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General : REVISED TIMER PLUS RELAY

Message 1 of 7 in Discussion

From:

UseableTvengineer (Original Message)

Sent: 8/2/2007 1:52 PM

There are a couple of errors with your revised timer +relay schematic that has been posted in the projects album.......the 555 is driving an npn transistor directly with no base resistor present and the transistor is shown driving the relay but connected the wrong way round-emitter and collector reversed and there is no diode connected across the relay coil to protect the switching transistorwhen the relay is turned off.

ive attatched a revised drawing which edge triggers the 555.............

TIMERRELAY.pdf

First Previous 2-7 of 7 Next Last

Message 2 of 7 in Discussion

From:

UseableTvengineer

Sent: 8/4/2007 2:50 PM

heres an even better version with a fixed resistor in series with the adjustable resistor.........

TIMERRELAY2.pdf

Message 3 of 7 in Discussion

From:

sirkituk

Sent: 8/5/2007 5:08 PM

Thanks Craig

I find the input circuit interesting

I imagine it would accept a wide range of input pulses, positive going and of more than about 1volt

Regards

Message 4 of 7 in Discussion

From:

-Whostolemymonkey-

Sent: 8/5/2007 6:25 PM

thanks for the feedback, I've just checked the schematic and yes the npn has been drawn back to front, oversight on my part when drawing the diagram with my cad program.

There should also be a diode across the relay, this was in the test setup I made but again overlooked in the diagram.

Looks like its back to the drawing board for a new diagram, I'll have to edit it and repost it.