Ibutton Protection Circuit (OneWire)

[andybarrett1]

Thank you for reading this…..

I a wondering about protection for the PIC port if I am using a Dallas iButton device. I have seen circuits using a 33R resistor in series and a FR107 Fast recover diode across the probe. And another up to the supply rail.

My question is why the use (specific) of a fast recovery diode… Will a ordinary or even a Schottky diode be the same …..Is there a reason ?

Sorry if posted in wrong place.

[Charlie]

Anything is better than nothing - it's to protect from fast transients like lightning striking some distance away or ESD.
There's a continuum here. Some energy source / device sensitivity combinations will do no damage with no diode at all, some combinations will leave a smoking hole where your circuit used to be. Faster protection is better, but the difference in protection from fast recovery vs. Schottky is pretty small. I use Schottky and have never seen a failure (touch wood). If the lead to the device is fairly short - say under a couple meters, you will be safer yet. YMMV.

[andybarrett1]

Thank you

I guessed the any protection is better than nothing.....

Now I guess I just need keep my operators away from man made fibres !

Don't want smoking holes !

BR
Andy

[Acetronics2]

Hi, Andy

may be it's a good idea ...

as iButton devices are generally hand held by everyone ( understand people ignoring what is ESD ! ), the diodes inside the Pic may be somewhat weak ...

so, a couple of fast diodes and a small series resistor are to consider.

don't forget to read Maxim AN244 ... http://www.maximintegrated.com/app-notes/index.mvp/id/244

Alain