Instructables

what diodes do i need?

i made a litle schematic (picture is in paint) as an extra for my binary clock, since the wart is a litle bit to handy (i can reverse polarity) and i dont want to destroy my precious attiny2313, so i thought of of some diodes and made a plan. but, i had 4 zenerdiodes lying around, and i tried it, but nothing happened, the clock didnt power on. i think the diodes are to heavy, so i was wondering which ones i needed. its all in the scheme and i think its pretty obvious (i made it in paint, so the quality isnt good, as wel as my english :P)

Picture of what diodes do i need?
Re-design4 years ago
Get a small full wave rect. from Radio Shack. Connect the pos to the pos of your clock and the neg to neg. Put that inside you clock case. Attach the power socket, that you wall wart plugs into, to the a/c connections. That way no mater which way the polarity is set you get the right polarity to the clock. You can even plug in an a/c wall wart (of the correct voltage) and you still get the correct dc to the clock. This is very similar to what is used as a protection circuit in expensive electronics that have external power sources. Good luck.
seandogue4 years ago
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godofal (author)  seandogue4 years ago
i want something that makes it possible to put in the power at any way, and still have it working, your scheme just blocks it... but i didnt know its being used already :P i never thought of that, just liked this idea... and i dont get the part that says zeners arent good, they let the power trough one way, and dont die when theyr getting overpowered the wrong way, thats all i know about them and the difference from normal diodes that do die if overpowered... and what are schotky diodes? how are they different from general purpose and zeners?
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godofal (author)  seandogue4 years ago
that dropping the volts isnt that bad (right?) becouse i run it with an attiny wich (if i remember correct) runs from 3.7V to 5.XV (not sure on that X, but at least more than 5.3V) so it shouldnt matter if im correct. oops, just read that it would be ~3.3V, but then again, i could just made the wart 6V, and then its good right? but i read in a beginners elektronics book that zeners will short when overcharged, but repair themselves (or something like that) what makes it usable after overcharging, and normal diodes keep dead. and about the volt regulator, i need 7.5V for it to function (drop it to 5V) and then it isnt enough anymore right? and if i place the diodes before the regulator, i need to give it about 10V, wich would get alot for a clock...
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godofal (author)  seandogue4 years ago
nice scheme, how do you make them? il look if i can order some diodes/ wave rectifier and a V reg. and do i need a heatsink for that?
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godofal (author)  seandogue4 years ago
i have no idea how much current it draws... i really need some better equipement :P
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godofal (author)  seandogue4 years ago
i got a multimeter, but i ment an Oscope, good iron, a good lab elecktricity thingie (no idea what its in english) one of those that you can use for protoboards, with adjustable voltage and ampere meter... but all that is really to expensive :P
Look at Velleman.be for their scope/meter/signal analyser - great value.
godofal (author)  godofal4 years ago
btw, still have the question of what software u use for the schemes
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godofal (author)  seandogue4 years ago
first timed it on 1 minute, wich took alot of time... then did the math, reprogrammed it (line 65 ticks) and timed it again, 1 second to slow (but i manually timed it, so thats not realy accurate at 1sec) so i timed it for 12 hours, what made it 26 minutes to slow. then i redid the math and redid the programming, and now it runs good (i think, gotta test it for 24hours, and if that turns out ok, im going to test it for a week, and see how accurate it is :)
jeff-o4 years ago
Use a 1n4001 diode. It is rated for 50V and 1.0A. That should be plenty for this application. They are pretty easy to find. However, you must be aware that there will be a 1.4V voltage drop at the output (standard for a bridge rectifier setup like this), so if you feed in 4.5V you'll only get about 3.1V. Don't forget a filter capacitor (47uF-100uF) across the output, too. Come to think of it, insufficient voltage may be the reason the clock didn't power on in the first place...
frollard4 years ago
What you're thinking of is a bridge rectifier.

http://commons.wikimedia.org/wiki/File:4_diodes_bridge_rectifier.jpg

The diodes themselves have to be rated for the voltage and amperage you're working with - as with capacitors, a safety margin of 1.5-2x bigger than you need should be a safe bet. Look for diodes with a low voltage drop.

You can also get bridge rectifiers sold as a single unit.
your diagram is basically the same, just drawn a little differently.
godofal (author)  frollard4 years ago
k, i saw that diagram a couple of times, but i never associated (no idea if thats right) it with mine, didnt really look at it anyway :P but i see that it works the same way.