Same setup here. Do share the code please.
Here is the Node Red export that communicates with HA. You should be able to import directly into Node Red (I think)
[{“id”:“537ff01a.d5694”,“type”:“tab”,“label”:“Arcam Serial”,“disabled”:false,“info”:“”},{“id”:“44db0922d68e743c”,“type”:“serial in”,“z”:“537ff01a.d5694”,“name”:“Arcam”,“serial”:“9b6c3c03.9253f”,“x”:110,“y”:640,“wires”:[[“069ade71dffbeb06”,“7dfadfb3b9d2d04b”,“a886b1ec6801ec26”,“0e76b3690275815c”]]},{“id”:“f4409487.fa405”,“type”:“function”,“z”:“537ff01a.d5694”,“name”:“Convert volume to actual level”,“func”:“let data = […msg.payload]\ndata = data.map(hex => parseInt(hex));\ndata[6] = data[6] - 48; // or 0x30 or "0x30"\nmsg.payload = data;\nreturn msg;”,“outputs”:1,“noerr”:0,“initialize”:“”,“finalize”:“”,“libs”:,“x”:610,“y”:480,“wires”:[[“5a12ef2665f015c4”]]},{“id”:“5a12ef2665f015c4”,“type”:“ha-entity”,“z”:“537ff01a.d5694”,“name”:“Send volume to HA”,“server”:“cbd47e7957cb4d83”,“version”:2,“debugenabled”:false,“outputs”:1,“entityType”:“sensor”,“config”:[{“property”:“name”,“value”:“Volume”},{“property”:“device_class”,“value”:“”},{“property”:“icon”,“value”:“mdi:volume-equal”},{“property”:“unit_of_measurement”,“value”:“dB”},{“property”:“state_class”,“value”:“”},{“property”:“last_reset”,“value”:“”}],“state”:“payload[6]”,“stateType”:“msg”,“attributes”:,“resend”:true,“outputLocation”:“payload”,“outputLocationType”:“none”,“inputOverride”:“allow”,“outputOnStateChange”:false,“outputPayload”:“”,“outputPayloadType”:“str”,“x”:910,“y”:480,“wires”:[]},{“id”:“069ade71dffbeb06”,“type”:“switch”,“z”:“537ff01a.d5694”,“name”:“Check volume command”,“property”:“payload[3]”,“propertyType”:“msg”,“rules”:[{“t”:“eq”,“v”:“0x2f”,“vt”:“str”}],“checkall”:“true”,“repair”:false,“outputs”:1,“x”:290,“y”:480,“wires”:[[“f4409487.fa405”]]},{“id”:“a886b1ec6801ec26”,“type”:“switch”,“z”:“537ff01a.d5694”,“name”:“Check source input”,“property”:“payload[3]”,“propertyType”:“msg”,“rules”:[{“t”:“eq”,“v”:“0x31”,“vt”:“str”}],“checkall”:“true”,“repair”:false,“outputs”:1,“x”:310,“y”:680,“wires”:[[“1f89e1860f9973da”]]},{“id”:“7dfadfb3b9d2d04b”,“type”:“switch”,“z”:“537ff01a.d5694”,“name”:“Check display”,“property”:“payload[3]”,“propertyType”:“msg”,“rules”:[{“t”:“eq”,“v”:“0x2b”,“vt”:“str”}],“checkall”:“true”,“repair”:false,“outputs”:1,“x”:320,“y”:600,“wires”:[[“e882bdf78af02669”]]},{“id”:“0b7236e323df4bdb”,“type”:“switch”,“z”:“537ff01a.d5694”,“name”:“Check analogue or digital”,“property”:“payload[4]”,“propertyType”:“msg”,“rules”:[{“t”:“eq”,“v”:“55”,“vt”:“num”}],“checkall”:“true”,“repair”:false,“outputs”:1,“x”:310,“y”:760,“wires”:[]},{“id”:“e882bdf78af02669”,“type”:“ha-entity”,“z”:“537ff01a.d5694”,“name”:“Send display value to HA”,“server”:“cbd47e7957cb4d83”,“version”:2,“debugenabled”:true,“outputs”:1,“entityType”:“sensor”,“config”:[{“property”:“name”,“value”:“Arcam Display”},{“property”:“device_class”,“value”:“”},{“property”:“icon”,“value”:“”},{“property”:“unit_of_measurement”,“value”:“”},{“property”:“state_class”,“value”:“”},{“property”:“last_reset”,“value”:“”}],“state”:“payload[6]”,“stateType”:“msg”,“attributes”:,“resend”:true,“outputLocation”:“payload”,“outputLocationType”:“none”,“inputOverride”:“allow”,“outputOnStateChange”:false,“outputPayload”:“”,“outputPayloadType”:“str”,“x”:930,“y”:580,“wires”:[]},{“id”:“1f89e1860f9973da”,“type”:“ha-entity”,“z”:“537ff01a.d5694”,“name”:“Send input to HA”,“server”:“cbd47e7957cb4d83”,“version”:2,“debugenabled”:false,“outputs”:1,“entityType”:“sensor”,“config”:[{“property”:“name”,“value”:“Arcam Input”},{“property”:“device_class”,“value”:“”},{“property”:“icon”,“value”:“”},{“property”:“unit_of_measurement”,“value”:“”},{“property”:“state_class”,“value”:“”},{“property”:“last_reset”,“value”:“”}],“state”:“payload[6]”,“stateType”:“msg”,“attributes”:,“resend”:true,“outputLocation”:“payload”,“outputLocationType”:“none”,“inputOverride”:“allow”,“outputOnStateChange”:false,“outputPayload”:“”,“outputPayloadType”:“str”,“x”:910,“y”:680,“wires”:[]},{“id”:“0e76b3690275815c”,“type”:“switch”,“z”:“537ff01a.d5694”,“name”:“Check volume change command”,“property”:“payload[3]”,“propertyType”:“msg”,“rules”:[{“t”:“eq”,“v”:“0x30”,“vt”:“str”}],“checkall”:“true”,“repair”:false,“outputs”:1,“x”:320,“y”:540,“wires”:[[“f4409487.fa405”]]},{“id”:“9b6c3c03.9253f”,“type”:“serial-port”,“serialport”:“/dev/serial/by-id/usb-FTDI_FT232R_USB_UART_00000000-if00-port0”,“serialbaud”:“38400”,“databits”:“8”,“parity”:“none”,“stopbits”:“1”,“waitfor”:“”,“dtr”:“none”,“rts”:“none”,“cts”:“none”,“dsr”:“none”,“newline”:“0xd”,“bin”:“bin”,“out”:“char”,“addchar”:“”,“responsetimeout”:“10000”},{“id”:“cbd47e7957cb4d83”,“type”:“server”,“name”:“Home Assistant”,“version”:2,“addon”:true,“rejectUnauthorizedCerts”:true,“ha_boolean”:“y|yes|true|on|home|open”,“connectionDelay”:true,“cacheJson”:true,“heartbeat”:false,“heartbeatInterval”:“30”}]