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continuity tester on Stamp? — Parallax Forums

continuity tester on Stamp?

MatthewMatthew Posts: 200
edited 2005-04-09 14:05 in General Discussion
Hello. I'm planning on using a Stamp controlled transistor to send current to an electrical match. The match blows at about 0.5 amps. Is there anyway I could have the Stamp make sure the e-match is still intact?

Thanks,
Matthew

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-04 04:31
    Matthew,

    ·· Sure!· One simple way is to (assuming you're using an NPN transistor) connect a stamp I/O pin to the collector, and use a pulldown resistor of around 10K (You may have to adjust this).· When the stamp I/O pin reads high, the e-match is still intact.· Of course, you will have to test it while it's not active (Between turning it on).

    ·· This is similar to how my headlight circuit worked on my computer car (RIP).· This assumes the e-match is connected directly to the collector and the other end to positive voltage.· Once the e-match is blown, you'll read low all the time.



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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • MatthewMatthew Posts: 200
    edited 2005-04-04 04:52
    Chris, thanks for the very quick reply, however I'm not entirely sure if I'm visualizing this correctly.

    I'm seeing ground and a 10k resistor being connected the collector, with the resistor going to an I/O pin. Am I wrong or right?

    Thanks,
    Matthew
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-04 05:05
    Matthew,

    ·· No, I have to make some assumptions here due to lack of details about transistor type, voltage, etc.· Assuming a 2N3904 (Just within tolerance of the current) and a 5V high voltage:

    ·· The Stamp pin for control would go through a 220 Ohm to 1K resistor into the base of the transistor.· That's one connection.· The transistor's Emitter will go to ground.· That's the second connection.· Now, from the collector you are presumably going into this e-match, and the other lead of the e-match to 5V.

    ·· From the collector you will also have another line going to an second pin on the Stamp (INPUT) and also tied to ground.· It doesn't matter if the pull-down resistor is at the Stamp pin or the Transistor's collector.· Electrically it's the same.· But the resistor goes to ground from there.

    ·· This keeps the Stamp's INPUT pin from floating when the e-match is blown.· You should only see a HIGH on the INPUT pin when the OUTPUT pin is LOW, and the e-match is good.· Otherwise you will see a LOW.· If you see a LOW, and the OUTPUT is LOW, your e-match is burnt, toast, history, the blue smoke has come out...· tongue.gif

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-04-04 05:19
    Okay,

    ·· I was thinking about what I said, and I built my original test circuit.· The only thing I had to change, which I remembered afterward was the pull-down resistor.· I switched from 10K to 100K due to minimal current draw across my load, which, being a bulb wasn't wanted.· IOW, a 100K resistor will also work, and may be a better solution for you.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • nick bernardnick bernard Posts: 329
    edited 2005-04-05 21:05
    where do you get your electrical matches from? are you developing an automated pyrotechnic display?
    http://focus.ti.com/lit/ds/slis010a/slis010a.pdf
    try a TPIC6595N in your circuit to maximize your number of outputs

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    " Hey! Why is there silicone on my hemostats?"

    Post Edited (nick bernard) : 4/5/2005 9:11:24 PM GMT
  • dandreaedandreae Posts: 1,375
    edited 2005-04-05 21:14
    Nick,

    Check the model rocketry sites and you'll find them.· I typed in "Electrical Matches" on Google and found all kinds of information mostly related to model rocketry.· They even show you how to make them on one of the sites.

    Dave



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    Dave Andreae

    Tech Support
    dandreae@parallax.com
    www.parallax.com

    ·
  • MatthewMatthew Posts: 200
    edited 2005-04-09 14:05
    Nick, I got them from PerformanceRocketry.com
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