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  1. hevans1944

    LM317 question.

    I am not trying to blow their horn, but while visiting my son here in Atlanta GA he produced a dozen or so back issues of Elektor magazine for me to peruse. One of these (June 2013) has an article that may offer a possible solution to your power supply build: re-purpose a PC ATX power supply by...
  2. hevans1944

    replicating gun recoil

    Why won't that work? Assuming you first remove the anchor rope (or chain)? Not that I think this is a viable row-boat propulsion method. Maybe better to erect a small sail and blow on it? After all, if you can tack against the wind, surely you can provide your own wind!:D
  3. hevans1944

    LM317 question.

    I think you are right about the purpose of the diode in the 7812 circuit. Problem is, the forward bias is current-dependent for both the diode and the base-emitter junction of the 2N3055. The forward bias voltage of both junctions is also temperature dependent, so unless the two junctions are...
  4. hevans1944

    LM317 question.

    Minus the diode connected to the base of the 2N3055, and the use of the fixed-output 7812 instead of the adjustable LM317, this circuit is the same as the first circuit you uploaded. As I stated earlier, I am not a big fan of using emitter-followers without feedback to "boost" current output...
  5. hevans1944

    replicating gun recoil

    Sorry about that, Chris. You are right and I was wrong. Primary recoil starts as soon as the bullet begins to move down the barrel, not when it leaves the barrel. The net momentum of the bullet is the product mv, where v is the muzzle velocity and m is the bullet mass. This is conserved by...
  6. hevans1944

    help designing simple 4022 circuit

    If you look at the forward voltage versus forward current transfer function of a silicon, or germanium or Schottky diode you will see that both the forward voltage and the forward current go through zero simultaneously, and that the forward voltage drop is a function of the current through the...
  7. hevans1944

    Grid Tie Inverter MOSFET Replacement part IRFP25N50N

    Well, it is what it is, and what you removed from the inverter. It could be a bad inverter design, but we don't have a schematic to see what is going on. Read the information at the website link provided by @GPG to get an idea of what is going on, but realize the "schematics" are conceptional...
  8. hevans1944

    Grid Tie Inverter MOSFET Replacement part IRFP25N50N

    It's a power MOSFET rated 200 V at 30A. Might be imported from Thailand. Found the datasheet here.
  9. hevans1944

    major stress of railway track

    No need to modify the track to apply strain gauges, but watch out for oncoming trains. It is important to clean the area where the gauge will be bonded to the sides of the track and attach the gauges with cyanoacyrlate adhesive (superglue). After soldering very small solid jumper wires from the...
  10. hevans1944

    replicating gun recoil

    Recoil mainly occurs only after the projectile and expanding muzzle gases exit the barrel. neglecting the small amount of gas ported to operate the bolt after firing. This is the only time a transfer of momentum can occur. The time interval from cartridge ignition to bullet leaving the barrel is...
  11. hevans1944

    LM317 question.

    An emitter follower is not the most efficient way to boost current. Try this circuit: This was copied from edaboard.com forum and I have not built or tested it. It appears to have been copied from the application notes on the National Semiconductor datasheet, attached. You should read the...
  12. hevans1944

    help designing simple 4022 circuit

    Zener cathode connects to output. Zener anode connects to ground.
  13. hevans1944

    help designing simple 4022 circuit

    Years ago, when I was just starting my formal education in electrical engineering, a co-worker demonstrated to me that Maxwell's Equations applied to everything electrical and electronic... current flow in wires, electrons in vacuum tubes, current carriers in semiconductors, you name it. The...
  14. hevans1944

    LM317 question.

    This time I remembered to use the calculator! 10 mA = 0.010 A. Square that and you get 0.0001. Multiply by 120 Ω and you get 0.012 watts or 12 mW (not 12 μW!). Still, that's considerably less than 250 mW or 1/4 W. On resistor power dissipation: you can connect two resistors (of the same power...
  15. hevans1944

    Don't Fence Me Out

    Please don't try to power your electric fence with a high-voltage, low-current transformer! This may work using a small neon-sign transformer, but it is very dangerous. Fence chargers produce a pulsed output whereas the transformer output is continuous. So instead, use a commercial fence charger...
  16. hevans1944

    IR Switch Trigger in Specific Setup

    A passive infra-red (PIR) motion sensor driving a timer to set the "ON" time after it is triggered should work. You might even be able to buy one off the shelf. The tricky part is setting the sensitivity and the field of view so passers by who don't stop to view the art won't trigger the light...
  17. hevans1944

    help designing simple 4022 circuit

    Damn. I knew I should have used a calculator for this! Good catch, @dorke. The OP is going to use +15 VDC for Vcc, so plenty of head-room available for the LM317, but 10 mA still exceeds the 4022 maximum source/sink spec of ±1.5 mA. Oh, well, it may still work since we don't really care if...
  18. hevans1944

    help designing simple 4022 circuit

    @guskenny83 your circuits are substantially different from the one you show in post #3. However, I consulted with my son, who is also an electrical engineer, and he said that your circuit will work if high-efficiency LEDs are used. That is, even at low currents, the LEDs should still be visibly...
  19. hevans1944

    Merry Christmas and a happy new year ...

    I've said it before, but I will say it again: Happy Holidays and Best Wishes for a FANTASTIC New Year. And thank you, Adam, for remembering Kris and Donna. And of course a HUGE thank you to Ian for making this forum happen. Hop
  20. hevans1944

    help designing simple 4022 circuit

    The 4022 counter/decoder is a CMOS device with very limited output current capability. It should not be used to directly drive an LED. The resistance of the potentiometer in your first circuit is in series with the LED and if of sufficiently high value to limit the current through it to 1.5 mA...
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