So I’ve tried setRefreshRate(120) and still getting some flickering, but I think that may just be due to the jumper wires. I’ll try milling a board with short traces and see how that works.
However, when using Teensy 3.2, half the screen doesn’t work (two separate quarters), even though I’m using pin 15 now (PORTC). Switching to Teensy 3.6 and port 37, it does work properly. (I am changing ADDX_TEENSY_PIN_4 when testing between them).
Any thoughts?
You need to also change ADDX_PIN_4 in addition to ADDX_TEENSY_PIN_4. Teensy pin 15 is C0, ADDX_PIN_4 is 0.
There are other PORTC GPIO on the underside of Teensy 3.2 if you want to keep pin 15 free for something else:
30 C11
29 C10
28 C8
27 C9
Oh, I see the internal port numbers need specified. Got it, thank you!
I hooked up the supposedly 1/32 scan panel I have and started adding @pinballsp’s changes to the code, but quickly found that my panel is actually 1/16 scan. I placed an order for this panel on Aliexpress and hope to have it within the next month so I can make these changes and test.
@Louis ,
Have there been any updates on the new version of the library that would support 1/32 panels on the V4 shield? I plan to use a set of panels like @pinballsp, but I’m using your latest shield and I’m not sure if his code changes are compatible with the external flipflops (or did you use a counter?) that the V4 shield uses to drive the address pins on the panels. I just thought I’d ask before I start trying to implement 1/32 changes myself.
I just pushed changes to support 64-row /32 panels to GitHub. It’s not packaged up into a release yet, but you can download the code. I tested it on the 64x64/32 panel I received yesterday.
@samy commented on poor refresh rate when driving with the Teensy 3.2: that’s to be expected, it’s a lot of work for the Teensy 3.2 to refresh a 64x64 panel, and it’s even more work when it’s /32 scan and not two 64x32/16 panels strung together. The Teensy 3.5/3.6 should do better.
I didn’t add @pinballsp’s changes to support V1-V3 shields as there are more changes needed. I don’t want to break support for any existing users by driving a new pin unexpectedly. I don’t have the time to wire up a 5th pin on my Teensy, so I wouldn’t be able to test the changes myself. If someone really wants /32 panel support added to the library, and you can’t make the changes yourself following @pinballsp’s code above, please ask. There are other SmartMatrix Library features I feel are more important, like adding APA102 support, and getting the library ported to a platform with WiFi capabilities.
Thanks Louis. I started having a look at the code and although I’m quite well versed in C, I know very little about the DMA on the Teensy, so it was going to be a big job for me to try to get it working.
@Louis one last question. Do any code or circuit precautions need to be taken to make sure that the SmartLED V4 doesn’t drive the E address line high on a panel that is /16 and may have that pin tied to ground in the HUB75 port?
To be safe, don’t use set panelType to MOD32SCAN when connected to a MOD16 panel. I should probably put a current limiting resistor between the level shifter and the panel on the next rev of the shield, to prevent accidentally burning out that driver if accidentally driving that pin high when connected to ground.
I hooked up a SmartMatrix Shield V4 and Teensy 3.2 to a /16 panel that had the E line grounded, and had it run a sketch with panelType=SMARTMATRIX_HUB75_64ROW_MOD32SCAN for 8 hours. I switched back to a /32 panel after, and the shield was able to drive all the rows, so no critical damage to the driver after 8 hours.
Still probably a good idea not to use MOD32 paneltype on a /16 panel
I just received my matrices from China this week and I couldn’t resist adding one more reply to this thread. I now have a panel that is 256x64 functioning on the teensy. Gif playback is a little slower and I could only do 24 bit color refresh, but it works and looks better than I thought it would.
Now to find a clean way to mount these. 
Looks great! Thanks for posting
Hi all! I am currently working on a project and trying to connect two 64x32 boards (64x32 RGB LED Matrix - 5mm pitch : ID 2277 : $49.95 : Adafruit Industries, Unique & fun DIY electronics and kits), to form a 64x64 board. Although it says that the scanrate is 1/16, I have tried the FeatureDemo example on one board with SMARTMATRIX_HUB75_64ROW_MOD32SCAN and that worked fine. In the images the boards are next to each other, but I would like to create a square. However, the cables that I am currently using are not long enough for that. 
I am using a Teensy 3.2, with the 5th ADDX connected to pin 15 (PTC0). The others are connected to PTC1, PTC2, PTC3 and PTC4. I do not have a SmartLED shield and I hope that I can make it work without it.
I have changed the code as described above, but when I plug in the second screen, it does some weird things (see image). It copies the first screen to the second and only half of the rows are working. Also the letters are not displayed correctly.
Does anyone know what could be wrong?
Thanks in advance!
Hi, did you modify the SmartMatrix Library code to drive the 5th address pin?
Did you change the width and/or height in featuredemo drive the second panel?
I have made some changes to the code, I will list them underneath.
FEATURES DEMO
First line is commented out, width, height and kPanelType are adjusted.
// #include <SmartLEDShieldV4.h> // comment out this line for if you're not using SmartLED Shield V4 hardware (this line needs to be before #include <SmartMatrix3.h>)
#include <SmartMatrix3.h>
#include "colorwheel.c"
#include "gimpbitmap.h"
#define COLOR_DEPTH 24 // known working: 24, 48 - If the sketch uses type `rgb24` directly, COLOR_DEPTH must be 24
const uint8_t kMatrixWidth = 64; // known working: 32, 64, 96, 128
const uint8_t kMatrixHeight = 64; // known working: 16, 32, 48, 64
const uint8_t kRefreshDepth = 36; // known working: 24, 36, 48
const uint8_t kDmaBufferRows = 4; // known working: 2-4, use 2 to save memory, more to keep from dropping frames and automatically lowering refresh rate
const uint8_t kPanelType = SMARTMATRIX_HUB75_64ROW_MOD32SCAN; // use SMARTMATRIX_HUB75_16ROW_MOD8SCAN for common 16x32 panels, or use SMARTMATRIX_HUB75_64ROW_MOD32SCAN for common 64x64 panels
const uint8_t kMatrixOptions = (SMARTMATRIX_OPTIONS_NONE); // see http://docs.pixelmatix.com/SmartMatrix for options
const uint8_t kBackgroundLayerOptions = (SM_BACKGROUND_OPTIONS_NONE);
const uint8_t kScrollingLayerOptions = (SM_SCROLLING_OPTIONS_NONE);
const uint8_t kIndexedLayerOptions = (SM_INDEXED_OPTIONS_NONE);
MatrixHardware_KitV1.h
Added line 4 to define the 5th pin (at PTC0 in Teensy), changed last part of last line: 1 << ADDX_PIN_3 into 1 << ADDX_PIN_4.
#define ADDX_PIN_0 3
#define ADDX_PIN_1 4
#define ADDX_PIN_2 1
#define ADDX_PIN_3 2
#define ADDX_PIN_4 0
#define ADDX_PIN_MASK ((1 << ADDX_PIN_0) | (1 << ADDX_PIN_1) | (1 << ADDX_PIN_2) | (1 << ADDX_PIN_4))
SmartMatrix_Impl.h
I added this part:
#ifdef ADDX_PIN_4
if (i & 0x10) addressLUT[i].bits_to_set |= (1 << ADDX_PIN_4);
#endif
#ifndef ADDX_UPDATE_ON_DATA_PINS
int i;
// fill addressLUT
for (i = 0; i < matrixRowsPerFrame; i++) {
// set all bits that are 1 in address
addressLUT[i].bits_to_set = 0x00;
if (i & 0x01)
addressLUT[i].bits_to_set |= (1 << ADDX_PIN_0);
if (i & 0x02)
addressLUT[i].bits_to_set |= (1 << ADDX_PIN_1);
if (i & 0x04)
addressLUT[i].bits_to_set |= (1 << ADDX_PIN_2);
#ifdef ADDX_PIN_3
if (i & 0x08)
addressLUT[i].bits_to_set |= (1 << ADDX_PIN_3);
#endif
#ifdef ADDX_PIN_4
if (i & 0x10) addressLUT[i].bits_to_set |= (1 << ADDX_PIN_4);
#endif
// set all bits that are clear in address
addressLUT[i].bits_to_clear = (~addressLUT[i].bits_to_set) & ADDX_PIN_MASK;
}
#endifI’m having a hard time following everything you changed going from it working to not working.
When it “worked fine” is that after you “changed the code as described above”?
If you remove the second screen, and keep the code the same, does it work better (at least filling the first panel)?
Hi…I have a setup with teensy 3.6+ smartmatrixV4 running a 196x64 display…1/32 refresh rate. Is it possible to add another 196x64 display showing same content simultaneously from the same ribbon cable output from snartmatrix shield ? In short, can one snartmatrix shield can show same content from teensy on two displays side by side ?? Curious to know. Or what could be the best way to do something like that. If some one can share some ideas, highly appreciate. Thanks.
Most likely, you have problems if you directly connect two screens to the same output. The output cables should be as short as possible, and if you want to share the same output with several screens, the total length of the cable increases.
You could do this by adding a buffer with a pair of 74LS245 per screen, to isolate and amplify the signals on each screen.
I already tried this a long time ago and it worked well, in my case it was not to share an output with several screens, but to connect a relatively long cable, I think was about 60cm. Connected directly, the screen worked badly, the signals suffered many interferences, when I added the buffer with a pair of 74LS245 everything was solved.
I agree with @pinballsp, but it’s worth a try at least to see if you can wire up two screens without issues.
@marcmerlin drives two displays on his wearable LED screen setup with nearly identical content by feeding the output of one display into the other. The colors might be a bit off by doing this, but he can’t see the difference, and neither can I in the videos he’s shown this.
Yeah, I can confirm it just works, plug your last panel from the first set of displays into the first panel of the 2nd set.
The 2nd set will be one frame refresh behind, but at 100Hz+, you won’t be able to see it.
Only thing to keep in mind is to re-inject power. On a long run, I also had to re-inject ground to make sure ground was exactly the same on all panels (both across the data plug, which does send ground, but also the power plug)