tachometer using 555 IC and LM3917

More than strong enough. I started with a gutter drain to 4" pipe transition - that was something to take the rectangular profile of the downspout on a rain gutter to a round 4" pipe. The theory was that the electronics would go in the rectangular portion and the display in the round part.

In practice, I had too much water-proofing varnish over the wires and couldn't bend them enough to make it fit (there's 25 wires)

I ended up using a 45 degree elbow for 4" pipe instead. I had some trouble getting the ring of pipe that the display rests on down in there and cut it on a bias so it would compress enough. The display board is 4mm black anodized aluminum with holes for each led. I put epoxy in the back to seal and hold the LEDs against vibration.

There's a "temporary" 4 inch plug in one end of the 45 (temporary for plumbers only - designed to keep debris out of partially finished plumbing - very thin plastic)

For the display end I found a surplus dome shaped cover of thick poly carbonate. RTV silicone rubber holds it together and seals out the water.

First winter to come along and I had condensate on the inside of the dome. Pried it apart and put it in a warm oven to bake out the moisture then put the whole thing into a large metal can with dry desiccant overnight. The next morning I reassembled it with RTV silicone again and there hasn't been any condensate in it for ~ 5 years now.

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today i bought the 7555 and a thick laminated copper wire. with just 10 turns it start working.when i wound more number of turns(25 as per elekor) it producing high voltage.so by trial and error

**default i need some help in PCB.can i mail to ur ID pls

Sure: ganeth at mail dot com

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That should have been: ganeth at movemail dot com

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Amazing the results when you follow directions...