Author Topic: Protecting PIC inputs connected to DS18B20  (Read 5206 times)

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Offline txescientist

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Protecting PIC inputs connected to DS18B20
« on: January 18, 2013, 10:55:05 am »
I am building USB temperature data logger wtih PIC 18F4550 and DS18B20 (3 wire mode). My question is how to protect PIC input from voltage spikes induced in long wire (during storm, etc..)?  Found one solution: http://www.maximintegrated.com/images/appnotes/214/1189Fig02a.gif Using two more FETs for RX and adding MOVs should be enough to save PIC. Any help is appreciated.

Thanks in advance,
Milos, applied physics student.
 

Offline notsob

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Re: Protecting PIC inputs connected to DS18B20
« Reply #1 on: January 18, 2013, 11:44:03 am »
I've seen these used to protect input line on USB chips

http://www.semtech.com/circuit-protection/emi-filters/stf203/
 

Offline ptricks

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Re: Protecting PIC inputs connected to DS18B20
« Reply #2 on: January 18, 2013, 01:19:16 pm »
tvs diode will work or a 1k resistor in series with a zener diode going to ground will work too.

 

Offline txescientist

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Re: Protecting PIC inputs connected to DS18B20
« Reply #3 on: January 19, 2013, 04:34:05 pm »
Than you all for responses.

Just fund right solution: DS9503

http://datasheets.maximintegrated.com/en/ds/DS9503.pdf

All the best, Milos.
 

Offline tld

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Re: Protecting PIC inputs connected to DS18B20
« Reply #4 on: January 20, 2013, 07:26:49 pm »
Just fund right solution: DS9503

That certainly looks like *a* right solution, but I'm not sure it's *the* right solution (singular... only right solution).

You'll probably be fine with it, so you don't really need to read the rest of this post, I just felt like dumping some random thoughts, for archive, google and whatnot. ;)

While that solution is probably fine, I'm thinking it's major selling-points include board space etc.  If you're just mucking up some quick thing on a prototype PCB, you'd probably do just fine with "normal" ESD protection using random jellybean parts.  Instead of an integrated package, you could grab a 5.1V zener and a couple of resistors for example.  That'd give you basically the same thing it seems.

Biggest selling point for "fancy TVS-things on small chips" seems to be that they're low-capacitance devices etc, solving problem you'll have on higher speed links.  With the speeds of 1-wire networks, you often don't need that, and could just as easily build something yourself, as use a tiny custom package.  Oh, and note that the package you mentioned seem to be for 2-wire operation, not 3-wire, so remember to add something for the power-rail.

What I did the last time I wired up 1-wire for outdoors use (10 meters or so, so not exactly long-range), was something like this:

Power:
Power-rail - 5.1V zener (to ground) - fuse (in case of shorts on outdoor wire) - 6.8V TVS diode (to ground) - outdoor cable - DS18B20

MCU - 5.1V zener to ground - 6.8V TVS diode (to ground) - outdoor cable - DS18B20

Ground - outdoor cable - DS18B20

And I mean literally *something like*, I don't recall exactly, but something like that...

There's off course also caps on the power rail, which would further limit rate of voltage rise, I sprinkled on some resistors as well.

The thing has been alive since last fall, and yes, there has been lightning storms.  Sample set of one though, so not exactly a statistically valid sample-set, nor scientifically tested. ;)

Disclaimer: I am *not* an EE, more of a programmer on an adventure into electronics.  Reliability (including ESD) is just an itch I'm trying to learn to scratch properly. ;)  Another goal on my adventure is to try to form good habits, and it seems to make more sense to make a habit to think of things like ESD, and deal with it properly wherever needed, than being dependent on custom ESD protection for every unique case...

Anyways, just wanted to do a quick brain-dump just in case it could be interesting.  I'm hoping others will correct me if need be.

tld
 

Offline txescientist

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Re: Protecting PIC inputs connected to DS18B20
« Reply #5 on: January 20, 2013, 10:19:17 pm »
http://pond1.gladstonefamily.net/surge-protection.html
http://itech.fgcu.edu/faculty/zalewski/CDA4170/files/1wire.pdf

It is great to hear what other people did on real projects and how it is worked out...
Must agree, zener and TVS are more robust solution than a single chip - there is a no board size issue.

As yours, my cable will be max 15 meters.

Thanks for reply.

 


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