Published 13 Jun 2021

DEC H-500 Computer Lab


Overview

To help train electrical engineers in digital electronics Digital Equipment Corporation (DEC) produced a digital logic trainer together with a training course. It allows students to connect up various configurations of basic logic gates following a workbook to get a hands on idea of what it was all about.

H-500 overview
DEC H-500 Digital Logic Trainer

There is a 110V version (H-500) and a 240V version (H-500-A), but all the logic runs on 5V. It came with a Computer Lab workbook (item B-350) and an assortment of 107 patch cords of assorted lengths from 2.75” to 24.75” (item “916”). There was also a Computer Lab Teaching Wall Poster (24” x 36”).

H-500 Computer Lab Poster

Hardware description

The logic gates are provided by 12 TTL logic chips: 7473, 7400, 7420, 7450, 7400, 7473, 7473, 7410, 7420, 7450, 7410, 7473. The chips are mounted on the under side of a PCB (item H500 PATCHCORD PANEL5004577 5404576B). There is a separate PCB containing the input switches, output lights, oscillator, and power supply (BEWARE mains voltages are present on this board).

There are 8 rocker switches for providing logic 0 or 1 inputs, and 3 momentary rocker switches to provide pulsed inputs. Additionally there is also a variable resistor control for an oscillator that has 6 selectable clock ranges, 3 “fine” and 3 “coarse”



The patch cords are colour coded according to length: ASCII

ColourLengthQuantity
Brown2.75”20
Red4.75”30
Orange6.75”25
Yellow8.75”20
Green16.75”10
Blue24.75”2

And they have uncommon tapered pins crimped onto each end:

ASCIIASCIIASCII



I've got two versions, one with light bulbs as output, the other with red LEDs. I'm not entirely sure whether the LEDs were a standard version, or whether someone has retrofitted them (possibly to replace failing light bulbs).


DEC H-500 schematic


Examples

Example 1

DEC H-500 label DEC H-500 label

DEC H-500 top view - LEDs DEC H-500 bottom view

DEC H-500 label DEC H-500 label

DEC H-500 disassembled view

DEC H-500 inside view

DEC H-500 mounting batten DEC H-500 mounting batten

DEC H-500 led


Example 2

DEC H-500 label

DEC H-500 top view - incandescent

DEC H-500 inside view

DEC H-500 light



References and Additional Resources

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