If what you are looking for is something like www.101science.com/eleclinks.htm
There are many types out there but you may have to order the plans to get the circuit. After having made my own electronic tach using 100 leds and making the board and mounting the whole mess in a nice enclosure I think the price they are asking for <a href="http://www.dkselectronics.com/]this device [/URL]is pretty reasonable. Building electronics and buying one part at a time is expensive and time consuming. You could also try one of those 1001 Electronic plans books, thats where I got my plans from.
Good luck, happy soldering!