[cctalk] Re: VT100 Monitor Board

-----Original Message----- From: Dave Dunfield via cctalk <cctalk(a)classiccmp.org> Sent: 25 November 2023 14:06 To: cctalk(a)classiccmp.org Cc: Dave Dunfield <1297.dunfield(a)gmail.com> Subject: [cctalk] Re: VT100 Monitor Board An older CRT terminal is probably a bit too much current draw for this, but you can prob use it in a setup to test parts... A very handy gadget you can make very easily, which I use all the time when testing small devices in "unknown operational state" is a simple current limiter. (following discussion based on North America power, numbers may be different if you are in a different part of the world). The "smallest" typical line circuit is 15A which is more than enough to cause damage to small devices experiencing excessive power draw through a fault (often indicated by a blown fuse). The "limiter" relies on the fact that an incandescent light bulb will draw/pass a fair bit of current when it is cold, and much less when it's warm. (this is because they are designed to "turn on" fast)

In my case, I have three light sockets wired in parallel, all in series with the hot side of a receptacle. This lets me change from a single 25w bulb (very little current possible) up to 3 100w bulbs (a good part of amp before it seriously limits). For example, 100w bulbs draw .833ish (100/120) when operating fully lit - x3 = 2.5A max current - this would only happen if the device under test was "shorted", presenting 0 series resistance and would therefore effectively have 0 volts across it. In practice, you could prob. draw 1/2 amp (160ish ma per bulb) without warming them "too much" to seriously drop a lot of voltage. Much more than that and the bulbs will light up rather than hearing "popping" sounds from the device under test :-) -- Btw, I've given most of my CRT terminals away - For VT100's I use my "PC100" program - It provides very good VT100 emulation using an old DOS (or DosBox) PC - it remains "text" mode, so it turns "smooth scroll" into "slow scroll" and large fonts into "double spaced" fonts - but in all other respects nothing I've used it on has been able to tell it's not an actual VT100! (I'm sure there are better/graphical VT100 emulations "out there") Dave -- ---------------------------------------------------------------------------------- Search "Dave's Old Computers" see "my personal" at bottom!