Hi, FWIW despite what Krumlink says there, 555s should be more than adequate for just flashing lights on and off... (though I'm a bit confused, are you talking about in
model trains, yes??). But you wouldn't want to use them for anything that needs
really accurate timing.
In case there was any problem with the appnote Eric recommended, I think where I got the circuit for getting 50% duty cycle from the 555 (which is what you're after!) last year must have been
http://www.williamson-labs.com/555-tutorial.htm
because I remember using the diode like that. NOTE: despite what that page says, using plain old breadboard and stripboard shouldn't be a problem unless you're doing something
fancy, like maybe up in the MHz range or thereabouts. Or if you're using ultra-small capacitors? At 1Hz, it should be completely irrelevant
Anyway, the diode approach worked well enough for me, wherever I got it.
There was also this page,
**broken link removed**
which has absolutely
tons of circuits, and various calculators too for different contexts. It does have at least one 50% duty cycle circuit, though I don't think I used his ones myself. Also ISTR this is the feller who does a lot of model-railway oriented circuits. So you may find some of that (incl. his other pages) useful for future projects.
BTW if it's not obvious: if these lights are drawing a
lot of current, you shouldn't make the 555 drive them directly. 200mA is the stated maximum which should be plenty for many models but it depends what you're using, and near that current you might get overheating problems in the chip perhaps.