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  1. BobK

    Electromagnets?

    Ferrite is the wrong thing for an electromaget, you want iron. I played with them when I was about 12. I would get basically really weak things, until I wrapped about 50 turns of house wiring (probably 14ga) around a piece of rebar and powered it by 2 D cells. It was quite powerful. The...
  2. BobK

    32 I/O Data Acquisition board architecture required

    Digital or, analog? Levels? Speed? Bob
  3. BobK

    Switch for oscillator (and some book recommendations too)

    Not sure how you are planning to get 3 levels that way. I suppose you could put the smallest capacitor on by default and have the other two positions add one in parallel. But it would be odd having the lowest value in the center. Bob
  4. BobK

    Digital Pot setup

    Here is what you need. You would have to have two debounced switches to operate it. http://www.analog.com/en/digital-to-analog-converters/digital-potentiometers/ad5220/products/product.html or http://www.maxim-ic.com/app-notes/index.mvp/id/1118 By the way, I found it by searching...
  5. BobK

    Need Advice RE Diode for Battery

    If the battery is in a device that keeps it charged, putting a diode in series will prevent it from charging! Bob
  6. BobK

    Current meter is burning out microcontrollers

    Disconnect the + terminal of the battery from the device. Put the multimeter in current measuring mode. Connect the red lead on the multimeter to the + terminal of the battery. Connect the black lead on the multimeter to the + lead from the device. This will not damage the device. All you...
  7. BobK

    using potentiometer in circuit

    A battery that can supply 2V at 10A can also supply 1.5V at 10A. You would put a resistor in series that would drop the 0.5V based on Ohms law: V = I R 0.5 = 10 R 0.05 = R So a 0.05 Ohm resistor in series with a circuit that draws 10A at 1.5V would let it operate off...
  8. BobK

    Basic transistor Guitar Amp

    Here is what I said way back. We are not in disagreement. And the circuit I posted is just one I use to drive a little speaker on my bench. It was not proposed as a serious guitar amp, I said it was "a guitar amp only your neighbors could love". I posted it as an exmaple of a push-pull...
  9. BobK

    Charging alkaline batteries

    It is not reccomended, but you can find info on the web about recharging alkaline batteries at you own risk. Bob
  10. BobK

    using potentiometer in circuit

    If you are measuring 1.5V across the glow plug, then it is drawing all the current it will draw at 1.5V. There is no such thing a limiting the current without changing the voltage. Bob
  11. BobK

    LED tail lights.

    This is a very bad idea. Bob
  12. BobK

    lights synchronized with music

    Look up active filter and Sallen and Key. As long as you are using opamps, you can make much sharper filters than what you have shown here. Bob
  13. BobK

    amplify ultrasound signal

    I would worry that you might be harming the dog's ears. If it can produce 105db at 20 feet, think what happens when the dog is 2 feet away. You have about 135db now. In fact, it might even be harmful to human ears at that level. There is no way the commerical product you describes is even...
  14. BobK

    RAIL GUN capacitor size/power questions???

    That rings a bell! Bob
  15. BobK

    Need Advice RE Diode for Battery

    Why would you want polarity protection if you are not replacing the batteries on a regular basis? Just make sure they are correct when you install them. A diode would drop some voltage (about 0.6 for a silicon diode, 0.3 for a Schottky diode) so this is a significant drop from a 2.4V...
  16. BobK

    LED tail lights.

    Do a search, this exact issue was discussed on this board recently. Bob
  17. BobK

    amplify ultrasound signal

    Intensity and SPL are the same. I am reasonable certain that the units for $50 are not putting out anything like 105db at 20ft. Where did you get this number? Bob
  18. BobK

    Basic transistor Guitar Amp

    The base is always about 0.7V above the emitter. If the emitter is tied to ground, this is difficult to control. Using an emitter resistor allows you to calculate the bias point much more easily, provides negative feedback to keep it in range, and prevents bad things from happening if the...
  19. BobK

    DC to AC converter

    Or use a '555 timer in the astable confguration and put the output through a capacitor. It won't be a sine wave, but it will be AC. Bob
  20. BobK

    where would I buy a 300 amp 1.5 volt transformer

    Small wonder, since it IS the same guy. Bob
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