ESC that determines the duty cycle of the PWM out. That is where you would intervene. Bob
  9. BobK

    Decoding signal

    I see. There is nothing about the protocol except that the frequency is 433MHz. It could be quite difficult to decode it without even knowing how the bits are encoded. I am not an expert on RC protocols, perhaps someone who knows more about it could step in. Bob
  10. BobK

    speed control problem for helicopter

    You need feedback of the rotor speed to control the PWM signal. A rotary encoder of some kind or a hall effect sensor is typically used to do this. The sensor will produce N pulse per rotation. Then what you have to do is count these to get the speed (or more likely the time between pulses)...
  11. BobK

    Multiple power supplies (many stages in project)

    The Arduino is going to have a 5V regulator, and, assuming you do not need too much power, you could power your other 5V circuitry from it. The same with the 9V, just make sure there is enough power for everything. Bob
  12. BobK

    Resistive Load and Battery Life

    Yes, with the same current through the batteries internal resistance and the external load, the one that drops more of the voltage (i.e. the higher resistance) will dissipate the most power. Bob
  13. BobK

    Resistive Load and Battery Life

    Okay, you asked for some math. Let's do it by example: You have a battery that is 10V and internal resistance 10Ω. ------------------------------------------------------ For a heater coil with 5Ω you would get: I = 10 / (5 + 10) = 10 / 15 = 0.667A Power in the heater is: 0.667^2 * 5 =...
  14. BobK

    Multiple power supplies (many stages in project)

    Are you sure you need +/- 12V for the filter? I am assuming opamp based active filters. There are many single supply rail to rail opamps that might work okay off you 9V or even 5V supply, depending on the range of the signals they are handling. Bob
  15. BobK

    Decoding signal

    Some info about the transmitter and receiver might be useful. Bob
  16. BobK

    PIC programming

    I would not recommend using PIC16F84 or PIC16F88. These are obsolete chips that are more expensive than newer, more powerful chips. For example, the 16F1847 has twice the program memory, 3 times the RAM, runs at 4 times the speed from the internal oscillator, has more peripherals and costs...
  17. BobK

    Resistive Load and Battery Life

    Matching the external resistance to the batteries internal resistance would indeed result in the most power transferred to the external resistance. But it is not likely that is what you want, since it would result in equal heating of the battery. What you want is most of the heat in the...
  18. BobK

    Connecting USB outlets in parallel for more current draw?

    Really, for any length? (100m of 30ga is 33.9 Ohms, not what I would call a "dead short") Bob
  19. BobK

    12 volt remote horn push

    Oh, didn't know what was allowed. How about this 433Mhz one then? http://www.ebay.com/itm/2-Channel-433MHZ-Wireless-RF-Remote-Control-Receiver-Controller-F-Car-Motor-BG-/151302448241?pt=Garage_Doors_Openers&hash=item233a542471 Bob
  20. BobK

    12 volt remote horn push

    If you want cheaper, you can get them on Ebay: http://www.ebay.com/itm/DC-12v-10A-relay-1CH-wireless-RF-Remote-Control-Switch-Transmitter-Receiver-/381073666914?pt=Garage_Doors_Openers&hash=item58b9c2b362 Bob
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