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View Full Version : WTB: CI-7 cassette interface cable for the TI-74 BasiCalc

smp
December 4th, 2017, 06:48 AM
I recently posted a request in the Wanted section:

Does anyone have the schematic for the CI-7 cable?

Thanks!

smp

January 7th, 2018, 12:57 PM
I'm wondering if we could easily make one.

Jim Brain has been helping us out with CC-40 peripherals lately. The 74 has the cassette stuff mostly built in.

Some folks on Stack exchange got a rudimentary interface going: https://electronics.stackexchange.com/questions/303291/saving-to-cassette-with-80s-basic-calculator-ti-74
Here's what the innards of the cassette interface looks like: http://www.datamath.org/Graphing/JPEG_CI-7.htm#PCB

Note that the interface is just a 74HC367 (3 state hex line buffer/line driver), a CA358E (Op Amp), and a bunch of caps, resistors, and transistors.

"Paolo" on the Stack Exchange discussion was on the right track for a home-brew adapter: http://www.datamath.org/Graphing/JPEG_CI-7.htm#PCB

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I realized such an Interface severals years ago. The "Data Output" pin is pin #6 --> D3. The "Data Input" pin is pin#3 --> D0.

Recording:

you are on the right way: just use a voltage divider (e.g. 2 resisitors) to match the voltage requirements your recorder. A 100nF capacitor between voltage divider and mic-input could help.

Playback:

You have to clean and amplify the recorded signal, it must be a square wave, with low state = "GND" and high state = "VCC".

I used a common LM358N as non inverting Schmitt-Trigger to obtain a clean wave. It'easy, you need only 4 resistors. I played wit several resistor values, I obtained the best results with a 0,3V treshold.

You can supply the LM358N from Pin#1. Ok, it drains power, but not noticeably ;-)

I used the same interface with a Sharp PC-1260: VCC: pin#2, GND; pin#3, data in: pin#6, data out: pin#7

Have fun! :-)

Paolo
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