Friday, April 30, 2010

RS-232 to TTL level shifter

While working on equipping Pokey with a bluetooth modem (articles forthcoming), I found that I needed an RS-232 to TTL level shifter, so I could safely hook up the modem to the PC for troubleshooting.  I probably should've saved the time and bought one from Sparkfun Electronics.  But, it was fun to build.  Here's how.

A re-purposed computer mouse cable with PS/2 connector plus a DB9 adapter provided the connectivity to the computer on one end and the bluetooth modem on the other. Some web searching uncovered a few suitable circuits.  I selected the SparkFun diagram (pdf), which I drew up in Eagle, then laid out a board to fit into one of the small enclosures I got from the TGIMBOEJ awhile back (a Hammond 1551KBK). Here are the Eagle files for the project.

SparkFun Circuit Diagram in Eagle

POV-Ray Rendering With Eagle3D

Fabricating the PCB went easier this time than in prior projects. I used single-sided board this time and the transfer went really well too.  Instead of using just the sponge, I soaked the board in pure ferric chloride for about a half hour then scrubbed with a sponge (and no water this time!). The copper came off lickety split. Took about 2 or 3 hours from inception to completed device. Not bad!

The etched and drilled level shifter PCB

The populated circuit board, enclosed, and wired

Completed RS-232/TTL Level Shifter

I'll admit that the circuit didn't work the first time I tried it, but a little bit of troubleshooting and rewiring had it working perfectly in no time!  What's nice is that I can now use this for all kinds of serial communications projects and it is dandy for troubleshooting communications.

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