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  1. BobK

    Number of batteries

    The simple way to calculate this is by using Watt Hours. The battery is rated at 8WH. You need 16V at 25A for 45 minutes. This is: 16 * 25 * 45 /60 = 300 WH Divide that by 8 WH per battery and you need 37.5 batteries. To make the math work out, lets you 40 batteries 5S8P. With 8P you need...
  2. BobK

    DC Voltage multipliers?

    b Yes, use a ruler and measure it in centimeters. Your question does not make any sense. Voltage multiplier usually refers to a circuit that takes in AC, runs in through a string of diodes and capacitors to produce a DC voltage that is a multiple of the input minus some diode drops. You can...
  3. BobK

    etching my first pcb's

    I will suffer 12 min exposures to avoid UV exposure problems. Bob
  4. BobK

    etching my first pcb's

    I think you will find a very long exposure time with an incandescent bulb. They do not produce much UV. A fluorescent bulb is much better. I use a 12 inch fluorescent about 8 inches from the board and have an exposure times of 12 minutes. Bob
  5. BobK

    pass transistor...

    Their outputs are connected to the output of the LM2940 regulator, so it will try to keep that output at 12V. If it goes low, the LM2940 will increase the current it outputs. This increases the voltage drop across R1 which lowers the voltage on the bases of the pass transistors causing them to...
  6. BobK

    motor and pumps use 2 x 115 v ac and this is problem

    The two phases in U.S. 230V are really not phases, they are 180 degrees, i.e. inverted from each other. When you place a device across the two "phases" it is equivalent to a 230V single phase system. You can use your 230V single phase power to directly power this. Bob
  7. BobK

    What resistor is this?

    Since people were not familiar with this notation, let me show you some more about it. If K or M is used as the letter, you use the same method to determine the value (position of the letter is the posltion of the decimal point), but you then multiply by 1000 for K and 1,000,000 for M. For...
  8. BobK

    What resistor is this?

    No, it is marked as 0.68Ω. When a résistance is given with and R, the R represents the location of the decimal point, so: 68R = 68Ω 6R8 = 6.8Ω R68 = 0.68Ω Surface mount resistors are always marked this way. Bob
  9. BobK

    Electric motor - one rotation then stop

    Yep, that is called ... engineering! Bob
  10. BobK

    Electric motor - one rotation then stop

    Yep, as I said in post #8. Bob
  11. BobK

    hi-fi audio signal booster- RCA input connections - how to wire the "shield" ??

    It sounds like the Bose unit is designed to connect to the speaker outputs. If that is so, why not connect it that way? Bob
  12. BobK

    Arduino, what is it ?

    The other thing about Arduino is that there are a large number of "shields" which are plug in boards that provide various hardware functions. For example, you could get a stepper motor shield and control a stepper motor from the Arduino. Basically, the Arduino is a solution for people who want...
  13. BobK

    Ground loop filter?

    I am probably out of my level of expertise here, but I will try a quick calculation: Basically, too few turns would look like a short on the input side of the transformer. Line level is nominally 600Ω impedance. You would want the impedance of the transformer to be around that high at the...
  14. BobK

    Ground loop filter?

    Sorry, I misread windings for turns! Bob
  15. BobK

    Ground loop filter?

    2 turns would be much to low impedance at audio frequencies. I don't know how many would be correct, but it would be a lot more than 2. Bob
  16. BobK

    BPW34 & Rail to Rail OpAmp

    Check Microchip. They have a good selection of rail-to-rail opamps that operate at 5V. Bob
  17. BobK

    Electric motor - one rotation then stop

    The stop switch would be a normally closed switch which opens when pressed. The start switch would be a normally open switch wired directly across the stop switch. When you press the start switch, and hold it long enough for the motor to move past the stop switch, it will then run until the...
  18. BobK

    Power over Ethernet

    44V is too much for most regulators. Bob
  19. BobK

    Home made speaker

    Here is a practical 1W into 8Ω class AB amplifier. It has < 1% distortion at 0.5V peak in and 4.0V peak out.
  20. BobK

    Home made speaker

    Your output transistors are wired incorrectly. The two emitters should be together and to the output. The collector of the NPN should be to V+ and the collector of the PNP should be at ground. Bob
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