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Author Topic: CASIO calculator and Arduino; joining circuits of different Voltage  (Read 1197 times)
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Hello!

I'm trying to hack a CASIO fx-85ES calculator:


I want to use the calculator as a keypad (arduino knows what button you pressed) and display (arduino "presses" a button), using an Arduino Pro Mini (5v).

buttons are pressed by connecting two contact points on the board:

 for example: K07 + KI5 = "1" or K01 + KI2 = "4"
I only want to use the following keys: 0-9, +, -, x, :, =, and ")". total of 16 buttons

I plan to:
Connect points using transistors "press buttons". (is there a way the arduino can do this without transistors)
Use pins as input to read buttons pressed. (or more transistors?)

Note: I will only use calculator as INPUT OR OUTPUT never both at once.

Anything I forgot or suggestions? what do you think, could this work? smiley-razz
« Last Edit: April 21, 2013, 05:29:11 pm by RonaldPoFo » Logged

Barcelona
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Would I damage the arduino by feeding the contact points on the calculator to it as inputs?
Do I have to join GND like when wiring a Servo????  (1.5v cicuit of the calculator and 6v circuit of the arduino)
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It is not clear what you are asking.

You want to use the Arduino as a substitute for the keypad?
OK

And also to read the calculator's keypad (key strokes), when that is used?
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Barcelona
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I WANT:
An arduino Pro Mini 5v to:
-Know when a button on the calculator is pressed.
-Press buttons on the calculator(buy connecting two connection points)

HOW?:
Know when a button is pressed by reading a change in voltage between connection points.
Use transistors to connect two connection points, transistor's base (B) to arduino.

MY PROBLEMS:
Will feeding a cable from the connection points on the calculator to the arduino damage the arduino? or even work?
Can I join two connection points on the calculator using the arduino, not transistors? ( the two connection points have to be wired one to another, NOT to GND or Vcc)
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http://www.nxp.com/documents/data_sheet/74HC_HCT125.pdf

not sure if this helps
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What does this mean:
quad buffer/line driver with 3-state outputs controlled by
the output enable inputs
I tried goggling around but I don't see how it should help?
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it means you can use this chip to have 2 different components that use different voltage talk to eachother, ie 3.3v to 5v. its a buffer between the 2.
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Would I damage the Arduino by feeding input and outputs to and from it without any isolation? (transistor, optocoupler)
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using the 125? i really dont think you can,  a very good detailed explanation http://www.gammon.com.au/forum/?id=10990
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No, without using any kind of isolation.
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