[André Sarmento] needed to connect a computer to an RS-485 bus. A simple converter can be sourced online, but the only thing he could find locally that was even close was a USB to RS-232 converter. He used that component to craft his own USB to RS-485 bridge.
RS-485 is often used for remote sensors as it provides a method of connecting electronics over long distances. The converter which he started with seems to be encased in a hot-glue-like substance. A bit of time with a torch and he was able to get to the components on the board. There are two stages, one which converts RS-232 to TTL, and the other converts TTL to USB. [André] removed the RS-232 chip and patched his own board (shown on the left) into its TTL lines. He was also able to add a few more configuration options, like using an external power source, and having a few jumper-selected resistor options.
http://www.aliexpress.com/item/USB-2-0-to-RS485-DB9-COM-Serial-Port-Device-Converter-Adapter-CABLE-1M/627897482.html
At 9.82 USD I am sure that it would have been cheaper to buy one with shipping than to make one.
Whats your time worth? That being said if you have the time and the parts sure nice hack!
Yes, if your time is worth something, spend it waiting a week and a half for a part to arrive from China.
22 days from china, I know, I order a $1, free shipping, buy-it-now item every day.
Anyhow, I wanted to point out an article error, feed to a 7805 must be 7.5V** min to get 5V out.
ofcourse you all know this, I’m sure it was just a typo.
** all numbers in my statement are approximate **
Thanks for the correction.
Post has been updated.
I don’t know your locale, but thrift stores, (places people leave stuff for a tax write-off and the store sells it to someone else to raise money for a charity) often have Nokia USB adapters. Sometimes for as little as a $1.
http://jethomson.wordpress.com/2010/02/21/diy-usb-to-serial-cable-for-3usd/