Cheap1

Cheap1 is an attempt to build a robot for about $30.00.  It ended up costing a bit more, but not much. Cheap1 uses a 74LS367AN for a buffer between the parallel port and an L293D motor driver. If you hook up four of the parallel port thru hex buffer outputs to the L293D and then use the remaining 2 hex buffers on the chip for input, you can make a pretty reasonable robot.  To get the connection from the parallel port to the prototype board, I used a Modular 8 Wire Adapter Kit from RS (pn 276-1406) and a short piece of 10BaseT cable.  Left the RJ45 connector on one end of the cable and snipped the other end off.  Used the wires to plug into the hex buffer. Go to www.boondog.com to find a three chip 74367 setup (it's in the 'tutorials' link).  I just used one chip to get six lines.  There is a short, but helpful QBASIC program at www.boondog.com that will show you how to access the parallel port on your machine (same link as the tutorial that shows the schematics). Be sure to put a heat sink on the L293D just in case the motor stalls out (it gets hot quick if it does!). The heat sink shown in the picture was made by cutting a TO 220 heat sink in half and super gluing it to the chip. Here's a modified version of the motor controller.

For the drive train, I used a Tamiya toy gear set (available from  www.robotstore.com ) that comes with two 3 vdc motors. The wheels are from an old toy.  Used heat shrink to get them onto the axles. The on board power supply is a 7805 and I stuck 4 AA batteries under the nose for the regulator. I took the unregulated 6 volts to the motor pin on the L293D.  So the BOM is something like:

Tamiya gear set:  14.95 Protoboard: 7.00 (www.jameco.com - get a JE23) L293D: 4.00 (www.wirz.com) 74LS367: .90 (www.digikey.com) EIA adapter: 4.95 (Radio Shack - but get it elsewhere cheaper) 4 AA batteries and holder: 3.00 (?) LED with Resistor (on the first port - just to watch): .70 Handful of tie down resistors (4.7K): 1.00 .1 uf Caps for motors (one across each motor terminal): 1.00 470 uf Electrolytic for regulator: .70 .1 uf Cap for regulator: .70 wire, sticky tape, rubber bands.

Total cost if you have to buy everything above is about $40.00. If you have an old gear set, protoboard, or don't want to use the EIA adapter (just use a 25 pin male connector and run some wires from computer to the protoboard), you can trim it to less than $30.00 (plus shipping <grin>). If you already have a PIC ROM burning setup, you can put a PIC on board and run the whole thing autonomously for about the same price.

Larger picture of Cheap1
 Real Media of Cheap1 (67k) - must have latest Real Media player
 Close up of Cheap1's Butt
 Close up of the prototype area for Cheap1