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  1. hevans1944

    Creating a Velocity Measurement Tool

    If you connect the string to a velocity transducer (try a small permanent-magnet DC motor for starters), you can tell when the rep begins (and ends) by looking at the velocity profile. With a DC motor you could use an analog comparator to trigger data acquisition when a certain (low) velocity...
  2. hevans1944

    Creating a Velocity Measurement Tool

    I visited the TendoSports web site and looked at some the videos posted there. It seems to me that the primary thing their sensor measures is velocity, not displacement. Displacement is fairly easy to derive from velocity by integration. A suitable velocity sensor can be as simple as a homopolar...
  3. hevans1944

    Dual controlling of a Relay

    I implemented a functionally similar circuit about fifteen years ago to control a number of electrically controlled vacuum valves. I used DPDT ON-OFF-ON toggle switches. One pole provided switch position information to an Allen-Bradley programmable logic controller. The other pole was hardwired...
  4. hevans1944

    ring oscillator with stable frequency

    Is this circuit just part of the clock generator for a much larger digital integrated circuit design? Can you use an external resonator to set the frequency? BTW, what frequency are you trying to obtain? Relying on analog techniques to establish a clock frequency for a digital IC doesn't sound...
  5. hevans1944

    Reduce Physical Size of Old Chopper Circuit

    After looking at your photos and the partial schematic, I have to ask myself, "If it's not broken, why try to fix it?" This controller may be old, but as you said it is a "proven, robust design." I doubt you are going to improve on the IG-BJT chopper with more "modern" components that would...
  6. hevans1944

    About Radio Transmitters

    Would you please post a link to where it states "under FCC law, unlicensed transmitters can only transmit with a range of 200 ft. or less". There is only one band (26 to 27 Mhz) where unlicensed, un-certificated, kit-based RC transmitters are permitted, and then only on six particular...
  7. hevans1944

    Noob Question About Current From Voltage Regulators

    Yeah, I guess I showed my age on that one. I don't remember when usage changed from E to V for representing potential difference, but apparently it has. So I will try to remember this "new" convention in subsequent posts. It is always a good idea when writing equations to explicitly define each...
  8. hevans1944

    Noob Question About Current From Voltage Regulators

    It might help if you could show us how you "do calibration references." Just because your power supply can provide 2A doesn't mean it has to! OTOH, if you need a "calibrated" current source in the range of 100 pA to 1000 mA with a compliance voltage between zero and 1 VDC, a variable voltage...
  9. hevans1944

    Noob Question About Current From Voltage Regulators

    Only thing that matters is you have an adjustable voltage power supply capable of providing (up to) 2 A to whatever load resistor you connect to it. The current the power supply provides to the load is I = E/R where E is the voltage in volts, R is the resistance in ohms, and I is the current in...
  10. hevans1944

    Help Selecting A Switch (Novice)

    Adam, AC8NS is my call sign. Look me up on QRZ.com. 73 translates to "best wishes" and de is French for "from".
  11. hevans1944

    Using an APD/Photon Counter

    @davenn : an avalanche photo diode, or APD, is a quantum-mechanical photon detector typically constructed as a PIN junction device operated with reverse bias. At low reverse bias voltages it behaves as a simple photo diode with reverse current proportional to light intensity. At a critical...
  12. hevans1944

    Help Selecting A Switch (Novice)

    Near as I can tell, any M2044 series switch from NKK should work. Differences in part numbers appear to be related to terminal type and switch body mounting styles. Use Kris' wiring diagram. That is, 12 V applied to two positions at each pole. Can't tell if you did that with the NKK toggle (my...
  13. hevans1944

    Using an APD/Photon Counter

    You would be well-advised to purchase the Hamamatsu MPPC Module C11205-350 which contains the biasing and charge amplifier circuitry you need, operating from a ±5 V DC supply.
  14. hevans1944

    Help Selecting A Switch (Novice)

    What you are asking for can be achieved with a special double-pole triple-throw (DP3T) miniature toggle switch, Model M2044B2B3W01-VA from NKK switches, available from Digi-Key here. Other manufacturers also make this specialty three-position toggle switch. The contact switching arrangement is...
  15. hevans1944

    How long would it take the capacitor in the given circuit to completely discharge?

    I provided you with this link in reply to a similar question you asked in another post. Clearly, you either did not follow the link or did not understand the content therein, for you replied not, either to thank me for my "answer" or indicate you have any understanding of the subject matter...
  16. hevans1944

    How long would it take the capacitor in the given circuit to completely discharge?

    Answer this question first: How long did it take the capacitor in the given circuit to completely charge if the switch was in position 1?
  17. hevans1944

    12 volt positive ground need help with 7905 circuit

    This is a tough problem to solve with a linear voltage regulator because of the large (10 A) current required combined with the need to drop about 14 - 6 = 8 V across an external pass transistor to boost the current capability of the LM7905. The transistor will dissipate about 80 W under these...
  18. hevans1944

    what percentage of current remains in the resistor?

    The current in the resistor has dropped to about 37% of the initial charging current after one time-constant of time has elapsed. The relevant equation is Ir = (Vsource / R) (e^(-t/RC)) where Vsource is the voltage applied to the RC circuit, R is the resistance in ohms, C is the capacitance in...
  19. hevans1944

    Concept: High Voltage Power Supply

    Well, the main idea is to have fun and learn something. That looks like a safe enough sized coil to start with. If you want to learn a bit more about how Tesla coils work, here is a PDF file that explains it without overwhelming you with math. It takes a very hands-on approach to how one 2nd...
  20. hevans1944

    Concept: High Voltage Power Supply

    Those are typical components for a voltage multiplier. Diodes with 15 to 20 kV ratings would be preferred. These are made by soldering a stack of 1 kV chips together and packaging the stack as a single high-voltage diode. Forward voltage drop is about 0.6 V per diode in the stack, sixteen diodes...
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