This driver controls chinese RGB LED Matrix modules without any additional components whatsoever. These panels are commonly used in large-scale LED displays and come in diffent layouts and resolutions (32x16, 32x32, 64x32, 64x64), e.g. see aliexpress. The driver is Adafruit GFX compatible and currently works with ESP8266 microcontrollers. However, it should be rather straightforward to port it to ESP32 or Atmel-based Arduinos.
The display basically consists of 6 large shift register. On the input connector you will find the inputs to the shift register (two for each color - Rx,Gx,Bx), a 2 to 4 bit latch address input (A,B,C,D), a latch enable input (LAT/STB), a clock input (CLK) and the output enable input (OE).
There are a few basic layouts/patterns: 4 row-step (4RS), 8 row-step (8RS), 16 row-step (16RS) or 32 row-step (32RS). You can enable the correct pattern for your display with display.begin(n) where n={4,8,16,32} defines the pattern.
For example, the 32x16 displays work like this (other varieties operate accordingly): Each of the shift register is 64(4RS)/32(8RS) bits long. R1 and R2 will together therefore cover 128(4RS)/64(8RS) bits or 4(4RS)/2(8RS) lines respectively. The rows are, however, not next to each other but have a spacing of 4(4RS)/8(8RS). In case of 4RS adjacent bytes also alternate between lines n and n+4.
Setting Rx to high, cycling CLK 64(4RS)/32(8RS) times, setting (A,B,C) to low and setting LAT/STB to low will light up rows 0,4,8,12(4RS)/0,8(8RS). Repeating the same experiment with A high, B and C low will light up rows 1,5,8,13(4RS)/1,9(8RS) and so forth. The same principle applies to the other colors. As the row spacing for 4RS is 4 we only need A and B for the latch address - C has no function. 8RS requires a C, 16RS requires a D and 32RS requires an E signal.
Such LED matrix are usually used as a sub-module for larger displays and therefore features an output connector for daisy chaining. On the output connector you will find the identical signals to the input connector where A,B,C,LAT,CLK are simply routed through and (R,G,B) pins are the outputs of the shift registers on the module.
When driving a long chain of LED modules in a row, parallel color data lines make a lot of sense since it reduces the data rate. But since we are only driving a single module here, we really don't need that. We can therefore use jumper wires between input connector (PI) and output connector (PO) to chain all shift registers together and create one big shift register. This has two advantages: it reduces the number of required GPIO pins on the microcontroller and we can use the hardware SPI interface to drive it.
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If your panel input connector has "R1" in the top left corner:
Connect PI and PO as follows:
PI PO R2 R1 G1 R2 G2 G1 B1 G2 B2 B1 Connect panel input (PI) to the NodeMCU/ESP8266 (ESP) as follows:
PI ESP STB/LAT 16 - (D0) A 05 - (D1) B 04 - (D2) C 15 - (D8) (only for 8RS, 16RS, 32RS) D 12 - (D6) (only for 16RS, 32RS) E 00 - (D3) (only for 32RS) P_OE 02 - (D4) CLK 14 - (D5) R1 13 - (D7) -
If your panel input connector has "R0" in the top left corner:
Connect PI and PO as follows:
PI PO R1 R0 G0 R1 G1 G0 B0 G1 B1 B0 Connect panel input (PI) to the NodeMCU/ESP8266 (ESP) as follows:
PI ESP STB/LAT 16 - (D0) A 05 - (D1) B 04 - (D2) C 15 - (D8) (only for 8RS, 16RS, 32RS) D 12 - (D6) (only for 16RS, 32RS) E 00 - (D3) (only for 32RS) P_OE 02 - (D4) CLK 14 - (D5) R0 13 - (D7)
You should end up with something like this (VCC/supply not nonnected here yet):
The number of color levels can be selected in the header file. The default (8 color levels per primary RGB color) works well with hardly any flickering. Note that the number of color levels determines the achievable display refresh rate. Hence, the more color levels are selected, the more flickering is to be expected. If you run into problems with flickering it is a good idea to increase the CPU frequency to 160MHz. This way the processor has more headroom to compute the display updates and refresh the display in time.
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Check you cabling with a multimeter (diode-test). You can measure the connection between the input/ouput panel connector and the NodeMCU/ESP8266 via the exposed SMD pads/legs.
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Your display may have a different scanning pattern. Make sure that you have selected the correct scanning pattern in the display.begin call
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Run the "P10_pattern_test.ino" and check if the scanning pattern is appearing ok. For a 8 row-step display it should look like this (red then yellow then white line progressing):
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It is possible that the LED multiplex chip is defective (this was the case with one of my modules). You can verify this by selecting a bit pattern on the A,B,C inputs and measuring that the corresponing row outputs are low , e.g. a 4 row-step display typically uses a (PR4538) chip. Setting (A=1,B=0) should give you (LINE0=1,LINE1=0,LINE2=1,LINE3=1). This chip can easily be replaced. Spare part available here.
Test sketch with 16 levels per primary color
Animated weather clock from here
Animated picture frame from here
Pixels from eboy