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I am thinking of purchasing an LTS4680 seven segment display for one of my projects.Here is the datasheetdatasheet:http://www.icpdf.com/icpdf_datasheet_7_datasheet/LTS4680AE_pdf_1732299/LTS4680AE_datasheet.html

I understand that it is a common cathode 7 seg display, so ground should be connected to the common cathode pin.What pin is it?I'm not sure but i think it's pin 6 according to the diagram in the datasheet.Also what value of resistors do I need to connect to the anode(+) of each segment.My power supply is 5v at 0.6A(600mA).

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  • \$\begingroup\$ Instead of connecting resistors to each segment(the anode of each segment)can't I just connect the resistor to the common cathode.Would the resistor value be different?Sorry, I am completely new to this stuff. \$\endgroup\$ – zack1544 Oct 3 '15 at 0:46
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    \$\begingroup\$ if you use a single resistor on the common lead, the brightness of the segments will vary, depending on how many segments are lit. \$\endgroup\$ – Peter Bennett Oct 3 '15 at 0:58
  • \$\begingroup\$ Ok so I'll just stick to connecting the resistors to the anode of each segment. \$\endgroup\$ – zack1544 Oct 3 '15 at 0:59
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According to the data sheet, pins 1 and 6 are both connected to the common cathode. The data sheet also specifies a segment drop of 2 volts at a current of 20 ma. Therefore, you should chose a resistor to drop 3 volts at 20 ma for a 5 volt supply. That resistance is 150 ohms. You may have to adjust this slightly since the data sheet values are only nominal. However, there is a maximum specified current of 25 ma per segment which you should be careful to avoid exceeding.

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  • \$\begingroup\$ Can I just connect two 220 ohm resistors to each common cathode pin?Would 220 make the display too dim? \$\endgroup\$ – zack1544 Oct 3 '15 at 0:56
  • \$\begingroup\$ Disregard my last comment.Can I connect 220 ohm resistors to each anode pin of each segment? \$\endgroup\$ – zack1544 Oct 3 '15 at 1:00
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    \$\begingroup\$ @zack1544: You should connect one resistor to each anode pin (on a common cathode display). The exact value to use depends on how bright you want the display - higher value = lower current = dimmer display. LEDs are not fussy about the current, as long as it doesn't exceed the maximum rated current. \$\endgroup\$ – Peter Bennett Oct 3 '15 at 1:03
  • \$\begingroup\$ Oh I think I get it now.So I need to use a resistor of at least 150 ohms, connected to each anode pin of each segment. \$\endgroup\$ – zack1544 Oct 3 '15 at 1:07
  • \$\begingroup\$ Thank you Peter and Barry, for both your responses.I finally understand what I have to do. \$\endgroup\$ – zack1544 Oct 3 '15 at 1:09

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