To save the troubles of zero crossing detection just use a opto-coupler
with zero-crossing detection built in. Toshiba make some that are
surprisingly cheap.
The one I have used is a TLP3063 (this is more or less an industry standard
number).
It will directly fire a TRIAC.
If you don't need to turn on for less than one half cycle then this is the
easy way.
You could then easily run your project off a battery as the opto-coupler
only needs about 5mA.

This has turned out to be a long interesting thread...

Cheers
        Dennis

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FROST - Electronic Design, Manufacture & Consulting.
Dennis Frost
Tel:   +27 331 965125
Cel:   +83 2275216
Email: dennis.frost@pixie.co.za
Pietermaritzburg, South Africa
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