MAX7219 LED RSET

Other Hardware LEDs and Multiplexing
1

Hello everybody!

I'm currently trying to make my own led tail light based on some MAX7219.

My problem isn't based on the programming, as i tried it on a simle 8x8 led matrix with success.

I was just now trying to wired my own MAX7219 with a few led to test it befor slodering it and it's not working!

The wiring is as shown on the datasheet,

+5V => Pin 19
GND => Pin 4 /9
DIN => Pin 13 on the arduino
LOAD => Pin 10 on the arduino
CLK => Pin 11 on the arduino

I'm using the Ledcontrol.h, it was for this, only blinking the 8 Led at SEG DP and DIG 1-7

This is normal Red 5mm leds for this applciation with RSET 10k Ohm(normally i will use Superflux led with 27K ohm)

When i didn't put any RSET resitor, all the led is blinking but i can't set any intensity and i don't think it should work like that.

When i put the RSET resistor, all the led stay on, and nothing happened.

I try another MAX7219, many resistor value(10-30K Ohm), many other led, but it not seems to work...

Even if i try with the Demo program, with only 8 led nothing happened to them

What is wrong in your mind? I try everything that i supposed but unsuccesfully.

Thank's

2

Please post a schematic - do you have the Cathodes wired to the DIGIT pins, and the Anodes wired to the Segment pins?
Do you have a 10uF and 0.1uF (or 100nF) connected to the Vcc pin?

3

Hi thanks a lot for your answer!

Finally you got it.... i was aiming for the light to be on when i plug it so it was reverse :confused:

If i want to have both tail light of the car (About 2m wires) to be synchronised, how can i do this? Except by wiring 64 led though the car lol

4

Have a Max7219 at each location running the local matrix and tell them all to do the same thing at the same time. This only requires 3 signal and 2 power wires. I would wire them all up in series cascaded through the Din Dout.

5

marco_c:
Have a Max7219 at each location running the local matrix and tell them all to do the same thing at the same time. This only requires 3 signal and 2 power wires. I would wire them all up in series cascaded through the Din Dout.

Yes i thought about it but with the wire lengh, it could create some issue right?

6

Yes but less issues than if you had 64 wires. You may need to add some buffers to boost the signal. If installing in a car you may also have to deal with an electrically noisy environment if you use the car's power circuit.

7

Ok then what could i use too boost the signal? I don't even thought about it at the moment...

I have my led which seems to be really dimmed compared to what i have ahead with a normal resistor at 20mA...

This is "superflux like" led, i used them with 20mA so (470Ohm at 22v for 6 led), the forward voltage is about 2-2.2V

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If im refering to this documentation from the datasheet, with RSET@10kOhm and a fw voltage of 2.2V i should have 47 mA on the led at full power.

I set the "lc.setIntensity(0,15)" so at full intensity, the led seems a lot less brighter that the one i'm using at 20mA with resistor. I mesure the current @22mA with the resistor test .

The test isn't really correct if i measure it with my multimeters and the MAX7219 as it's not a perfect line signal right?

Thank's

8

Correct, the 8 columns of the matrix are multiplexed at 800 Hz, so you can't read the signal across the LED with a meter.

Did you set the scan limit register as well?

9

I didn't set the scan limit register for the moment, because i will use it with 64 led, i just want to simulate the system before soldering anything to not waste anytime after this.

For the scan limit, i have seen this but normally itonly impact on the frequency of the power output to the led?

10

Scan limit sets the number of digits that are scanned. This means, for example, if you only set 1 digit (8 LED) the 8 LED are scanned 8 times faster that if all 8 digits were on. If you set the limit to 4 then it scans 2x faster. Basically, no time is wasted on the digits that are not implemented. This means that the LED could appear brighter.

11

Yes but for my parts, if it's really at 40mA, why mine with 20mA seems a lot lot more bright?

That's a big issue as i can't do anything because of this low light output