Thursday, July 20, 2017

Testing complete for relay tester, ready to ship

I have been on vacation for a week, no posts or activity but returned to the workshop today. 


We are going to exhibit the Alto at the upcoming Vintage Computer Festival West event, as well as hosting a few panels. I will be on two of them, one concerning the restoration of the Alto and another concerning restoration of the 1401 systems.

This will require development and scripting of demonstrations as well as our material for the panels, but at the same time I want to begin using the disk tool I built to archive the stash of cartridges from Xerox PARC. The tool will also allow us to create disk cartridges to support our demo activity.


Having located the proper code and identified a few tweaks to make to the wiring in the box, I began the adjustments today. As I had earlier written, the four or six sets of contacts in a relay could be identified with ordinal numbers starting from either end of the relay, but I chose the incorrect end.

Rewiring those connections will give me a box that works properly with the unmodified code developed by Stan, thus keeping the two relay tester boxes in sync as future changes are made.

I ran the tester through its various functions, using a relay from our spares stock and found that I still have one flaw. I can individually drive the pick or the hold coil in the relay under test. The Arduino pulls down a wire for each that is connected to the dual relay module inside the tester. However, the relay modules only click on when both pick and hold wires are activated, not individually.

We reasoned that this is due to a short between the two wires driving the dual relays. If they are shorted, then one is outputting high and the other low if I try to drive only one of the two coils. This produces an intermediate voltage, not 0 and not 5V, which is too high for the dual relay module to fire either relay. When both are active (low), the wires are down at 0 and the relay module will click on.

I opened the box to locate and correct the short. With that done, everything is working correctly and this is ready to be shipped to TechWorks! for use with their 1402 reader/punch. I wrote up a user manual and will ship that along with the box. Stan is going to set up a laptop to ship with the box, allowing this to be a turnkey test system.

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