12 V External Power and Serial Viewer

You are correct, if you’re using the USB jack to power a v1.0 or v1.1 Mayfly using a 12v source, then there’s no way to interface the Mayfly with a PC for programming or viewing serial output.  However, all Mayfly boards include an FTDI jack that allows you to connect a variety of FTDI cables or adapters in order to communicate with the board in the event of a broken or otherwise occupied USB jack.

Check out this post I wrote last year describing how to connect a small board called the Adafruit CP2104 Friend to a Mayfly:  https://www.envirodiy.org/topic/pc-and-mac-unable-to-communicate-with-mayfly-ver-0-5b/#post-16736

Be sure to scroll down to the bottom of that thread to see the photo I posted showing how you’ll need to solder some right-angle header pins to the end of the Adafruit board in order to plug it into the Mayfly.  Adafruit has since updated and renamed the board the CP2102 Friend but it can be used the same way.

If you don’t want to have to solder something, then you can purchase the older FTDI Friend model that is shipped with long double-ended male pins to let you connect it to the Mayfly with no soldering required.  I wrote about it here:  https://www.envirodiy.org/topic/com-ports-not-connecting-to-logger/#post-15418

The older FTDI model uses a different chip than what is used on the newer Mayfly boards, so you might have to install some drivers if you use that one, I mention this in that post along with a photo of the correct way to connect the board to a Mayfly.  You could also use an FTDI cable, though I don’t know if it comes with the long pin headers so you might have to buy those separately.

Another thing to note, there is a CP2102 USB interface chip built into every Mayfly v1.0 or v1.1.  That’s what allows you to communicate with a PC via the USB jack.  If you connect a separate computer interface board via the FTDI jack, like any of the boards mentioned above, it’s a good idea to disable the Mayfly’s onboard CP2102 chip to avoid hardware conflicts and errors when uploading a sketch.  The small brown block next to the Mayfly’s power switch contains 2 small dip switches.  Here’s a description of them from the Hardware Details page:

Power LEDs and DIP switches:  LEDs indicate board power (green) and USB power (orange).  Useful for easily seeing if the board is on and if USB power is connected.  Green LED will be lit anytime the board has power and the power switch is in the ON position.  Orange LED will be lit anytime power is being supplied through the USB or FTDI connectors.  If Mayfly board is deployed in a sleeping logger station, it is recommended to set both DIP switches to the OFF position in order to save battery power.  Use a small pointed object to gently slide the small white squares of the DIP switch either to the ON or OFF positions.

So if you’re powering your Mayfly with the USB jack, you’ll be wasting a lot of power keeping the LEDs on and also powering the onboard USB converter chip.  I would recommend turning both switches to OFF during your deployment, but you’ll need to remember to turn the USB switch back on if you ever want to reprogram the Mayfly via it’s onboard USB jack in the future.  Here’s something I wrote on the technical discussion thread last year:

The dipswitches are mainly there to let people know their board is working during initial testing or desktop deployments.  Anytime a board is deployed in the field as a “sleeping” station, power savings are important during the sleep period.  So I put the dipswitches on the new versions of the Mayfly to allow people to deactivated the LEDs.  The dipswitch for the green LED only cuts power to the green LED and nothing else, but it will save you about 2 mA.  The orange LED is only on if power is being supplied through the USB jack, like when connected to a computer or when powering from the USB jack like what that converter will do.  Whenever the USB jack is powered and the USB dipswitch is on, the LED is on plus the USB converter chip, which draws some not-insignificant power, so turning off the USB dipswitch will save power and prevent the USB converter from being on constantly.  However, you’ll just have to remember to turn that dipswitch on again in the future if you ever decide to reprogram that Mayfly or want to connect to the Serial Monitor to see some output.

The Mayfly 1.1 is great for powering options – but it does mean understanding the tradeoffs.

For an FTDI cable,  for debug monitoring of the Mayfly this is what I do – https://github.com/neilh10/ModularSensors/wiki/Test-Equipment-FTDI-cable

I also cut some pins to make it a “monitoring cable” that won’t cause a reset when the FTDI USB is plugged in to the monitoring computer. But only do that when you follow how the download works.

When programming the Mayfly I always use the USBC cable, and insure I disconnect the FTDI monitoring cable – as technically they are doing the same job and may fight (electrically speaking)

I would think  +12V could also be provided to the Mayfly 1.1 Solar2 socket.  All possible options – but only if you follow how the circuits work. Using Solar2 would allow the USB-c to be used with the terminal.

I use the board with a solar panel, and so it always has a LiPo 4.4Ahr battery plugged in. On the test bench with LiPo I don’t always need the external power, unless the battery needs charging. 🙂

If you’re using an external FTDI or CP2102 interface board to program your Mayfly via the Mayfly’s FTDI socket, then the Mayfly dipswitch labeled USB should be turned off before connecting the external interface to the Mayfly, and it should stay off the entire time.

What version of the Arduino IDE are you using?  From your screenshot, it looks like you might be using one of the newer versions.  On our software instructions page here:  https://www.envirodiy.org/mayfly/software/    we recommend that you use the Legacy v1.8.x version since there are some quirks about the newer v2.0 and web-based Arduino IDE’s that can cause issues with the Mayfly.

When you plug your CP2102 Friend into your computer’s USB port, what does Windows Device Manager say?  Does a “Silicon Labs CP210x USB to UART Bridge (COMx)” show up under the “Ports (COM & LPT)” list, or is it shown under an Unknown Device tab with a yellow triangle?