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Question on outputs tied together going into RGB LED matrix

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tdg8934

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I am designing an RGB LED matrix version of Sure Electronics 2416: 2416 Dot Matrix Green Display information Board_LED Display Panel_Display Equipment_MCU, Hobby and Display Modules_Sure Electronics' Webstore

I got the PCBs made from ExpressPCB and HT1632C ICs from Holtek directly. I found that if I solder 2 HT1632C ICs onto the PCB, the LEDs display nothing and the chips get pretty hot. 1 by itself works but 2 or more does nothing.

After troubleshooting all day and going through 2-3 PCBs and 9 HT1632C chips, I think I know the reason why it is not working and would like some confirmation to that please.

Each HT1632C has 24 cathode outputs. I am using 3 HT1632C ICs for red, green and blue LEDs and 6 RGB LED matrixes (common anode).
Each HT1632C has 16 common anode outputs. Theses 16 common anode outputs are shared by each of the 3 HT1632C ICs 16 common anode outputs.

If they are shared that means they are putting +5vdc on any of these 16 common anode outputs when an LED is turned on. This means that since the 3 HT1632C ICs have their 16 common anode outputs tied together going to the 16 common anode RGB LED matrixes, then that same +5vdc output from one HT1632C chip is actually INPUTing +5vdc onto the other 2 HT1632C ICs 16 common anode outputs.

Does this sound right? Is there a name for this so I can google it?

I supose my fix would be to have 16 * 3 diodes (IN914?) on each of the 16 common anode outputs so that the +5vdc does not get fed back into the other 2 HT1632C 16 common anode outputs.

Is there another solution?

I spent $200-$300 already on this project for a design flaw. Doh! The HT1632C ICs are fairly small and surface mount so I can't test on a solderless breadboard.
 

jimlovell777

New Member
What's the pinout of the LED's you're using? You say you're making an RGB display but are you using RGB LEDs or a single LED for each color?
 

tdg8934

New Member
Here a picture of what I mean.

I wasn't sure if everyone was exactly picturing what I wanted to do so I came up with a picture. This shows the diode approach instead of the transistor buffer (2 parts of transistor and resistor vs 1 part of diode only).

I just wanted to know if you think this would work. Currently I did not have the diodes in place and it caused the 2nd and 3rd HT1632C chips to overheat.

Comments?

Look at the last link at this post for the picture attachment:

Parallax Forums...
 
If I read it correctly, the slave chips would not have their anodes hooked up at all because they are controlled only by the master chip in your configuration. Said another way, by sharing the led module anodes, the slaves have given up control to the master, otherwise why use that configuration? Don't believe the diodes are the answer here, but a software fix might do it.

Where are the transistors and resistors? Are you multiplexing cathode on times? Looks like the package power rating could easily be exceeded without some of these precautions.
 

tdg8934

New Member
I see now that only the master uses the 16 comm output lines. Weird.

I guess it is controlled via SLAVE and MASTER commands somehow...hmm

The sure electronics 2416 project does not use transistor buffer circuits either.

All I am doing is making 3 of these (1 for red LEDs, 1 for green LEDs and 1 for Blue LEDs) all combined onto 1 PCB.

How do I know if I need to add these transistor buffer circuits or not.
 
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