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# How to connect a 10 digit standard calculator display to a large LED display using minimum electronics? Answered

I am interested to display the output from a 10 digit standard calculator on to a large LED display panel that can be read from a distance of 20 meters. I have found instructions in this site on how to make a LED Display pannel. I now need to know how to connect this pannel to the calculator.

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Why not just use a phone or tablet to calculate and send the output to the LED?

its easy. LCD is AC. LED is DC. just convert the low ampere AC output from the calculator board to a higher ampere DC. use signal transistors like BC547... for a 10 digit calculator you may need 70 transistors. and 3 separate supply.

Its pretty difficult to do, without some very low level electronic skills. Calculator displays are usually multiplexed. That means there are 7 lines used to drive all the characters at once, and a line for each single character. A circuit is made between the 7 and 1, then the next character is lit with the same 7 and its unique line. You need to pick off, then amplify the LCD drive signals and use them to drive your other display. Which LED display are you using ? Steve

Thanks Steve,
Yes I was looking for a way of amplifying the LCD drive signals so that a LED display could be lit up.
I was planning to use a Instructable on this site "LED Matrix using shift Register" https://www.instructables.com/id/SCRTJ2OFH9HU7GR/ with some modifications as the Instructable is for a dot matrix LED board. I will be using the wiring instructions only with modifications for the 7 segments of each digit.
Clarence

Hi Clarencepinto,

Did you progress with your project?

I want to do the same but with a VFD panel and I need some ideas about the circuit.
Will you post your project (circuit and photos) here sometime?

thanks
john

You'll need massive modifications to your suggested design. It is fundamentally unsuited to what you need to do for a 7 seg display. By the time you have only 7 LEDs, and you've changed the display interface....