Hi! Iv'e posted a little bit about this before, but I need a solid answer. I couldn't find a specific answer on Arduino Playground - MAX72XXHardware
So I am using the Max7219 ic to control an led clock with the help of a ds3231. I need help with the Rset. I am using leds that take 20ma, but there are 28 leds in each segment max (7 leds max in each segment in a digit). Does the Rset mean that each segment can only have 20ma? (One led) I need a confirmation that I wont completely kill all the leds in my clock and it doesn't really matter the amount of leds in a segment. I can supply 2.4 amps max. I am very new to this stuff. Thanks so much, your replies really help me out!
Table 11 is your friend. Iseg is segment current, so find the 20mA line and match up to your LED's forward voltage and you will find the resistor value for RSET. (The values given in the table are kOhm, btw)
To steve: I understand that, but my segments will have WAY more than 20ma in them. I need a conformation that it will work with all the current not just 20ma. Also ya sry for the double post
Rapid80:
,but there are 28 leds in each segment max (7 leds max in each segment in a digit)...
Doesn't make much sense, but it seems you picked the wrong chip.
The MAX7219 can only drive segments with single LEDs, not strings
(assuming you mean several LEDs in a strings).
Post link or a diagram of the LEDs in one segment (series/parallel/Vf of the LED).
Large displays with multiple LEDs per segment are commonly driven by TPIC shift register chips. One per digit.
The TPIB6B595 (ebay) can drive a long string, with currents up to ~150mA.
Leo..
I think I am about to be extremely sad, but one question. For four digits, there are 4 "A", "B", "C" etc. segments. does the 20ma mean in a segment PER digit? I think I am about to be distraught.
This what I have so far. There will be four of that first digit. You can see the seven segments.
That display might be a big blur when many segments are turned on.
For comparison, here are 3-LED segments viewed from ~ 20 feet away, spaced out farther than yours.
Well, maybe not further, but certainly not as dense. These are 3 LEDs in parallel per segment. All LEDs came from the same batches, and I didn't have the current set so high that if one LED in a digit failed (open hopefully) that the other 2 couldn't handle the extra 1/3 of current from the failed LED. None ever failed tho in 10 years of on/off operation for several hours at a time, several times a week.
Also, in each individual segment, all the postives are connected and all negatives for that whole digit are connected. Common cathode. Would this design for the circuit work? DIY Digital Clock Homemade - YouTube I'm still worried about current and all that. This is the first time i've done something like this.
One piece of advice on nomenclature. You keep referring to “segments” when I think what you mean is “digits”.
A “7 segment display” is called that because each digit consists of 7 individual LED segments (think of the 7 straight lines that make up the numeral “8” on an LED display”.)
So your use of “segment” in the earlier posts was a bit confusing.
So are you designing a display that uses a 7x4 LED matrix to display each digit? And how many digits total?
This is what I have with the Max7219. You could do similar with your 6 or 7 LEDs in parallel to the Max7219, and use the current limiting of the Max7219 to control brightness.
