R.G. Is This Your Latch Relay Idea...Pic Link

[Incubus]

I saw what you were saying about modifying Trans' latch relay cct.

I drew this up.....I think it's what you meant.

http://img188.exs.cx/img188/9076/latchrelay0016ze.jpg

[R.G.]

Not exactly. I'll draw it up.

[Transmogrifox]

www.geocities.com/transmogrifox/latchrelay0016ze.jpg

I think that's more in line with what RG was thinking.  I imagine RG will do a nicer diagram that isn't as crude as my cut-paste-copy-move job in MS Paint.

Notice, this mechanical switch epitomizes what the ideal CMOS inverter output would look like.  Thus you may reduce the 4.7 uF cap down to 2.2uF, and perhaps experiment with less--just to see what gives you dependable operation with minimum capacitance.

"Why?", you may ask:  This will decrease the drain on your battery due to switching.  If you're taking in more charge than what is necessary to latch the relay, then you blow that energy away as waste when the capacitor discharges.

[R.G.]

That's it.

IMHO, there's one component left off. It's a reservoir cap across the 9V at the switch, and connected by a single wire to the negative end of the relay coil capacitor. That keeps the pulse current inside a tight loop at the switching circuit and does not let it get out into the rest of the circuit. The switch circuit itself could be pop free, but the ground current could induce a pop when it's triggered.

[Incubus]

I've redrawn it again with the things you've both said.....I think this is what you meant ?

http://img41.echo.cx/img41/6042/latchrelaycorrected2pe.jpg

Fell free to add this also Trans as it's easier to have it on your site.

[Incubus]

Le Bump.

[R.G.]

Yes, mostly.

I'd feel better if you would erase all those ground symbols and instead run wires to the bottom of the 22uF cap at the switch. Then one one wire to a remote ground symbol. That's really more like it should be wired for minimum power/ground transients.