Led Matrix question

[mhserrano]

Hi good-afternoon,

I´ve finished to build my first protoype board using IOW40 and 2 drivers MIC5891 and MIC5821.

When i connect the board into USB port of my PC it is imediately recognised and, for example, the switch matrix works quite well.

On the Led Matrx side seems to exist some problem, however i just have made very tests and confirmations about wiring and i think its all properly mounted.

Just see this example:

I´m using (excellent!!) ALL-in-ONE test program to give instructions to IOW40 to light up, for example, an 8x8 matrix. When this instruction is activated i dont have any voltage between ground and the output pins of the drivers IC´s. This is normal? It seems there is no activity.

My target is to drive 3 Seven Segment Displays (Common Cathode) together.

I´m not sure if i made the correct calculations for the Resistences of column drivers, i dont have the driver forward voltage value, needed to do the calculations.

Thanks in advance, all help will be great :)!!

Bye,

Marco Serrano

[Guido Körber]

No voltage between which driver and ground? Did you write any data into the matrix? If no LEDs are on you will see no outpur voltage on the sourcing drivers.

[mhserrano]

I´ve measured between MIC5821 output pins and ground.

I´m using All-in-one test program to send this instructions:



I´ve tested just some led´s activated too.

I´m using 100 ohm resistence at 5821 output.

Thx in advance,

MS

[Guido Körber]

The5821 are the low side drivers, you sould see a low voltage level at those outputs, if no current is provided by the 5891 then you will see 0V at the 5821.

[mhserrano]

Ok Guido, thats right, thanks for your answer, but i still cant light up any led! I´ve tried with very types of leds and no one have just a litlle light!!

I dont know what is going wrong. Is it necessary to have all the 8 resistors connected to the 8 ports of 5821 the circuit work properly? I just have already 4 soldered.

Thanks in advance,

MS

[Guido Körber]

The drivers do not really care if and what you connect to their outputs. This sounds like you did miswire something. Where are you getting the power for the high side drivers from?

[mhserrano]

I´m sending 5V directly from the IOW40 Vcc line to MIC5891 pin number 15 (Vdd, logic supply), like AN1 sheet picture suggests.

I´ve measured between groud and pin 15 and have 5V even without any instructions to be sent to IOW40 to activate led matrix.

Pins 2, 3, 4, 16, 15 and 14 from MIC5891 have 5V.

Pins 1, 2, 4, 6 and 7 from MIC5821 have 5V too.

Bye,

MS

[Guido Körber]

And where does the power for the high side driver come from? i.e. 5891 pin 13?

[mhserrano]

I dont have this pin number 13 wired!

I read on AN1 sheet that in small assemblies with moderate brigthness for the LED´s it is possible to supply from USB.

If i want to drive 5891 from USB i must put Vcc line from IOW40 on pin 13?

Bye,

MS

[Guido Körber]

Pin 13 on the 5891 is the supply for the driver stage of the chip. How is the chip supposed to know what we wrote in the technote? Whatever power source is used needs to be connected to this pin.

[mhserrano]

Ok Guido, problem fixed, led matrix is running smooth and fine!

Thanks for your help!

By the way, just confirm something:

If i want to give more power to the matrix, outside USB, i must put more DC voltage on this pin 13? Is it correct?

Thanks, bye

MS

[Guido Körber]

Yes.