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I'm using the following two rf433 modules in combination with two Arduino Unos.

After testing them both at 5V (in combination with the RadioHead library), which worked, I decided to test the improvement in the range, while powering the transmitter with 12V (I'm using an external power supply). This answer suggested that a NPN transistor can be used to provide enough voltage for a logic HIGH (I tried connecting everything as depicted on that picture). I used a RFP30N06LE MOSFET and wired everything as depicted in the picture below:

this

After a minute or so, I noticed that two wires started to melt, so I quickly disconnected everything. One wire is the orange one, connecting the drain of the MOSFET with the DATA pin of the transmitter, the other one is the ground wire from the source of the MOSFET to the GND. I also noticed that the MOSFET got quite hot.

Can someone explain what I'm doing wrong? Thank you.

**EDIT:**As @Andy aka suggested, the data pin doesn't need level shifting. Upon removing the MOSFET and both resistors from the circuit the transmitter is now working at 12V. The grounds of the external power supply, the transmitter and the Uno have to be tied together.

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closed as unclear what you're asking by Michael Karas, Olin Lathrop, Enric Blanco, PeterJ, Dmitry Grigoryev Jun 6 '17 at 9:53

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ A circuit diagram is more useful than a wiring diagram. As it stands, I'd have to look up that transistor and see if you have connected it properly. Not much inclined to do that this afternoon. \$\endgroup\$ – JRE Jun 5 '17 at 10:18
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    \$\begingroup\$ VTC until you can come back with a real schematic. \$\endgroup\$ – Michael Karas Jun 5 '17 at 10:21
  • \$\begingroup\$ The first thing I saw was that cartoon where apparently a schematic should be. Not gonna read the text now. Downvoting for throwing a joke at us instead of a schematic, and voting to close since without reading I don't know what is being asked. Screw this. \$\endgroup\$ – Olin Lathrop Jun 5 '17 at 10:41
  • \$\begingroup\$ I apologise. I am not an EE by profession, so this was the best/easiest/quickest way to show you how I have everything set up. \$\endgroup\$ – RunoTheDog Jun 5 '17 at 10:44
  • \$\begingroup\$ Fritzing can also produce schematic diagrams. Coax one out of it to get this question cleared up, then learn to use a better program (KiCAD or the free version of Eagle) to make your schematics inthe future. \$\endgroup\$ – JRE Jun 5 '17 at 10:59
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The answer you refer to is one that I gave and I gave it with reference to a different device namely the TX433. You are using an FS1000A and it doesn't need to have the data line shifted - it will work with a 5 volt digital level: -

enter image description here

There is little to guarantee that the circuit is 100% correct but Ii do believe the input circuit (for the data) is accurate.

But, your problem is this: -

Will the FS1000A run from a 12 volt supply?

There isn't too much hard evidence that it will. If you can find a reasonable data sheet, it might tell you. Some people appear to suggest that it will but no hard evidence and no data sheet make this a non-preferred device in my book.

Of course you could have made a mistake when wiring it up. Those fritzing cartoons are meant to take away the pain for beginners but they also stop them thinking what they might be doing.

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  • \$\begingroup\$ Thank you for answering, Andy. I will remove the MOSFET and try supplying 5V to the data pin (while running the other two at 12V). I will also add the pull-down, as suggested by Glenn. \$\endgroup\$ – RunoTheDog Jun 5 '17 at 10:38
  • \$\begingroup\$ "running the other two at 12V"? What might that mean? \$\endgroup\$ – Andy aka Jun 5 '17 at 10:43
  • \$\begingroup\$ The VCC and GND pins, of the transmitter, will still be powered from the external (12V) power supply. I thought this was what you meant, when you said, that the data pin, doesn't have to be level shifted? \$\endgroup\$ – RunoTheDog Jun 5 '17 at 10:46
  • \$\begingroup\$ The GND pin runs at 0 volts not 12 volts. \$\endgroup\$ – Andy aka Jun 5 '17 at 10:50
  • \$\begingroup\$ Right, but it's tied to the GND of the 12V vcc. Right? \$\endgroup\$ – RunoTheDog Jun 5 '17 at 10:51
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It sounds like you may have reversed the supply connection to your proto board. I don't know if this is possible but getting the data line to melt would require something as extraordinary as that. Or is it possible that the data line is pulled high internally and only requires a ground to key it? The datasheets I found seem to be lacking in details.

In any case the resistor in series with the gate is not required. You may however wish to tie the gate to ground with a ~5-10k resistor to ensure full turn off.

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  • \$\begingroup\$ Thank you Glenn. The supply connections are most definitely not reversed. I will try supplying 5V to the data pin (while keeping the other two at 12V, as suggested by Andy). I will also add a pulldown, like you suggested. \$\endgroup\$ – RunoTheDog Jun 5 '17 at 10:41

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