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From: Cursitor Doom <cd@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: Ultra-Low Power Operation
Date: Mon, 07 Oct 2024 00:49:06 +0100
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On Mon, 7 Oct 2024 00:26:01 +0200, Lasse Langwadt <llc@fonz.dk> wrote:

>On 10/6/24 16:35, john larkin wrote:
>> On Sun, 06 Oct 2024 13:28:46 +0100, Cursitor Doom <cd@notformail.com>
>> wrote:
>> 
>>> On Sun, 6 Oct 2024 09:25:47 -0000 (UTC), piglet
>>> <erichpwagner@hotmail.com> wrote:
>>>
>>>> Cursitor Doom <cd@notformail.com> wrote:
>>>>> Gentlemen,
>>>>>
>>>>> I vaguely recall going back the best part of 60 years now, there was a
>>>>> competition among radio designers (AM in those days) to come up with
>>>>> the design which would operate at the lowest possible supply voltage.
>>>>> This had arisen, I would guess, as a result of the 'semiconductor
>>>>> revolution' and all these designers would compete to develop a working
>>>>> radio using ever more absurd Vcc levels. I'm pretty sure someone
>>>>> managed to get something credible together that worked off of just
>>>>> over 1 volt but can't be sure after all these years and there's
>>>>> nothing I could find on the 'net about such a contest, either. But I
>>>>> do remember it, for sure.
>>>>> I'd just be interested to know what can be done with <1V today. Anyone
>>>>> know?
>>>>>
>>>>
>>>> Around that time there were published designs using germanium transistor
>>>> inverter to step up 250-300mV to a few volts for driving more conventional
>>>> items.
>>>>
>>>> Complete radios built from Ge tunnel diodes were done too.
>>>>
>>>> Silicon bipolars are constrained by 0.6/0.7V forward junction voltages but
>>>> once started can continue stepping up from much lower voltages. LT made a
>>>> boost converter IC that once started continued boosting from 100mV.
>>>>
>>>> Depletion fets let you go much lower, Jan Panteltje has posted his 20mV
>>>> booster which lights a LED.
>>>
>>> I take your point, Piglet, but many of us still have Ge devices in our
>>> junk boxes, so need not be constrained by the greater barrier height
>>> of their Si equivalents.
>>> Using some sort of boost converter is not in the spirit of this quest!
>>> The circuits that were being submitted to the design contest were all
>>> designed to operate straight from very low DC supplies, with none of
>>> the shenanigans you mentioned. :)
>>> This might be a tall order, but I'd like to see a circuit for an AM
>>> radio which could be powered from half a volt.
>> 
>> Crystal sets need no power.
>
>I remember an ancient popular mechanics that showed one made a coil a 
>capacitor and an old razorblade and pencil to make a diode

There are quite a lot of such combinations you can use. Safety pins,
lightbulb filaments and copper plated pennies that have been baked for
example.

>> There were some that rectified power from several stations to amplify
>> one.
>> 
>> And yes, a depletion fet or one of the zero-threshold fets could
>> detect and amplify at very low supply voltage.
>> 
>> Where can you buy a half volt battery?
>
>a zinc and a copper nail in a lemon? ;)

Again, lots of ways to make batteries. We found all this fascinating
when we were children, but kids today just don't seem to give a damn
about it.