Suitability of mDot for MVP deployment


(Heath Raftery) #1

I’ve read lots of people at all stages of development with the mDot as a Node, but precious little about people actually getting them into the field.

I’ve successfully used the Microchip DM164139 Mote to get some small installations off the ground, but am looking elsewhere because of its poor power supply (inefficient, small operating range).

How does the mDot stack up against the following criteria, to get up to a hundred nodes into the field operating through TTN?

  • Is the LoRaWAN stack buggy or feature complete?
  • Is there support for the AU regional parameters?
  • Is deep sleep effective for extremely low current draw?
  • Is it easy to wake from sleep periodically?
  • Is the mbed learning curve steep or can most of it be stripped out?
  • Is the dev environment, including programmer and IDE, cheap, simple and stable?
  • Is it easy to sample a couple of analog channels, including battery voltage?
  • Is it easy to commission individual units with unique ids and shared keys?
  • Is it easy to interface to a battery supply?
  • Is it easy to mount the board in a custom enclosure and attach an antenna?
  • Is radio performance satisfactory?

It’s often so hard to evaluate hardware platforms without spending months butting up against all their imperfections. Hoping I can lean on the community and avoid too many dead ends, and give back where I can.


#2

https://www.thethingsnetwork.org/labs/story/getting-started-with-the-multitech-mdot

?? off course … if the enclosure is CUSTOM for this board :sunglasses:

maybe its more usefull to explain your use case … and then someone here can advise you the right hardware


(Heath Raftery) #3

Thanks @BoRRoZ. Great tutorial, looks very promising. But doesn’t give me much of a real world opinion. I’ve completed thousands of tutorials for hundreds of hardware platforms, only to often find it all comes to a grinding halt as soon as you stray slightly outside the curated walls.

I didn’t want to sound like I was looking for free design services, hence the list of questions instead. But FWIW, the use case is very common - remote sensor measuring a voltage once a day or so and transmitting to TTN in remote Australia. Needs to last a long time without attention and withstand heat from the sun. The crucial criteria is being as off-the-shelf as possible for rapid development and build.

Even though the PCB only appears to have a single screw hole and there’s no mechanical drawing in the datasheet? What’s an easy way to mount that? The custom bit needs to be easy too :wink: Maybe I’m better off buying it populated with headers and soldering to a mounted stripboard… is the pin spacing standard? Is this lack of (or hidden?) fundamental documentation par for the course? That’s the kind of thing that could derail a rapid development project.


#4
  • voltage once a day
  • last long time on battery
  • heat resistant
  • off the shelf
  • ruggedised casing
  • works on TTN australia
  • price ?
  • certified ?

I personally don’t have experience with mdot.
Maybe there are some alternatives to out there but it seems you’ve made your choice


(Heath Raftery) #5

Anyone else have experience with the mDot that could address one or two of my queries? I’m only interested in the queries I made. May have to bite the bullet soon so interested in any heads up.


#6

I’ve had a lot of experience with the Multitech mDot for some early prototypes and a river level sensor that is being widely used. This year I’ve switched to the Multitech xDot for its reduced power consumption and lower cost. A number of these are now in deployed in the field and are working well.

Thanks

Andrew


(Andrew Maggio) #7

Hi @hraftery.

My observation has been:

Is the LoRaWAN stack buggy

Not as far as I can see. Some issues around sleep modes, but they are documented.

or feature complete?

Yes, but my experience had been with LoRaWAN 1.0.1

Is there support for the AU regional parameters?

Yes

Is deep sleep effective for extremely low current draw?

Haven’t tested current draw but am happy with the results I get

Is it easy to wake from sleep periodically?

Yes. Hardware Interrupt or RTC

Is the mbed learning curve steep or can most of it be stripped out?

Pretty easy if you start with their working examples

Is the dev environment, including programmer and IDE,
cheap

Under $100 for the basic programmer. IDE is free.

, simple
Harder than Arduino, simpler than Eclipse

and stable?

I’ve had issues with the online environment, which effectively meant it was down for a few hours.
You can use mBed offline components as well if you prefer

Is it easy to sample a couple of analog channels,

Yes

including battery voltage?

This might be a bit harder, since (I think) analog inputs will be represented as a percentage of battery voltage, so you’ll always read 100%. There might be a constant voltage source on the MCU that can be used. Somebody with more experience than me can probably correct my comments.

Is it easy to commission individual units with unique ids and shared keys?

Yes if you have the same AppEUI and AppKey. (But note potential security issue of sharing keys between devices).

Is it easy to interface to a battery supply?

Yes, see specsheet for details.

Is it easy to mount the board in a custom enclosure and attach an antenna?

Easy enough, if you buy the version without header pins.

Is radio performance satisfactory?

As far as I can tell


#8

Why use a programmer as this module seems to support the mbed USB-drive feature?

Also as this module seems to support the ST-Link interface for debugging and programming one of these thingies should do.

I don’t own an mDot yet so I haven’t verified it myself :relaxed:


(Heath Raftery) #9

The module doesn’t come with the USB port interface, but it’s <$100 to get the adaptor.

Yeah I’m a bit thrown by that. Is the USB interface only for “Flashing” (using the rather novel USB drive copy method)? Do you also need an ST-Link for debugging? What about serial console? Is the full size developer kit necessary?

Reading between the lines from hundreds of different references seems to suggest that the USB interface on the Micro Developer Kit can maybe do Flash (via drive copy), plus debug (via an embedded ST Link driver), plus serial (via a virtual com port), but it’s not at all clear.


#10

The dev kit is the ST-Link programmer for the device, you either plug the mDot into it or use a cable to connect the adaptor to a header on your board. I have previously used the full size UDK for this purpose before moving to the xDot. For this I use the SWDAP boards to program xDots on my boards but this doesn’t support mDot in its firmware.

Andrew