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Author Topic: 4 digit 7 segment led circuit  (Read 859 times)
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Hi,

Could anyone please suggest me a circuit diagram for connecting a 4-digit seven segment LED to a mcu. I would be using the gpio lines to control the led display. I am using LM5654-11 ledtech display for my application. The datasheet is http://www.datasheets.org.uk/LM5654-11-datasheet.html.

I am basically looking at what are the components that needs to be present in the circuit.

Thanks,
Hwk
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The datasheet says that is a common cathode display, and it quotes the LED voltage for 20mA forward current.

See attached schematic. I have only drawn one digit driver (the 470 ohm resistor + transistor) - you will need four of these. Similarly, I have only drawn one anode drive connection (the 150 ohm resistor) - you will need 7 of these, or 8 if you want to drive the decimal point as well (but use about 470 ohms for the decimal point instead of 150 ohms, otherwise it may be too bright).
 
This uses 11 Arduino output pins in total, or 12 if you include the decimal points. The 4 digit driver pins can be also used to multiplex push buttons or rotary encoders (using diode multiplexing) at the same time. If 11 pins is too many, there are ways of reducing the pin count using extra ICs.


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Quote
I am basically looking at what are the components that needs to be present in the circuit.

Too  many ways to do it, depending on your requirement.

The most pin-intensive would be to use 8-pins to drive the segments, and 4 pins to drive the digits.

From there, you can use a shift register to drive the digits; or to drive the segments; or to drive both.

You can also use dedicated ics for that, further reducing the pin counts.
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As dhenry indicates, a MAX7219, $1.25 from taydaelectronics.com, will drive that part and use just 3 IO pins to do it. You wouldn't even need multiplexing software, just need to update a value in a register when there was a change. Need one resistor to set max brightness level, and a 0.1uF cap from its Vcc pin to Gnd.

* MAX7219-MAX7221.pdf (450.95 KB - downloaded 16 times.)
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