TTL 3,3V to RS232 Level converter – part 1

I’m building an RS232 interface module for the Fonera router. Now, there are three ways of doing that: using a MAX232 chip, a DS275 or with transistors (source) . Lots of people recommend the first solution on forums and bulletin boards. It would be more reliable then the other two.

The MAX232CPE is a very common component, and can be found pretty easy at your electronics reseller. But that chip needs a supply of 5V. The Fonera however supplies only 3,3V. The MAX3222CPN (low voltage brother of the MAX232CPE) is capable of interfacing the TTL serial port of the router, but the chip is a lot harder to find. On the Internet everything is possible, ofcourse, DigiKey has these chips available, but shipping costs for only two chips double the price. So I ordered two samples of the MAX3222CPN+ chips from Maxim yesterday, the MAX3222CPN seems to have been replaced by this ‘+’ variant by the manufacturer. We’ll see whether they send me the samples, and if they don’t, I’ll stick with the transistors instead.

MAX3222-MAX3241 Datasheet

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