---------------------------------------- > Date: Wed, 9 Jan 2008 23:30:40 -0800 > From: [EMAIL PROTECTED] > To: [email protected] > Subject: relay computers > > > I have long thought it would be cool to build a simple computer out of > transistors, vacuum tubes, or relays. Not only for the educational > aspects but also for the art of it. And to demonstrate that a computer > is not magical. It is a machine just like any other. A very complicated > one. But a machine all the same. Transistors themselves almost seem > magical so they are out. Vacuum tubes are expensive and potentially > failure prone. But relays seem just right. They are mechanical devices > that people can understand. Put enough of them together in the right way > and you can actually make a semi-useful computing machine. >
Transistors aren't that bad. The trick is- use transistorsto make gates. Its pretty simple. Take 2 CMOS transistors, 1 ptype and 1 n type. Connect the ptype's source to high through a resistor. Connect the ntype drain to logical low. Connect the input to the input gate of both gates. Connect the source of the ntype and the drain of the ptype, this is your output. his is an inverter. (note: in pure CMOS, you don't use a resistor- you use a 2nd transistor with logic high going into both source and the input gate). Now take 4 CMOS transistors- 2 ptype, 2 ntype. Put the ptype in series, so the drain of one goes into the source of the other. Connect the source of the other through a resistor to high, Put the ntypes in paralel with drains going to low. Connect the ntype sources and the drain of the bottom ptype. This is your output. tie to gether the inputs of the ntype and ptype into 2 pairs of 1 n and 1 p. This is a nand gate. With nands, you can express any boolean expression in 2 levels, so you have all you need. Transistors are really only hard until you use the right abstractions. If you are in a digital circuit and always connect to high/low correctly, 90% of the difficulty goes away, and you can use the SR abstraction- the resistor is a switch, which when flipped on becomes a variable resistor. Gabe _________________________________________________________________ Get the power of Windows + Web with the new Windows Live. http://www.windowslive.com?ocid=TXT_TAGHM_Wave2_powerofwindows_012008 -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-lpsg
