JeeLabs

Freevolt's "RF Energy Harvesting Whitepaper" figure 1 shows the energy harvested from RF as .1µW/cm² to 2000µW/cm², but the text gives energy densities .01µW/cm² to 100µW/cm². This density estimate may be per transmitter(?) so the harvesting estimates only make sense if you assume multiple transmitters each contributing to the total harvested energy.

In Figure 3 they have a chart which shows ~30µW harvested from an unspecified, un-sized "Patch array 1x2" antenna".

Your optimistic estimate is 16µW/cm², so it is in the range of their power harvesting claims. (though I doubt their unspecified antenna is 100cm²)

What is feasible with an energy budget of 30µW? Well, using off the shelf microcontrollers and RF modules, you can send a packet every two minutes using the least optimistic estimates from http://jeelabs.org/2013/09/08/3-years-on-one-set-of-batteries/ . The power consumption of the radio is the biggest element of the power budget, so you can add sensors without hurting your power budget too much. And probably you can do better than this with a better transmitter than the old RFM12B.

I don't think their claims are impossible for sensors that operate in the µW range of average power consumption, though though the top end estimate of 2mW/cm² in table 1 seems way too optimistic. But as you point out even a task as simple as blinking an LED a few times a minute is pushing it. You'll never power a mobile phone this way.

The whitepaper is…

> JeeLib is an Arduino IDE library for JeeNodes (made by JeeLabs)

Source code: https://github.com/jeelabs/jeelib

Website: https://jeelabs.org/202x/sw/jeelib/

The latter redirects to a page that shows Git commits, but it's a hidden page in a Dutch site about online casinos. It does look a bit shady. In the GitHub org of jeelabs, there are only two authors and neither seem to be based in the Netherlands.

Here's an archived website that documents the jeelib library.

https://archive.ph/nmF5Q

Relevant line:

> a Sleepy class for ultra low-power sleeping of ATmega and ATtiny µC’s

From a quick skimming of the codebase, I couldn't find this class. If I were the author, I would have forked the Sleepy class for my own use.

Edit: Here's the definition of the Sleepy class.

https://github.com/jeelabs/jeelib/blob/6df2d8da785aca77790e94121de7908e85179530/Ports.h#L345

It uses avr-libc's sleep functions.

> <avr/sleep.h>: Power Management and Sleep Modes

https://www.nongnu.org/avr-libc/user-manual/group__avr__sleep.html

I try to find a better way to try this and after reading hackaday on Forth 2017 which highlight the latest (2017) update on Forth development:

https://hackaday.com/tag/forth/ (mainly this: https://hackaday.com/2017/08/04/take-the-blue-pill-and-go-forth/#more-267209 )

I find this and you can run the whole thing on my MacBook in 5 minutes. It is great:

https://jeelabs.org/article/1720b/

In general the mbed has the better options for low power , but if you prefer the arduino, this would be a good starting point:

http://jeelabs.org/tag/lowpower/

And if you want a long-range, low-power wireless connection - use LoRa , There's a driver here:

http://www.airspayce.com/mikem/arduino/RadioHead/classRH__RF95.html#aa9184ab8aec1c3c54a275d08c7e85c66