Add on serial port - parts questions

I have a boarduino which has no serial port. I do not wish to buy a usb converter cable when the circuit for the serial port on the arduino is so simple.

I have a qustion on some of the parts and substitutions. For instance - the resistors and caps I can take care of - but I am unsure if i can substite a general NPN for the 547 and PNP for the 557 the schematic calls for.

Also - how important is it to use high speed diodes like the 1N4148 - would regular diodes work for protection?

Yes, you can substitute. As best I recall, I used a 3904 and 3906 when I built my serial Arduino. Note these cases are backwards from the BC parts.

Don't know about diodes, as I had the specified parts on hand for that.


I found Radioshack carries the correct diodes and the transistors you mentioned. Hopefully I'll be loading a new program on it this weekend!!!


I have parts in hand and want to get started - however the site that seems to host the schematics has been offline since friday so I haven't been able to begin. Anyone have either the serial or single sided serial schematics they could send me? C J A N Z O W (AT) Q R S 1 (DOT) (COM)

Nevermind - its online today and I’ve saved it.

Might you post a link to the site?