Author Archives: Eric

Parts from Digi-Key arrived a day early

Thanks to Digi-Key and UPS, parts for my RetroChallenge project arrived a day early. I just got back from my client’s product launch party, where I had entirely too much excellent food and drink, so I’m not actually taking advantage … Continue reading

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Schematic and PCB layout finished, boards ordered

Late last night I finished the schematic and PCB layout, and ordered boards. As soon as I woke up this morning I realized that I forgot to deal with the 5V CMOS output of the TIA-232-F receiver feeding the non-5V-tolerant … Continue reading

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RetroChallenge Half-TIme Report

Although I got the LTP-305HR dot-matrix LED multiplexing working, it doesn’t look anywhere near as nice as the original HP 5082-7340 or TI TIL311 hexadecimal displays. I’ve decided to drop my original plan to use the LTP-305HR displays, and use … Continue reading

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Full multiplexed display for RC2017/10

I’ve now got full multiplexed display operating on the breadboard prototype for my RC2017/10 project: I also shot a brief video showing chaning hexadecimal values. There are six 5×7 displays, physically all in one column to fit the breadboard, but … Continue reading

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RC2017/10 finished wiring LED matrix

I finally finished wiring the LED displays on the breadboard prototype. What a mess! The LTP-305HR displays are still being driven basically statically, with only one column of LEDs (on both logical rows) being illuminated at a time, and only … Continue reading

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More LED matrix prototyping

I’ve added a second breadboard to prototype with all six LTP-705HR displays, and the additional sink and source driver needed. The matrix is wired, but not all of the drivers are hooked up.

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FPGA-Elf display drivers and multiplexing

For my previous FPGA-Elf, I used actual hexadecimal displays as per the Popular Electronics construction article. The only hexadecimal LED displays still made are from Broadcom/Avago, don’t have the integral red filter, and cost around $40 each. Used or NOS … Continue reading

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RC2017/10 project: affordable FPGA-Elf

For the RC2017/10 RetroChallenge, I will update my FPGA-Elf to run on a relatively inexpensive FPGA board, and make PCBs to provide the necessary I/O interfaces.  I plan to add the equivalent of the CDP1861 “PIXIE” graphics. At the conclusion … Continue reading

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unintentional nondeterminism in a Python program

There’s a Python 3 program I’ve been developing off-and-on for three years now. The program takes an XML file as input, does some processing, and outputs a binary file.  After some recent changes, I find that the program hangs. If … Continue reading

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Vonada’s Electrical Engineering Maxims

A list of electrical engineering maxims by DEC Engineer Don Vonada: There is no such thing as ground. Digital circuits are made from analog parts. Prototype designs always work. Asserted timing conditions are designed first; unasserted timing conditions are found … Continue reading

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