# WOW!!!! \$15k DEC PDP-8 CLASSIC MINICOMPUTER SYSTEM DIGITAL PDP8

Tony Duell ard at p850ug1.demon.co.uk
Fri Jul 8 17:45:12 CDT 2005

```> Figuring out alien unmarked and complex resistor networks is a nerds
> treat.  It's a mathematical puzzle in physical form.

I am not sure exactly what a 'nerd' is, but on the grounds that I enjoyed
working this out, I guess it makes me one.

[If you assume that all resistors are pin-to-pin, with no internal
junctions, which seems to he good for the HP DIP networks, then you can
deduce the resistors and connections by :

1) Measuring the resistance from each pin to all the other pins shorted
togetner

2) Shorting all but 2 of the pins together (and call that 'ground'), then
apply a known voltage to one of the leftover pins and measure the votlage
on the other odd pin. Calculate the voltage division ratio.

The first gives you the effective resistance of all the resistors to a
given pin connected in parallel. The second gives you the ratio of one of
the resistors to all the others in parallel. From that you can calculate
that resistor.)

-tony

```