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Author Topic: 7 segment resistor  (Read 433 times)
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what value resistor is proper for the 7 segment display?
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nr Bundaberg, Australia
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What is the driving voltage, forward voltage of the segments, and required current for each segment?

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Rob Gray aka the GRAYnomad www.robgray.com

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You can calculate the resister value with below link, but you need know voltage drop and led current.

http://www.hobby-hour.com/electronics/ledcalc.php
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It also depends on if you are multiplexing the display or not.
Multiplexing means you can push the current higher than if you are not.
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considering it's "resistor" not plural, perhaps the OP is using a driver chip like the MAX7219 which uses just ONE resistor ?
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Or a single one on the anode/cathode.

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All the calculations aside, if you are operating at 5V, a 470 ohm resistor will allow 11mA (rounded) which is almost always totally OK.  In fact, it will be even less than that because of the voltage drop.  If you want to just approach this problem empirically, try that  resistance and if you are not happy with the brightness, substitute resistors with less resistance until you are happy.  Probably it would never be a good idea to go lower than 200 ohm unless the LED allows for higher than usual currents.  This all assumes you are using a breadboard, of course.  If you are soldering it, this might be a poor way to approach the problem.
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