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Really looks like a textbook RS-485 interface: With the DC-DC converter to provide isolated +5V, three opto-isolators (white packages) for Tx, Rx, and Tx enable, and a bus transceiver (U6). The two connectors could be to facilitate an RS-485 network daisy chain connection. Certainly would...

If you want to get fancy, you can make your own LDO: This circuit is from here: http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/70729/256693 The trick is to use a depletion mode MOSFET, for example an IXYS IXTP6N50D2. The depletion mode FET will be normally turned on...

IEEE-488 to RS232 converter for the PET? From The Silicon Gulch Gazette:

From Season 1, episode 12: The PET in the travel agency office.

This is from Season 1, episode 6: Looks similar to a VT100 terminal. In the travel agency there are some PET looking computers. They seem to paint them over and/or remove logos. There are some teletypes, tape drives and lots of vintage items throughout the series.

I can't agree. From the National Semiconductor LM78XX datasheet: "It is not necessary to bypass the output, although this does improve transient response." The problem is that the 78xx cannot respond fast enough on its own to a fast change in output current (which I assume is what you mean by...

I just noticed this maybe old news, Todd Fischer is putting his IMSAI up for sale: http://www.itworld.com/security/362522/buy-matthew-broderick-s-old-movie-computer-possibly-impress-ally-sheedy www.imsai.net seems to be down at the moment for some reason.

I was visiting a local company yesterday, and noticed a machine using 8 inch floppies:eek: So I took a crappy picture with my cell phone: It's a FETTEST 9300B, for testing semiconductors. Usually, as in this case, it is connected to a wafer prober. The disk sleeve says Radio Shack...

Interesting article in IEEE Spectrum: http://spectrum.ieee.org/computing/software/did-bill-gates-steal-the-heart-of-dos/1 Written by a vintage computer collector, maybe a member here? The article is something of an ad for his forensic tools. He tries to determine if DOS was copied from CP/M...

Huh? Tying the enable to high won't work. Using the address lines probably won't work either, so your 8 bit code won't work. Your 4 bit code looks like you are not pulsing the E line. Here is a timing diagram from the HD44780U: You have to pulse E. Transfers only happen when E goes from...

I noticed that the MITs Altair documentation and some of the ads use the word buss instead of bus. Did any other manufacturers use buss? Or was this just the occasional odd spelling or maybe misuse of the word? Then there's disk and disc...

I noticed that the LM339 datasheet does show a single power supply zero crossing detector: This is inverting, otherwise you have to swap the + and - input (except the 20M feedback resistor needs to go to the + input). This circuit depends on the resistors to be balanced on both sides to switch...

For a single supply with AC coupled signal to a comparator, you can do this: You may want to add a large feedback resistor from output to positive input for some hysteresis. Most of old bipolar op amps and comparators have a limited common mode input range that doesn't go all the way to...

An Arduino based KENBAK-1 replica has been popping up on the tech blogs: http://www.funnypolynomial.com/software/arduino/kenbak.html

I while back I was at the local surplus place (HSC), thinking about switches to make a front panel for my hobby project [http://mini-altair.tripod.com/], and I noticed a bin with paddle switches. They looked like IMSAI switches, so I grabbed a bunch of them. They were all red, but they also...

I thought some folks here might be interested in a hobby project I worked on and wrote up here: http://mini-altair.tripod.com/ (Sorry for the ads.) It's an 8085 single board computer intended to be compatible with the original Altair software. It runs all the Altair BASICs: 4K, 8K, 12K...