UroBoros
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blueroomelectronics said:...with 470ohm resistors. But your design is driving the cathodes directly from the PIC and that's not enough for most typical displays. Add a 1.2K resistor and a 2N2222 will allow you to properly drive most displays. Check the Dragonfly schematic on my site for details and a program to test it.
1. 330 ohms resistor is ok.Picstudent said:Hello
I am doing a system with 8 numbers of 7 segment digits. common cathod ,directly driven from PIC port pins. Usually for systems with 4 digits what I do is a use a 300R resistor series with MCU port pins and timing I adjust by trial and error and it used to be ok.
<snip>
IanP said:Try this:
In other words, for 1/8 mark-space ratio, you will have to allow 40mA pulse current per segment and, in the worst case, when all 7 segments are on, the cathode driver has to sink pulse current of 7*40mA ..
Regards,
IanP
This is not a good idea at all. You will be damaging the drivers.nandhu015 said:Dont use any resistors.
As you are switching at higher speed you need lot of inrush current.
nandhu015 said:Dont use any resistors.
.... you need lot of inrush current.
Regards
Nandhu
If LED's can take a steady current of 20 mA, then they can take a peak current of about 100 mA (depends on the LED and also on the duty cycle). Current limiting resistor is a must.Picstudent said:Still a limit is to be fixed depending on the size (which determins the voltage) of display.
I am using limiting resistors, not yet tried without them.
sn_burki said:I also want to know that how to calculate current of scan led with duty cycle??
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