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  1. BobK

    Magnet coil help (turns, gauge, for coilgun)

    wire diameter 0.0675 in. means you will get 14.7 (call it 15) turns per inch. At 1/2 in diameter, that is 23.5 ft for a single layer 1 inch long. Each layer would be 0.135 in larger than the previous one, so 4 layers will just about use up your 120 ft of wire. Question, why are you...
  2. BobK

    Magnet coil help (turns, gauge, for coilgun)

    Sounds like a good candidate for experimentation. Bob
  3. BobK

    NiCd Battery Charger Schematic

    A NiCad battery changer is more complicated than that. You will destroy the batteries if you just leave it on with no capability to detect that the charge is finished. Go here for lot's of info: http://batteryuniversity.com/learn/article/charging_nickel_based_batteries Bob
  4. BobK

    Can someone confirm the gain here please.

    Returning to your question, to get a gain of two, eliminate the capacitor and two resitors in the circuit connecting the DAC to the + input. Just connect the pin directly to the + pin. Not sure why the capacitor was there, if you want to slow the response to changes, you could place a...
  5. BobK

    Can someone confirm the gain here please.

    Thanks, yep, that would be the one. So you are using the 5-bit DAC, giving you 32 levels between 0 and 5V? Bob
  6. BobK

    Can someone confirm the gain here please.

    Which PIC is that based on? Bob
  7. BobK

    [Need help] Rectangular Area Detection

    Do you mean a specific object, or any object? Bob
  8. BobK

    Question about circuit diagram

    How much current are we talking about? For efficiency a buck converter would be best. bob
  9. BobK

    driving a relay

    BJTs are current driven devices not voltage. You need to calculate how much current goes from the base to the emitter, based on how much current you need in the collector circuit. You don't need a voltage divider, you only need a base resistor that can be calculated as follows. Use your...
  10. BobK

    Can someone confirm the gain here please.

    Justin, I am still trying to figure out how you are getting 0-5V analog out of the PIC12f629? This chip has no DAC or even PWM module. Is it mislabled, and you are actaully using another part? Bob
  11. BobK

    Magnet coil help (turns, gauge, for coilgun)

    Supak, I am not trying to discourage you from experimenting. I think this project could be a great learning experience for you. But as C.C. and I, and others have pointed out, your expectations are far from realistic. Tone it down a bit and try to learn as you go. First, make a single...
  12. BobK

    Heat Pads for Animal Hospital

    Have you considered a microcontroller and PWM? This would solve your regulator problem. Bob
  13. BobK

    Can someone confirm the gain here please.

    Justin, The gain of your opamp circuit is indeed 2, but you have taken the output from the PIC and put it through a voltage divider that halves it, so the output of the op amp is the same as the output from the PIC. Is this a DAC output? I did not know there were any small PICs with a DAC...
  14. BobK

    how to cut off supply?

    That is the very article that got me back into electronics. I had two drill drivers that kept wearing out their batteries with its dumb charger. I didn't want to pay for his PIC though, so I got my own and one plussed his design by using a buck converter controlled by the PIC. This was my...
  15. BobK

    PIC08 Circuit To Control 12v PC Fans

    You could also use a 78L05, which comes in a TO92 case, like a transistor. Bob
  16. BobK

    Vintage stereo receiver re-lamp with LEDs

    Scenario 2 is wrong. The white LEDs are not protected from reverse voltage. Move the 1N4004 to connect between the AC source and the rest of the circuit, so that the current flows to all of the LEDs through the diode. Or, put the two white LEDs in antiparallel and leave the blue + diode as...
  17. BobK

    Can someone confirm the gain here please.

    Except that the input is divided by 2 by R1 and R2, which is why I said 1. Bob
  18. BobK

    Magnet coil help (turns, gauge, for coilgun)

    Well, just 1 second's worth of ammo for supak's gun is 2000 x 3.5g or 7kg or 15.4 lb. Bob
  19. BobK

    Magnet coil help (turns, gauge, for coilgun)

    Just to make it clear what the 880 lb recoil would do, if the gun weighs 32 pounds (1 slug of mass), then an unrestrained gun, after firing for 1 second would reach 880 ft / sec or 600MPH! Bob
  20. BobK

    Can someone confirm the gain here please.

    Negative feedback is what you want, it controls the gain. I think Steve was looking at the wrong op amp (U3B). That one does appear to have positive feedback. What is the function of that op amp supposed to be? Bob
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