# ModBus R41A08 relay board and Node-Red
<abstract>
This article explains how to manage the cheap Modbus 8 relay board R41A08 from Node-Red
</abstract>
<img src="./R41A08.jpg">
Nodes to install:
* node-red-contrib-modbus
<https://flows.nodered.org/node/node-red-contrib-modbus>
## Node-Red - Flow
[{"id":"34943ba9.6530b4","type":"modbus-flex-write","z":"71ad9872.edea58","name":"","showStatusActivities":false,"showErrors":false,"server":"9b45273.add55d8","x":930,"y":640,"wires":[[],[]]},{"id":"9d643725.bc6ae8","type":"function","z":"71ad9872.edea58","name":"8 relay board","func":"if (msg.payload[\"state\"]===0) {\n\n msg.payload={\n \"value\": 512,\n \"fc\": 6,\n \"unitid\": 1,\n \"address\": msg.payload[\"rele\"],\n \"quantity\": 1\n }\n} else {\n msg.payload={\n \"value\": 256,\n \"fc\": 6,\n \"unitid\": 1,\n \"address\": msg.payload[\"rele\"],\n \"quantity\": 1\n }\n}\n\nreturn msg;","outputs":1,"noerr":0,"x":750,"y":640,"wires":[["34943ba9.6530b4"]]},{"id":"2e1ee3fa.5d265c","type":"inject","z":"71ad9872.edea58","name":"RELAY 1 ON","topic":"","payload":"{\"rele\":1,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":280,"wires":[["9d643725.bc6ae8"]]},{"id":"bd4854e7.ac1ab8","type":"inject","z":"71ad9872.edea58","name":"RELAY 1 OFF","topic":"","payload":"{\"rele\":1,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":320,"wires":[["9d643725.bc6ae8"]]},{"id":"4ff31588.542ffc","type":"inject","z":"71ad9872.edea58","name":"RELAY 2 ON","topic":"","payload":"{\"rele\":2,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":380,"wires":[["9d643725.bc6ae8"]]},{"id":"cf77f1a.b5d181","type":"inject","z":"71ad9872.edea58","name":"RELAY 2 OFF","topic":"","payload":"{\"rele\":2,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":420,"wires":[["9d643725.bc6ae8"]]},{"id":"f710b9f5.e369a8","type":"inject","z":"71ad9872.edea58","name":"RELAY 3 ON","topic":"","payload":"{\"rele\":3,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":480,"wires":[["9d643725.bc6ae8"]]},{"id":"76ab0f31.b3eeb","type":"inject","z":"71ad9872.edea58","name":"RELAY 3 OFF","topic":"","payload":"{\"rele\":3,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":520,"wires":[["9d643725.bc6ae8"]]},{"id":"4fd45b86.0fec94","type":"inject","z":"71ad9872.edea58","name":"RELAY 4 ON","topic":"","payload":"{\"rele\":4,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":580,"wires":[["9d643725.bc6ae8"]]},{"id":"ad21c306.0ab48","type":"inject","z":"71ad9872.edea58","name":"RELAY 4 OFF","topic":"","payload":"{\"rele\":4,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":620,"wires":[["9d643725.bc6ae8"]]},{"id":"e3559ab4.db5498","type":"inject","z":"71ad9872.edea58","name":"RELAY 5 ON","topic":"","payload":"{\"rele\":5,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":680,"wires":[["9d643725.bc6ae8"]]},{"id":"d61acf97.53a6d","type":"inject","z":"71ad9872.edea58","name":"RELAY 5 OFF","topic":"","payload":"{\"rele\":5,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":720,"wires":[["9d643725.bc6ae8"]]},{"id":"fa394dd.203b7b","type":"inject","z":"71ad9872.edea58","name":"RELAY 6 ON","topic":"","payload":"{\"rele\":6,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":780,"wires":[["9d643725.bc6ae8"]]},{"id":"f57c8488.9971d8","type":"inject","z":"71ad9872.edea58","name":"RELAY 6 OFF","topic":"","payload":"{\"rele\":6,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":820,"wires":[["9d643725.bc6ae8"]]},{"id":"f0637366.4f4eb","type":"inject","z":"71ad9872.edea58","name":"RELAY 7 ON","topic":"","payload":"{\"rele\":7,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":880,"wires":[["9d643725.bc6ae8"]]},{"id":"b5dd9c0e.5b4ad","type":"inject","z":"71ad9872.edea58","name":"RELAY 7 OFF","topic":"","payload":"{\"rele\":7,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":920,"wires":[["9d643725.bc6ae8"]]},{"id":"41132eec.c808f","type":"inject","z":"71ad9872.edea58","name":"RELAY 8 ON","topic":"","payload":"{\"rele\":8,\"state\":1}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":980,"wires":[["9d643725.bc6ae8"]]},{"id":"b7c974ca.55b048","type":"inject","z":"71ad9872.edea58","name":"RELAY 8 OFF","topic":"","payload":"{\"rele\":8,\"state\":0}","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":130,"y":1020,"wires":[["9d643725.bc6ae8"]]},{"id":"34cc6e0a.6e3cd2","type":"inject","z":"71ad9872.edea58","name":"Go","topic":"","payload":"go","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":"2","x":390,"y":160,"wires":[["20543bb5.22ce44"]]},{"id":"f421fb69.0ef9a8","type":"function","z":"71ad9872.edea58","name":"Get rotate flag","func":"var relay = flow.get('relay');\nvar rotate = flow.get('rotate');\n\nnode.status({text:relay});\n\nif (rotate==1) {\n relay += 1;\n if (relay>8) { \n flow.set('relay',0);\n flow.set('rotate',0);\n return;\n } \n flow.set('relay',relay);\n} \nmsg.payload={\"rele\":relay,\"state\":1};\nreturn msg;","outputs":1,"noerr":0,"x":540,"y":200,"wires":[["9d643725.bc6ae8"]]},{"id":"20543bb5.22ce44","type":"function","z":"71ad9872.edea58","name":"Set rotate flag","func":"flow.set('rotate',1);\nflow.set('relay',0);\nreturn msg;","outputs":1,"noerr":0,"x":540,"y":160,"wires":[[]]},{"id":"e47a1b69.884f78","type":"inject","z":"71ad9872.edea58","name":"","topic":"","payload":"","payloadType":"date","repeat":"0.1","crontab":"","once":false,"onceDelay":"1","x":370,"y":200,"wires":[["f421fb69.0ef9a8"]]},{"id":"50f892fd.4d8a3c","type":"inject","z":"71ad9872.edea58","name":"Shutdown","topic":"","payload":"sudo shutdown","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":940,"y":160,"wires":[["cb8cab01.2b3be8"]]},{"id":"cb8cab01.2b3be8","type":"exec","z":"71ad9872.edea58","command":"","addpay":true,"append":"","useSpawn":"false","timer":"","oldrc":false,"name":"","x":1090,"y":160,"wires":[[],[],[]]},{"id":"9b45273.add55d8","type":"modbus-client","z":"","name":"","clienttype":"simpleser","bufferCommands":true,"stateLogEnabled":false,"tcpHost":"127.0.0.1","tcpPort":"502","tcpType":"DEFAULT","serialPort":"/dev/ttyUSB2","serialType":"RTU","serialBaudrate":"9600","serialDatabits":"8","serialStopbits":"1","serialParity":"none","serialConnectionDelay":"100","unit_id":1,"commandDelay":1,"clientTimeout":1000,"reconnectTimeout":2000}]
## Mini RS485 sniffer
In order to understand how to manage the Modbus protocol I've used this simple RS485 sniffer in Python
import serial
import time
port = '/dev/ttyUSB2'
baud = 9600
ser = serial.Serial(port, baud, timeout=0)
counter = 0
while True:
if ser.in_waiting>0:
c=ser.read(1)
print "%02X " % (ord(c)),
counter+=1
if counter==16:
print
counter=0
time.sleep(0.01)
## Raw data on RS485 bus
This is the sequence in hexadecimal of the bytes to send on RS485 bus at 9600,N,8,1
to the 8 relay board to turn on and turn off each relay
01 06 00 01 01 00 D9 9A 01 06 00 01 01 00 D9 9A
01 06 00 01 02 00 D9 6A 01 06 00 01 02 00 D9 6A
01 06 00 02 01 00 29 9A 01 06 00 02 01 00 29 9A
01 06 00 02 02 00 29 6A 01 06 00 02 02 00 29 6A
01 06 00 03 01 00 78 5A 01 06 00 03 01 00 78 5A
01 06 00 03 02 00 78 AA 01 06 00 03 02 00 78 AA
01 06 00 04 01 00 C9 9B 01 06 00 04 01 00 C9 9B
01 06 00 04 02 00 C9 6B 01 06 00 04 02 00 C9 6B
01 06 00 05 01 00 98 5B 01 06 00 05 01 00 98 5B
01 06 00 05 02 00 98 AB 01 06 00 05 02 00 98 AB
01 06 00 06 01 00 68 5B 01 06 00 06 01 00 68 5B
01 06 00 06 02 00 68 AB 01 06 00 06 02 00 68 AB
01 06 00 07 01 00 39 9B 01 06 00 07 01 00 39 9B
01 06 00 07 02 00 39 6B 01 06 00 07 02 00 39 6B
01 06 00 08 01 00 09 98 01 06 00 08 01 00 09 98
01 06 00 08 02 00 09 68 01 06 00 08 02 00 09 68
## Links
* [Python 8 Channel RS485 MODBUS RTU relay board type R421A08](https://github.com/Erriez/R421A08-rs485-8ch-relay-board)
@include='bio_sergio_tanzilli'
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