Wireless nichrome wire heater

Discussion in 'The Projects Forum' started by tleast, Feb 22, 2015.

  1. tleast

    Thread Starter New Member

    Feb 22, 2015
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    0
    I am trying to build a circuit which will close a switch allowing current to flow through nichrome wire upon receiving an rf signal. The application is to burn flash paper, but do so from the other side of the room (aka magic show). The components I am using:

    Adafruit Simple RF M4 Receiver - 315MHz Momentary Type - https://www.adafruit.com/products/1096
    NTE11 NPN SI high current amp (as relay) - http://www.nteinc.com/specs/10to99/pdf/nte11.pdf
    Typical 9V battery
    Nichrome wire

    The receiver has 3 nodes of importance: Vin, gnd, and D2 (or the output for the receiver when the proper rf signal is transmitted. The voltage output of D2 to ground is also 9v, however the current is limited to 200mA). Vin is connected to the positive bus, gnd is on the negative/ground bus. I am then connecting D2 to the base of the bjt, the collector to the positive bus, and the emitter to the nicrhome wire, with the other end of the wire on the negative bus. In theory the wire should heat up when I send the signal, however my bjt is the only part of the circuit heating up, and it rises to probably 200°F+.

    Any thoughts or help would be appreciated!

    Circuit.PNG
     
  2. #12

    Expert

    Nov 30, 2010
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    Not enough giddy-up on the base.
    I'll go think of a different arrangement.
     
  3. #12

    Expert

    Nov 30, 2010
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    The 86 ohm resistor is an educated guess. It's a, "just in case".
    Just in case the 9 volt supply is good and strong, this will stop the lower transistor from melting.
    I guess you are using a 9V battery and a quick pulse. You might get away with no resistor at all and you might find out that a PP3 battery is useless because it can't produce enough power.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I would look at a Mosfet and switch in the drain side.
    Max.
     
  5. #12

    Expert

    Nov 30, 2010
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    Always with the 2N7000, eh Max? :p

    No telling what voltage is being delivered, but I can bet the current is low.
    It's time to measure the voltage at D2 without the transistor connected.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2n7 too small this time!;)
    Max.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @tleast
    Use a shorter piece of nichrome (1 or 2 ohms) Coil the nichrome wire, it doesn't change the resistance but it concentrates the heat into a smaller volume and it will get red-hot in a hurry. Wrap the nichrom around something really small (like micro-screwdriver). Slide it off, bend that coil into a gentile horseshoe. Make sure no loops of the coil touch each other. Then use several 9 volt batteries in series. That small area will get really hot. Enough to combust one small section of paper - then it all goes.

    Anything less takes a whole to heat and you cannt time your flash.
     
    Last edited: Feb 22, 2015
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The CMOS output from the RX can only source a couple of mA at ~3.5V. You will need either a logic-gate NFET or a Darlington...
     
  9. RichardO

    Well-Known Member

    May 4, 2013
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    Consider an igniter for a model rocket?
     
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