1 Volt Keyers
	Version 1
	I have build many electronic keyers before. I'm also interested in QRP which is most often battery operated.
	Having that background I wanted to test how low one can go with keyers power supply voltage, or,
	how many battery cells would be needed.
	Standard CMOS Integrated circuits work down to 3V supply voltage but I wanted to go lower than that,  to 1.5V.
	The only way to reach 1.5V supply was to use discrete semiconductors. MOSFET's were out because
	they start conducting with 3V gate voltage. J- and N-FETS also need about 1.5V opposite voltage to be biased.
	So what have we left, the old bipolar transistors and silicon diodes, which have threshold voltage of  0.5-0.7V.
	That is less than half of 1.5V, which leaves some playroom for circuits.
	I ended up to schematics which is very similar to the early days electronic keyers. The keyer works even with
	0.7V supply voltage. With 1.5V current consumption is only 0.5mA, when the side tone oscillator is off.
	This keyer has dot priority meaning that dots are produced when both paddle contacts are on.
	Speed is adjusted with potentiometer X2 and weight with X1. As weight is a question of taste,
	operator needs to adjust it only once. Therefore X1 can be a trim pot.
	The side tone oscillator is optional. Its power consumption depends mainly on the loudspeaker
	impedance. My speaker is from telephone handset (landline) and is 55 ohms. Another model was 200 ohms.
	with 55ohms speaker average current is about 7mA
	One AA battery serves as power supply in this equipment. 1000mAh capacity is good for 83 days continuous use,
	without sidetone. Another source says, that AA capacity is 2750mAh, which would mean 230 days.
	My construction is Manhattan style as I always do.
	Pekka OH1TV
	23.7.2008
					last update
	Schematics v1  1.5V  0.5mA				6.8.2008
	Pictures
	Version 2
	After I had done the 1V keyer I was curious to see, how low the current consumption could be done.
	I used the same schematics but changed component values. My aim was first to decrease current to 1/10 of the original
	version, to go to 50 uA current with 1.5V battery. I left the sidetone oscillator out as it would take far too much current.
	As current decreases, transistors get slower. In this application it is just a good thing. RF sensitivity decreases.
	As modeling gave good results I built one. And yes, it worked fine. Max keying current to transmitter is more than 1mA.
	One AA battery( 1000mAh) will last for 2.3 years. I used one AAA battery, which has about half of AA's capacity.
	Schematics v2   1.5V  50uA
	Version3
	Next natural step is to go to 1/100 current of version 1. I got still good results with modeling.
	Power consumption is 1.5V  6uA, or 10uW. One AA battery (1000mAh) would last in theory for 19 years !
	In the model keyer worked down to 0.7V voltage. Maximum keying current is only 100uA which is quite low.
	My ICOM 756 has the same 100uA keying current.
	I have not build this one but I believe it would work. Impedance levels in the paddle wires are high and there might be
	RF shielding challenges. On the other hand, transistors are very slow with these currents.
	Schematics v3   1.5V  6uA
	Version 4
	Version  4 goes one decade down again in collector currents. We are 1/1000th of the original.
	In the model it works with 1.5V battery but not with 0.9V any more. I think we have come to the limit.
	One AA battery lifetime would be 190 years…
	There is another reason why this is not practical: Max keying current is only 10uA.
	We do not get the signal out any more, hi!
	I have not tested this version in practice.
	Schematics v4   1.5V  0.6uA
	This was a real fun project.
	Pekka OH1TV
	8.8.2008
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