LED 7 Segment Display, MODBUS-RTU Display Module, 4 Digits Display with RS485 Serial Port for PLC Communication (5-36V)

worked great

No documentation. imposible to set it up.

The functionality and price of this product are excellent. Unfortunately, as others have noted, it is very difficult to find any technical information (e.g., no manual, no customer support, etc.). Thanks to other reviews here and elsewhere I was able to piece together enough information to use it (e.g., default node/slave ID is 1, baud rate is 9600, write to holding register 0 to set the number 0-9999 to be displayed). However, the information was not complete or entirely correct, so I am adding my notes also:* Register mapping:0: number to be displayed: values 0-9999 map to 0000 to 9999, as expected. -1 to -999 can be displayed as well (2's complement, e.g., 64537 = -999). For positive values there are leading zeros, for negative ones the minus sign appears on the left then blanks are padded until the first non-zero digit. While I didn't find a proper way to disable leading zeros, I did notice that sending 20000 to 20999 displays _000 to _999 (one leading zero suppressed, though I suspect it is a glitch / accident / coincidence.1: Decimal point position (0 for none, 1 for XXX.X, ... did not test much) -- stored [persists after power loss]2: Brightness -- stored [persists after power loss]3-5: unknown function6: Setting to 0 causes blinking; setting 256 causes steady (non-blinking) illumination stored [persists after power loss]7: Baud rate 0-7 (1200, ..., 115200)8: Slave/Node ID 0-255 (did not try setting the high byte in the register to anything other than 0)9-255: unknown* Registers appear to "wrap around" after 255, e.g., setting "register 256" is equivalent to setting "register 0"* When the device is first powered-on it will display its node/slave ID using the first (left-most) digits and its baud rate code using the last (right-most) digit. e.g., 2557 means node 255/0xFF using baud rate code 7 for 115200 bps.* Device uses STC8G1K08 microcontroller and TM1650 segment driver

Scoured the web for a manual for this thing but had no luck. Eventually figured it out so I thought I'd share for everyone else on here:You have to use the corresponding modbus holding registers to assign the parameters listed in the directions.register 1 is for the data bits. These are the values that will appear on the displayregister 2 is for the decimal position. 00= XXXX, 01= XXX.X, 02= XX.XX, 03= X.XXXregister 3 is for the brightness. 00 is the dimmest and 07 is the brightestregister 4 is for the baud rate. 00 = 1200, 01 = 2400, 02 = 4800, 03 = 9600,. etc..Hopefully this will save you some time.Here is a sample of the code I used to test it out:#include <ModbusMaster.h>// Modbus slave ID#define SLAVE_ID 1// Number of registers to send#define NUM_REGISTERS 4// Modbus address for each register (1-4)#define REGISTER_1 0x0000#define REGISTER_2 0x0001#define REGISTER_3 0x0002#define REGISTER_4 0x0003#define RS485SerialTxPin 6#define RS485SerialRxPin 7// Define the array to store data for each registeruint16_t holdingRegs[NUM_REGISTERS];// Modbus objectModbusMaster node;void setup() {Serial.begin(9600); // Start the serial communicationnode.begin(SLAVE_ID, Serial);// Initialize the holding registersholdingRegs[REGISTER_1] = 05; //data bitholdingRegs[REGISTER_2] = 01; //decimal positionholdingRegs[REGISTER_3] = 07; //brightnessholdingRegs[REGISTER_4] = 03; //baudrate}void loop() {// Update the data in the holding registersholdingRegs[REGISTER_1] = 05;holdingRegs[REGISTER_2] = 01;holdingRegs[REGISTER_3] = 07;holdingRegs[REGISTER_4] = 03;// Send the holding register data to Modbus registersfor (int i = 0; i < NUM_REGISTERS; i++) {node.writeSingleRegister(i, holdingRegs[i]);delay(10); // Add a short delay to prevent communication issues}// Your additional code can go here}

Item arrived with no documentation whatsoever. Product listing has insufficient information.back it goes.

I was stuck in a dead end using this until other reviews provided test code. My particular test involved using different tx and rx pins for my breakout board on an arduino but the display now works great.