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  1. CDRIVE

    Model engineer needs help

    The LM358 output will not swing up to the 5V rail. Because of this the PNP will not turn off when pin 7 is high. You will need at least 2 Diodes in series with the PNP's base to compensate for this. Why not eliminate the PNP altogether and drive the shunted node directly through a Diode...
  2. CDRIVE

    Model engineer needs help

    One caveat on my last post... I think a pull-up resistor on pin 2 would be a good idea. The trigger pin is sensitive and it's floating when the OpAmp output is high. Chris
  3. CDRIVE

    Model engineer needs help

    Clever!! I like this! It eliminates the two transistors (Q1, Q2) in my design while producing the same logic. Chris
  4. CDRIVE

    Model engineer needs help

    Yes, the output is taken off pin 3. Check your transistor basing. That seems to be the most common cause of circuits that should work ..not. Chris
  5. CDRIVE

    Model engineer needs help

    Based on the above I believe you want this. The 555 triggers Hi immediately when the 358 output goes low but the RC time constant doesn't start timing until the 358 output goes high again. So, however long the 358 stays low the 555 will add 10 sec after the 358 goes Hi again. Chris
  6. CDRIVE

    Model engineer needs help

    Before I answer that please answer a few questions. Referring to your Servo Driver schematic below... I'm assuming that the level low circuit, including the 555 monostable is supposed to control this servo driver 555. Is this correct? If so is it supposed to automate an SW1 closed or open...
  7. CDRIVE

    Model engineer needs help

    That's an off the wall method of triggering a monostable 555? The trigger pin should be starting (triggering) the 10sec high output. All you have to do is reverse the logic of the 358 by swapping the + - inputs. This will provide the low logic trigger that the 555 needs. Do you understand...
  8. CDRIVE

    Model engineer needs help

    Here..
  9. CDRIVE

    Model engineer needs help

    My last post was in response to a post that the OP deleted. I hate that!!! :(
  10. CDRIVE

    Model engineer needs help

    You're illustrating a simple pulse stretcher, which Steve mentioned earlier. A 555 will easily handle this easily but it belies your description, which is a variable. Chris
  11. CDRIVE

    Model engineer needs help

    There in lies my problem. You're describing a "Variable" that's easily handled by uC logic but I don't see a 555 alone dealing with this. In my mind a none uC solution would require clocked logic. Maybe I'm looking at this wrong... Comments? Chris
  12. CDRIVE

    Model engineer needs help

    After re-reading your first post I have a clearer picture of this. Wouldn't 2 sensors (Hi - Lo) be a superior system? On that note a single 8 pin DIP Picaxe could replace the OpAmp and the 555. I'm sure the 08M2 model will operate down to 3V, possibly 1.8V but not sure about this. Chris
  13. CDRIVE

    Model engineer needs help

    So what happens if it's 4sec or 3sec? Also, define immediately. Chris
  14. CDRIVE

    Model engineer needs help

    Stew said 5 & 10 seconds, so I'm thinking. Problem is I'm not thinking so good. I started the weekend early. Chris
  15. CDRIVE

    Beards and Hurricanes

    When the media anoints you Messiah you have only to wave your hands over your subjects and all is well. We are living in an alternate reality. Chris
  16. CDRIVE

    Model engineer needs help

    Glad to see it's going to be used. Anyway, we got sidetracked. Did you answer Steve's question? Chris
  17. CDRIVE

    Magnet coil help (turns, gauge, for coilgun)

    OK, I see I need to clarify my statements regarding steel projectiles. First up is steel bird shot. Yes, the EPA forced it on us and bird hunters hate it. It doesn't have the ballistics of lead shot and manufacturers were forced to try all kinds of shot cup and coating tricks to protect...
  18. CDRIVE

    Magnet coil help (turns, gauge, for coilgun)

    This is a misconception shared by the masses of the uninformed. I suggest you google how armor piercing ammo is made. We DO NOT want hard steel of any kind making contact with our barrels. Chris
  19. CDRIVE

    Model engineer needs help

    Nice pix Stew. Did the engine begin life as raw castings from a supplier? Chris
  20. CDRIVE

    Model engineer needs help

    Yes, you won't find "Ferroequinologist" in the dictionary but if you Google it ... ;) Chris
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