smaller HP 82166A with 32-pin connector

[Klaus Overhage]

   
   
I wanted to see whether I can switch an LED on and off with GETO. I would have loved to use GETLO for on and another output on the HP 82165A for off, but apart from the 16 data lines and 6 handshake lines, there are no other output lines on the HP 82165A. With 34 instead of 25 connections, the HP 82166 simply has more.

But with GETO first switch an LED on and then off again, that's possible. While looking for a 74LS74, I came across a 7474 with no letters in between. Didn't know that these TTL-ICs are also available without letters, is probably an early version, but behaves exactly like a 74LS74.

The data input PIN 2 of the 7474 was connected to the converted output PIN 6. At PIN 6 there was also a red LED against GND via a 330 ohm resistor.

The GETO output of the HP 82165A was connected to PIN 3 of the 7474. With each pulse on GETO, the level present at PIN 2 is saved in the 7474 and output inverted at PIN 6. So that it works, GND on PIN 21 of the HP 82165A must be connected to GND (or -) of the breakboard. Finally PIN 7 of the 74747 to - and PIN 14 to +5V, done.

The ittle program became one extra row:
01 LBL TRI
02 LBL 01
03 TRIGGER
04 STOP
05 GTO 01

Now it stops after TRIGGER puls GETO to low and the LED switch on. After pressing R/S TRIGGER puls GTO again and the LED switch off. And so on.

In my experiments the LED was off after switching on the voltage to the breakboard. Switching on and off by pressing R/S on the HP-41 worked without any problems.

We need more rain....