Ultra low power consumption

Recently I bought a new door bell. Unlike my old one, the bell is powered by just pressing the button - no batteries!! I guess you only need power for a few milliseconds. In the past I have seen CW transmitters powered by just pressing the Morse key. Some years ago Michael Rainey in the USA made a CW TX that was powered by shouting in to a loudspeaker.

Do you know of others?

Cellphone power harvesting

Southgate News reports on a cellphone design that uses power harvesting to minimise power consumption. I suspect this is a "proof of concept" project rather than a practical design. Clearly, it requires a major name to introduce power harvesting to minimise power usage. Most cellphones use milliwatts or even watts of power on TX.

See http://southgatearc.org/news/2017/july/battery-free-cellphone.htm#.WWT3UrpFxMs

Energy harvesting wireless bus bell push

The latest edition of Land Mobile Magazine (a magazine for professionals in the mobile radio business) has an interesting column showing how London Eco-Routemaster buses are being fitted with a novel sort of bell push (the kind you push to ask the bus driver to stop) which harvests energy from the action of pushing the bell to send a wireless signal through the bus to the driver. The bell push uses an energy harvesting chip from EnOcean a company that specialises in such devices.

The EnOcean evaluation kit (for professional developers) as shown on their website

This is the first time that I've seen a very practical use for energy harvesting. I assume that the device "harvests" kinetic energy (from the pushing action) and thermal energy (from the finger tips) but it must generate a few uWatts for this to work.  So, no batteries, no wires, wireless comms and good for 300k presses. There has to be a QRP application!

For more on this read the article on line at Land Mobile magazine. 

Micropower generation/power harvesting

Linear Technology lists the LTC3108, an Ultralow Voltage Step-Up Converter and Power Manager than runs with an input of just 20mV producing a 5V output to power things such as low power wireless devices and processors. Surely there must be an application for such a device in ultra-QRP portable equipment? Imagine, where can you find 20-500mV of noise from? 50Hz crud in the ground, a thermo electric sensor, solar cells etc. I wonder who will be the first person to make a QRPp uW beacon powered using the 50/60Hz buzz available between a couple of earth electrodes in the ground?