Homebrewing a classic

Some thoughts on this homebrew stuff... Front Panels: ------------- I've been mulling over the idea of building a "generic" front panel. Clearly there is a lot of resonance with the blinking lights of the PDP-series, the Altairs and IMSAIs etc. However if I did this it would have to be both durable and cheap. Having rebuilt a couple of PDP-8 KC8's I think the rocker over the slide switch can be cheap but it isn't durable. I've been sketching ideas based on a rocker that is threaded on a rod. The back of the rocker contains a 'paddle' which when the rocker is down, breaks an IR/detector gap. This has a couple of benefits. One the rockers are on a rod so they don't have small pins to break off, and two the switch mechanism is optical and thus not subject to oxidation decay that mechanical systems suffer. Of course I would like the front panel to be usable for a variety of hardware designs and that leaves open the question of 'generic' switches. Clearly there are the following switch requirements: Run/Stop Single Step - momentary Deposit - momentary Examine - momentary Load Address - momentary switch register - what size? Could have 8 to 32 bits if we wanted Key switch - Off/On/Panel Lock Some panels adopted a dual action switch for 'examine'/'examine next' and 'deposit'/'deposit next'. Clearly that's harder to do with my simple optical switch. Compound Computers ------------------ I've about half decided to build something PDP-8 like out of PIC chips. They are relatively cheap, easy to program, and quite fast. I hadn't thought about using them as base units (microcode sequencer, ALU control, etc) until this discussion began, but it also raised the point of 'emulators' and I began to wonder what if you build a Z80 system that emulated a PDP-8 with one of these custom front panels. That turns out to be more of a software effort than a hardware effort. Transistor based CPUs ---------------------- You can get PC boards made fairly cheaply, if you wanted to do a transistor based CPU I would definitely consider having a few hundred 'flip chip' equivalents made. It wouldn't have to be 1:1 DEC replacements but they showed it could be done. Wiring up 12 flip flops by hand on a piece of perf board (4 transistors each!) would be extremely painful. TTL Logic based CPUs -------------------- First, find a 50Amp 5 volt supply. :-) The thing about TTL logic that always amazes me is how much power it draws. I built a digital PLL out of TTL chips once (about 40 chips) it was easily drawing 3-4 amps at speed. 74HC logic might be a good compromise here. The use of CRTs --------------- There is a really clever homebrew display that was influenced by early computers called the 'beer budget graphics display' and was featured in BYTE magazine in the late 70's. Basically this was two R2R D/A ladders driving the X/Y inputs to an oscilloscope. If you make a 12 bit machine you could build a 4K x 4K resolution display fairly easily. (You will be core limited in terms of points to plot but what the heck right?) This type of output was featured in several different early computers. Anyway, just some thoughts... --Chuck