I'm trying to identify this port and read data off it. It's 1cm across, including a small square on the lower left. 3 pins, leftmost near square seems to be GND and rightmost reads 3.3V+ w. respect to leftmost pin.

It's an unlabelled port on an unbranded watt meter, I haven't found any markings or writing when opening the case, there's no manual/specs, and I'd rather not disassemble the internals in hopes of finding out.

I'm assuming I can interface with this with an Arduino, but I don't know where to start. Any identifications or tips on how to communicate with it will be appreciated.

Attached pics: 3-pin 3.3V port Watt meter

  • \$\begingroup\$ Let me google: Simple DC Power Analyzer Watt Ampere Meter 12V 24V Solar Wind Analyzer Power US$6 es.aliexpress.com/item/… \$\endgroup\$
    – tlfong01
    Commented Mar 21, 2022 at 3:28
  • 1
    \$\begingroup\$ @tlfong01 where on that page is there info about what the 3pin port is? I'm not trying to identify the meter, I'm trying to figure out what the 3pin port is and how to read from it. Either you're seeing something that's not showing up on my end, or you misread the post. \$\endgroup\$ Commented Mar 21, 2022 at 4:06
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    \$\begingroup\$ @Darling_1kkg Perhaps RS-485? If so, either MEWTOCOL by Panasonic (possible) or acting as a MODBUS RTU (Remote Terminal Unit.) The latter is free to use in a product, so more likely that? I read that MEWTOCOL is a possibility but have never used it. I'd set things up using a fancy logic analyzer with protocol identifying algorithms to help out just to be sure. But perhaps it's 3.3 V RS-485, electrically. See this pinout, perhaps? It's possible what you see as 3.3 V is the (+) wire. \$\endgroup\$
    – jonk
    Commented Mar 21, 2022 at 5:13
  • \$\begingroup\$ Simple Arduino Home Energy Meter - DIY Life the-diy-life.com/simple-arduino-home-energy-meter \$\endgroup\$
    – tlfong01
    Commented Mar 21, 2022 at 5:20
  • \$\begingroup\$ There's really nothing much there to 'identify'. It's just 3 generic gold plated pins on a 0.1" pitch which could be used for pretty much any imaginable purpose. Ask the manufacturer of the device. \$\endgroup\$
    – brhans
    Commented Mar 21, 2022 at 12:09

2 Answers 2


Other identical watt meters boast that it's an auxiliary power input port, with a third pin for resetting the measurements.

So it's not a serial port to begin with.

  • 2
    \$\begingroup\$ Please state a reason for the downvote - I will not link to shady websites selling these products and anyone can verify from identical products that it is an auxiliary power connector as many websites include the 3-pin connector for it or as an additional item that can be purchased. \$\endgroup\$
    – Justme
    Commented Mar 21, 2022 at 7:44
  • \$\begingroup\$ idk why this was downvoted, out of all the suggestions this seems the most likely by far. Would upvote if I had the rep for it. \$\endgroup\$ Commented Mar 21, 2022 at 11:43

The most common use of a 3 pin uC is the serial EPROM port programming port.

This is for factory use only.


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