Make Sigfox works with potatoes, an ultra low power story

Sigfox Connect yearly event is the opportunity for the company to present its vision on IoT technology evolution. As part of the 2019 edition, the company has introduced Ultra-Low-Power Sigfox communication. In this domain, we are talking about micro-watt to send a radio message over the air the Sigfox network will be able to capture on the fly. You can find a lot of different use-cases for a such communication system. Industrial environment sounds to be the primary market but it can also be included in final products. The main interest of ultra-low-power is to not needing battery but harvesting its energy from many sources, up to the existing WiFi network energy captured from the air.

Energy standpoint

The prototype shown at Sigfox Connect demonstrates a working communication over hundreds of meters indoor, running around 2V with a current of 100uA for about 1 second. This is Micro-Watts radio communication with a radiated power about -20dBm.

Basically, it something you can run on different power sources like potatoes or lemons.

Based on the small today experience, I really recommend to deploy in production potatoes, even if the generated current is lower, the process to put them in production is more easy as lemons are generated lot of juice and complexity in Cu and Mg plates installation.

More seriously, this shown how small can be the energy source to transmit with a such technology. Electromagnetic’s fields like the one created by a WiFi network around can source energy for a such device. What you need is just to accumulate it along time in a small capacity like 100uF before transmission… not so big isn’t it ?

How that device works ?

The device demoed on the Connect floor is a quite clean prototype you can see on the left. It has a really small MCU on the bottom-left corner. This is a PIC-10 device, something like a $0.30 8 bit MCU with less than a Kb of flash and some bytes of RAM.

Basically, this MCU is just piloting a transistor to execute an ON/OFF sequence on a modulated 868MHz signal generated by a SAW (Surface Acoustic Resonator) – the big square in the bottom-middle. A such signal generator is simply like 100ppm quartz, to give you an idea. The frequency can be manipulate a bit based on the way it is powered. The device can only transmit, no bi-directional communications.

This is basically an OOK (On-Off Keying) modulation this device is generating. The message transmitted is a Sigfox standard frame. Regarding the MCU size, for this demo, the transmitted frame is always the same one, there is no more data transported than the identity of the device emitting. This is enough for many use-cases. The frame transmission rate is 800 ms, sounds like 100b/s as usual with Sigfox.

The Sigfox frame is Manchester encoded to avoid long Off period and desynchronization of the receiver. As usual with Sigfox, this device is generating an ultra-narrow-band signal. It can scale and thank to all of this the decoding on the Sigfox base-station is also simplified.

As you can imagine, as the modulation is not a Sigfox standard modulation, it is not today working on Sigfox network. That said, to make the Sigfox network able to proceed a such modulation it is simply a question of software upgrade. That’s the strength of Software Defined Radio: being able to extend the supported modulation. Some base-station have already been deployed in Toulouse for outdoor test and even with micro-watt transmission. So, it technically works ! not only on a Sigfox booth at Connect.

Coverage

A such message can, over the air achieve, some hundreds of meters in-door. The record of 2km distance has already been made in Toulouse. Based on this you can imagine many applications like in industrial domain. The coverage is good enough for industry building, open fields like for storage or parking. It means you can use it in a non dense network with a few base-stations in the expected area.

A standard base-station like a Sigfox micro-base-station will be good enough to support this kind of modulation after a firmware upgrade.

Time to market

As usual on Connect, Sigfox is showing direction and vision, then market will make this technology a product …or not. It works on today Sigfox environment and the prototype is showing the technology availability. Lower the BOM price is, higher the industrialization effort costs, this is where the solution will cost and make time to deploy.

So, basically, the time to market for a such technology will rely on industrial project and interest on ultra-low-power, no battery, work forever solution.

What can you get from a potato ?

As much as I’ve seen, the potato energy was large enough to transmis a message on every 2 seconds in condition you connect 2 potatoes in series to get the minimum voltage. If you have large budget, you can get to 3. It sounds to work like this all along the day, until someone will get them all to make a truffade for sure.

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