Serial Port Prototypes

Has anyone made a serial port interface? I would like to build a rpm meter using a serial port of my laptop. The schematic should be easy but I can not find any information on it. Any ideas? Thanks, Brian

Goodhart10 years ago
Here is the Tutorial for the RS232 serial port interface

It doesn't sound like it would be overly complicated using an FET and of course a DAC. This (link) looks like a bit much though...

But, just in case: Here are the data sheets & etc.

And one last link for the night: A patent has been issued for a similar device that may give you some ideas....

gmoon Goodhart10 years ago
Let me elaborate on Goodhart's comment:

Possibly because it's obvious to most hardware guys, he neglected to mention that most modern microcontrollers have serial protocols built-in (two of the 4 links above use Atmel controllers.) So AVRs or PICs are great platforms for starting this type of project.

You generally need a rs-232 'glue' chip (MAX232 project) to convert the uC voltage to normal serial.

Some more modern serial ports can deal with 5 volts, however. I've used the E-Lab EDE702 LCD driver, which is based on a PIC. It uses a 33K current-limiting resistor to drop the rs232 voltage. Worked fine for me, so a similar approach might work...
Goodhart gmoon10 years ago
Thank you.