Wednesday, April 27, 2011

Cleaning house part 3

Some of the external experiments that used the PC or Apple i/o cards were found during clean up. Above is a stepper motor driver controlled directly from an Apple II i/o card.
This is a temperature probe that uses op-amps and an A to D converter for rather accurate T measurements. The probe is a 2n2222 epoxied into the end of a pen barrel.
.... not sure but lots of familiar parts!
Digital dice made using wire wrap technology.
A binary number game. The black header holds a 7 segment display driven by a random number generator. The student would set the DIP switches to make the same number in binary and push the button. The circuit will indicate Too High, Correct or Too Low.

These circuits are now trash but the memory of making and using them in classes remains.
Sniff :(

Cleaning house part 2

This hand made PC ISA slot interface card used the 8255 chip to provide three 8 bit digital i/o ports. The DIP switch is part of setting the address of the card. A 25 pin (D sub) cable connected the card to an experimenter card made using the same wire wrap technology as the interface card.
These experimenter boards gave the students 8 LEDs, a 7 segment display, 8 DIP switches mounted on the white header and access to 8 i/o pins via the terminal strip to connect external circuits and experiments.

Part 3 shows some interface circuits and other random circuits made in the 90s.

Cleaning house part 1

We're cleaning up our classrooms in preparation of a move to a new building with more limited space. I came across these old computer interface circuits we used to employ when I taught electronics back in the 90s.

These first two photos show one of the Apple II interface cards we used. These were made using wire-wrap technology. Each card provided two 8 bit digital i/o ports labelled A and B. We would use a ribbon cable like this:
.... to connect to a hand made experimenter board like this.
Here students could control the LEDs or read the position of DIP switches mounted on the white header.
In part 2 I'll look at the next generation . . . PC interface cards.