An inexpensive way to interface to potentiometer

[hamster]

Here's how to read a pot, using only two resistors and a capacitor:

 

http://hamsterworks.co.nz/mediawiki/index.php/Cheap_Analogue_Input

 

It is based around the technique used for the joystick interface on the Apple II.

 

Only downside is that you need to calibrate the the limits - but perfect as a paddle interface for a game of Pong, where you could just remember the max & min readings.

[johnbeetem]

Cute!

 

I've done this using a 555 timer, which I notice is how The Woz did it (in his case with a 558 quad timer).  I think you get better stability with a 555 rather than depending on the FPGA's input threshold voltage.  You can get a low-voltage 555 these days, or use a 74VHC123A dual one-shot.

 

If you really want to avoid external chips, you might get better results with a precision FPGA input standard that uses a Vref pin or use differential inputs comparing to a common Vref.