.1μF
December 10, 2006
How can a place called Radio Shack not even have .1μF polarized caps?
I need five to build this MAX232 circuit because the level shifters from Spark Fun don’t work for some reason.
Bah. This is absurd.
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I had actually intended on suggesting that MAX level shifter chip back when you brought up the idea, but I had no time… this is what icis did for her parallax RFID kit to turn it into a portable reader, it should work.
Radio Shack stinks for parts these days, which is lame because there’s a great many parts of the country that have no other option. Even here in the valley they’re our main option (along with Fry’s) for Sundays, when all the real nice parts stores are closed.
I think icis raided my parts drawers for her caps…
I had purchased those shifters from Spark Fun, and they… seemed to not do what they say (shift TTL to RS232 levels).
After getting home, I remembered that my PIC dev board has a MAX232 on it, so I looked at how they did it. Turns out that they did it using parts that I do have, so I just breadboarded that up. It works!
Now I’m going to build a soldered-together stripboard version so that it won’t fall apart if I accidentally tug on it while sniffing things in the car.
Oh, and the Processing-based sniffer that partially wrote for me (he did the parts I didn’t know how to start, which was basically the whole framework) seems to work, it’ll just need some polishing after the sniffer is done.
Oh, also, there are *no* other parts places around here beyond RS. If I hadn’t found that other implementation there would have been a many-day wait from Mouser. :(
Seriously, I have no idea what I’d do without my halted. Jameco is somewhat local, but far enough away and only open during normal bus. hours mon-fri, so they’re a pain… fry’s is a wee bit better than RS, but you have to deal with it being a huge computer/consumer elec. store while you’re getting your parts. RS is horrible, thought they do, for some reason, often still have Cinch-Jones jacks/sockets, which is handy if you need to interface, say, a minimoog to the rest of the world.
.1µF
Are you using the MAX232A variant? The classic MAX232[N/C/etc] prefers 1.0µF.
Regardless, the type of capacitor, polarization and exact capacitance appear not to be super-critical per
this unauthoritative Usenet thread. Other discussion indicates that capacitance over 2.2µF can sometimes interfere with proper operation of the charge pump.
Rat Shack’s website claims they carry polarized tantalum 1.0µF caps, probably subject to regional availability. And of course they should have several types of non-polarized .1µF. (You may already have those on hand in the form of ceramic decoupling caps.)