[Shannon Hicks]

For a Meter Hydros 21 sensor, check the manual that came with the sensor to double-check that they haven’t change the wiring colors lately, but the usual pattern is red is data, white is power, and black is ground.  So connect red to D2, white to Vcc, and black to GND.  For that screw terminal board, D2 will get connected to D7 if you plug the grove cable into the D6-7 socket on the Mayfly board.  We usually use the Mayfly’s D7 pin for SDI-12 sensors in all our sample code.

[Shannon Hicks]

Data plan prices are kind of a hard thing to put an exact total on, since it varies depending on various factors the station owner can choose, like cell carrier and transmitting interval, but I can give example costs for our typical configurations and deployments.  For example, most of our stations transmit around 10 parameters every 5 minutes, using Hologram cards on Digi LTE modules.  That results in an approximate usage of 12MB of data per month.  We use the Maker Edition Flexible Data plan from Hologram, which is $0.40 per MB, plus $0.60/month base cost, resulting in around $5.40 per month.  But that’s only for Hologram cards, using LTE modules.  If you use 2G boards, the cost is a few dollars higher per month due to the slightly larger data usage that 2G modules seem to use.  (2G will be sunsetted soon in the US, so we’re upgrading all our stations to 4G LTE).  So essentially the Maker Flexible, pay-as-you-go plan that Hologram offers will result in around $5-8 per month of data usage.  There are other SIM card providers out there that some people are using with Mayfly loggers that I think cost more than that.  We haven’t found anything cheaper or easier to use than Hologram, which is why we recommend them.

[Shannon Hicks]

We typically code our stations to cutoff modem transmissions at 3.45v, and file operations at 3.4v.  The Mayfly will stop operating around 3.35v, so if you set your modem cutoff too low, then you’ll stop transmitting AND stop collecting data on the memory card at the same time.  By setting the modem cutoff a little above the memory card logging cutoff, then you’ll have time to visit the station to swap batteries before you start losing data on the card.  But in general, the station shouldn’t be falling that low repeatedly.  Use a larger solar panel and make sure the battery pack is matched to it, based on the amount of sunlight you get on a typical day.  Most of our stations stay in the 3.7v-4.0v range without user intervention to replace dying batteries.

[Shannon Hicks]

The jumper for selecting whether the I2C grove port is constantly powered or switched powered was not intended to allow the user to turn off I2C devices on that Grove port.  I designed the board that way because I wanted to give users at 2 separate Grove ports that could be powered either continuously or switched, because the other 4 Grove ports only give you the option of 3v-switched or 5v-switched.  To avoid confusion, I probably should have only allowed people to choose switched power on the D4-5 Grove port and made the I2C Grove port be always on, but on earlier versions of the board, I was using a sketch that turned on and off the power to the I2C Grove jack because of a certain peripheral I was using on that jack.   So the jumper is basically a relic from an earlier iteration of the Mayfly that has limited functionality to most people, but it’s there if you need it for a specific reason.  Almost all users will leave it in the default 3.3v constant position.

[Shannon Hicks]

Right, that’s why I’m thinking you just need a screw terminal to Grove board, and since you only need 4 wires, you can use something like this:  https://solarbotics.com/product/29118/

[Shannon Hicks]

All bare-board electronics such as the Digi LTE cellular board and the EnviroDIY Mayfly are sensitive to static electricity and theoretically they could be damaged if you aren’t careful.  That said, the Mayfly is pretty hardy and I haven’t experienced any problems after handling multiple thousands of boards over the last few years in all sorts of environments.  However, the LTE module is more sensitive because of its exposed pins and more-sensitive electronics.  You shouldn’t put it in your pocket or carry it around in your hand while walking around, especially on carpet in low-humidity environments.  But you should be safe to remove it from the package and examine it if you’re careful, and you can connect it to the Mayfly board (using the LTEBee adapter board) at any time.  Just be careful that you don’t damage the small header pins since they are easy to bend, especially when removing the Bee module from the adapter board.

Another thing to note, we usually ship most of the items EnviroDIY makes (like the Mayfly, the LTEBee adapter, and other accessories) inside a foil bag that has a “static sensitive” warning on it.  Those are just the default bags that the manufacturer uses, and isn’t an actual warning.  Just be careful with the boards like you would any sensitive electronic device:  avoid moisture and physical damage.

[Shannon Hicks]

We used to sell the 6-pin screw terminal boards on Amazon, but don’t anymore.  We do offer a 5-pack in our EnviroDIY ship page if you want to buy 5 all at once:  https://www.envirodiy.org/product/envirodiy-grove-6-pin-screw-terminal-adapter-pack-of-5/

Otherwise as Beth said, you might be able to use a regular 4-pin screw terminal board that is widely available from lots of different vendors.  We made the 6-pin version specifically for interfacing with the Campbell Scientific OBS-3+ turbidity sensors that have 6 wires and require 3 ground connections.  It’s easier to use this 6-pin board with those sensors than trying to fit 3 ground wires into one single screw-terminal on regular boards.

Your sensor probably has a power wire, ground, and two data lines (analog or digital).  If you have anything other than that, you might want to double-check before connecting it to the Mayfly.

The link Beth posted above is a 4-position, 3.5mm headphone jack adapter board made by someone else.  We have a 3-position headphone jack in our shop, but you don’t need a headphone jack if your sensor has bare wires on it.  You’d only use a headphone jack if you bought a sensor that comes with a 3.5mm plug on the end of the cable, like what Meter Group does.

[Shannon Hicks]

Yes, Digi-Key has over 4,500 of them in stock right now:  https://www.digikey.com/en/products/detail/digi/XB3-C-A2-UT-001/7932027

Mouser only has ~350 right now and is slightly more expensive than Digi-Key, so that’s why we recommend Digi-Key.

Note that Digi (makers of the cellular modem) and Digi-Key (an electronics distributor) have very similar names, but are completely unrelated.

[Shannon Hicks]

Here’s an update for this topic:  we’ve implemented the online shop here on EnviroDIY to sell 5-packs of various products, including the vertical microSD card adapter board.  All prices include shipping (to US addresses only).  Restocking items on Amazon has been extremely slow lately, so if anyone wants to buy Mayfly boards, kits, or accessories in multiples of 5, please use our EnviroDIY shop instead of Amazon.  You’ll also save 10% that way too.  We will continue to sell on Amazon as well, but this shop allows us to fulfill bulk orders quicker and without emptying our Amazon inventory as frequently.

[Shannon Hicks]

After thinking about this old code yesterday, I was curious about what actually happens if a tip occurs during a long delay period, like the 2-second delay on line 123 and and 2.5-second delay on line 125 (which are delays to give the Xbee 900mhz radio module time to successfully wake up and then finish its routine before sleeping).   I programmed a test board with the sketch from above, but increased the delay time to 10 seconds for each of those lines, to give me enough time to experiment.  What I found was that if a simulated bucket tip on pin D10 happens anytime during a 10-second delay, the delay instantly ends and the interrupt routine successfully gets executed (meaning a tip gets counted) and then the sketch moves on with the next line of code (either line 124 or 126, depending on which delay the tip happened in).  So this shows that no tips will get missed by the Mayfly, but the delay period gets instantly cut short.  If you’ve got a radio or cell module that needs multiple seconds of uninterrupted wait times before doing the next step, then care should be taken about how you handle interrupts from D10 during that time.  You could unattach the D10 interrupt during those important delay times, and then reattach it when you’re done, or find another way to handle either the interrupt or the telemetry delays.

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