Hi, I have problems to convert float and 32b (signed/unsigned) registers to obtain a result able to be sent to MQTT broker. The modbus device is a semaphore/Servelec Tbox unit. I use node-red modbustcp Example: I have a float register with a value of 22.362 in it. I want to pass that value to my MQTT broker. When I debug in node-red, I obtain an array: [16818,58720] but I'm stuck to convert this to a readable precise value of 22.362 (22.36 will be ok) I have no probs with int16 registers (because they are 16bits obviously but need to find a function to convert negative values to readable ones) I found here a function but the result seems weird (imprecise). *Edit: I made my test simple. That's the reason I set the value of 22.362 into register 22362 ! Easier to remember [NodeRed - float to value]

In the Change nodes where you extract the individual parts add another row that Sets msg.topic To the/topic/for/this/value

[image] Steve-Mcl: I suspect when you update msg.payload in function 1 you are affecting the object before it's processed in the 2nd function. Assuming this is in a recent version of node-red (@PPz which version is it?) then I don't think that should happen as node-red should automatically clone the message for the second wire out of the node. @PPz in the functions use node.warn() to show the contents of pay after you have picked it up.

[image] Colin: node.warn() thank you both of you (@Steve-Mcl) for your kind help. My version is 1.0.3 the code of the function is : let pay = msg.payload; const buf = Buffer.allocUnsafe(4); // (4) is ok buf.writeUInt16BE(pay[0]); // high byte msg.payload = buf.readFloatBE(0); // 2 numbers after comma (string) // msg.payload = buf.readFloatBE(0).toFixed(2); // return msg; the float value into my plc is 22.362 the raw received data is an array [16818,58720] the result (after function) varies from 22.25 to 22.37 about node.warn(), I'm affraid that I'm a real newbie about node-red

[image] PPz: about node.warn(), I'm affraid that I'm a real newbie about node-red Have you tried searching for it?

[image] Colin: node.warn() Yes, but when I inject node.warn(pay); I receive exactly the same array value [16818,58720] as the raw debug message Update: when I inject node.warn(buf), I obtain a splitted array like this one: [65,178,98,5], or [65,178,125,3], or [65,178,0,0] (variable). Ok, 16818 = (256*65)+178 Update 2: for what I understand here, the 2 first values of the array [65,178] seems consistent and represent probably/certainly the value that doesn't change (22). Why the others are changing ? A real mystery for me. Update 3: maybe it will help you, but the weird thing about my plc is that the right value is in the array when dealing with 32b registers. If I poll a 32b register with a value of 22358, the node-red poll send me an array with [0,22358]. So it seems that's even not a hex value, just the plain decimal value...

[image] PPz: let pay = msg.payload; const buf = Buffer.allocUnsafe(4); // (4) is ok buf.writeUInt16BE(pay[0]); // high byte msg.payload = buf.readFloatBE(0); You are allocating a buffer of length 4 bytes. Then you use writeUInt16BE to write to the first two bytes. You have not written anything to the second two bytes so they are left with whatever happened to be lying around in that bit of memory. That is why they contain variable data. You then use readFloat to read all four bytes to give you the (veriable) result.

[image] Payload's number to two 16 bit register to be send via modbus General Hi ! U can use this code in function....after connect it to Modbus Flex Write function float32ToUint16(value) { var buffer = new ArrayBuffer(4); var intView = new Uint16Array(buffer); var floatView = new Float32Array(buffer); floatView[0] = value; return [intView[0], intView[1]]; } //var incoming = JSON.parse(msg.payload); //Compose ModBus message (Holding Registers) READ/WRITE var modbusHR = { payload : { 'value' : [ float32ToUint16(msg.payload)[0], float32ToUint16(msg.…

tagging @Iqapps Thank you. I need to dig more about this and I will probably come come back later with this. For you, it's probably a piece of cake. Not that obvious for me (must read some doc. I usually learn while have a problem to solve). For the moment, I simplified my problem with my PLC (that I know far better): I created a bunch of 16b variables and made a small pgm (into my plc) to convert some floats registers into int16 (float*100) and I transform them into floats (int16/100) to obtain a nice result with node-red and passing the values to mqtt and hubitat [shame on me). Because my main problem was to harvest modbus data and send them to Hubitat. Learn Hubitat, MQTT apps, mosquitto and Node-red at the same time is a little bit too much for me (I'm an old guy). Thank you again for your answers. Mike [modbus-node-red-mqtt-hubitat]

Here is little more information about how modbus handle 32 bit.... [image] How Real (Floating Point) and 32-bit Data is Encoded in Modbus RTU Messages Modbus Integration Solutions Chipkin has Modbus solutions for almost every situation. We are experts in Modbus RTU/TCP communication and carry a wide variety of Modbus products: ...

tagging @Colin thanks for the doc and the help. I discovered more and more and simplified a lot. Build on my plc a set of int16 registers. at first, I defined different polls, but the target plc was not happy of that (poll errors) Like in modbus devices, I set now 1 poll with successive addresses :slight_smile: Far better ! But now, with that method, I loose my different topic names for my MQTT broker (before: 1 topic per poll, now: 1 topic only because 1 poll) Is it a way to define an array of topics when polling once and/or functions to build a specific topic for each extracted value ? Before: [multiple reads] After: [1 multiple read]

Mucho Perfecto ! And much faster too... [nore-red 1 poll multiple topics mqtt] [hubitat-mqtt-modbus]

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Newbie: convert modbus float [array] register to float value

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Iqapps 15 January 2020 10:39 11

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Newbie: convert modbus float [array] register to float value

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