Has anybody experience with MODBUS to read temp sensors?

[Rudy M]

@Petr:
Thank you for the detailed technical information. 
Sorry for the late reply,
but I'll try to fully review the data tips today and will compile a summary of the results.

Rudy M

[Rudy M]

Hi Petr,

Testing with Your tips concerning the Linux commands I saw no ttyUSB0 but ttyASM0

(Search via Google "ttyUSB0 ttyASM0" gives a lot of links)

So I did a test and in Your two last listings I changed the ttyUSB0 by ttyASM0

And thereafter both listings gave NOT anymore the the two errors: "File not found" or "Wrong slave adress".

I toke a print screen of both responces of Your Listings:









I did a simple third test: I disconnected the USB connector from my PC (==> error 'File not found')

Your last two programs running without errors give me hope that things will work out.
I hope we're on the right track now.

Greetings,
Rudy M

[Petr]

Rudy M, what RX led do? Blink or not?

[Rudy M]

Hi Petr,

Hi Petr, 

In Your second-to-last program, only the TXD LED lights up.
In Your last program, both the TXD and RXD LEDs light up.

(For a test I switched A and B, but that gives no result).

Rudy M

[Petr]

Hi, Rudy M, try this:

Code: (Select All)

OPTION _EXPLICIT





' PTA8D08 MODBUS RTU - Linux Mint - QB64PE

'

' IMPORTANT:

' - When opening /dev/ttyACM0 (or ttyUSB0) as a file, DO NOT use LOC()/GET

'  to decide if data is available. LOC() is not a RX-buffer indicator for files. :contentReference[oaicite:5]{index=5}

' - Use stty to set non-blocking-ish reads (min 0 time 1) and read via INPUT$.

'

' What this program does:

' 1) stty config: 9600 8N1 raw, no flow control, clocal, cread, min 0 time 1

' 2) TX: broadcast read 0x00FD (address/DIP) - protocol gives example FF 03 00 FD 00 01 00 24 :contentReference[oaicite:6]{index=6}

' 3) RX: dump any received bytes + try to extract a valid MODBUS frame by CRC

' 4) TX: read CH0 temperature (0x0000, count=1) - protocol example exists :contentReference[oaicite:7]{index=7}

'

' SEND FOR TUNING:

' - Which device path you used (prefer /dev/serial/by-id/...)

' - Confirm module is powered DC 8..30V on VIN/GND :contentReference[oaicite:8]{index=8}

' - Whether swapping A/B changes anything

' - The printed TX/RX hex dumps below

'===========================================================



DECLARE FUNCTION Crc16Modbus& (s$)

DECLARE FUNCTION U16BE$ (v&)

DECLARE FUNCTION HexDump$ (s$)

DECLARE FUNCTION ModbusBuildRead$ (slave%, reg&, count%)

DECLARE FUNCTION ModbusCheckCrc% (frame$)

DECLARE FUNCTION TryExtractFrame03$ (buf$, expectedSlave%)

DECLARE FUNCTION GetU16BE& (s$, position%)

DECLARE FUNCTION GetS16BE% (s$, position%)



DECLARE SUB SerialWrite (h%, s$)

DECLARE FUNCTION SerialReadSome$ (h%, timeoutSec!)

DECLARE SUB SleepMs (ms!)



DIM SHARED Byte1 AS STRING * 1



'========================

' MAIN (must be first)

'========================



DIM dev$        : dev$ = "/dev/ttyACM0"  ' your current device; /dev/ttyUSB0 is also common

DIM showFrames%  : showFrames% = -1

DIM timeout!    : timeout! = 1.0



DIM h%          : h% = FREEFILE

DIM cmd$

DIM req$, rxRaw$, frame$

DIM slave%      : slave% = 1



DIM dipOrAddr&

DIM rawTemp%

DIM tempC!



' 1) Configure port using stty

' - clocal: ignore modem control lines (important on many USB serial devices)

' - cread : enable receiver

' - min 0 time 1: read returns quickly even if no bytes are available (tenths of seconds)

cmd$ = "stty -F " + dev$ + " 9600 cs8 -cstopb -parenb -ixon -ixoff -crtscts raw -echo clocal cread min 0 time 1"

SHELL cmd$



' 2) Open the device as a binary file (byte-accurate)

OPEN dev$ FOR BINARY AS #h% LEN = 1



PRINT "Opened "; dev$; " (USB-Serial/RS485). ESC exits."

PRINT



'------------------------------------------------------------

' STEP A: Broadcast read 0x00FD (address / DIP settings)

' Protocol example: FF 03 00 FD 00 01 00 24 :contentReference[oaicite:9]{index=9}

'------------------------------------------------------------

req$ = ModbusBuildRead$(255, &H00FD, 1)

IF showFrames% THEN PRINT "TX addr (FF 00FD): "; HexDump$(req$)

SerialWrite h%, req$



rxRaw$ = SerialReadSome$(h%, timeout!)

IF showFrames% THEN PRINT "RX raw addr:      "; HexDump$(rxRaw$)



frame$ = TryExtractFrame03$(rxRaw$, 0) ' 0 = accept any slave in reply

IF LEN(frame$) = 0 THEN

    PRINT

    PRINT "No valid MODBUS frame received for 00FD."

    PRINT "This is NOT a software victory yet."

    PRINT "Focus on: module power (VIN DC 8..30V), A/B swap, GND reference, correct device path."  ' :contentReference[oaicite:10]{index=10}

    PRINT

ELSE

    PRINT "RX frame addr:    "; HexDump$(frame$)

    dipOrAddr& = GetU16BE&(frame$, 4)

    slave% = ASC(frame$, 1) AND &HFF

    PRINT "Station address from reply ="; slave%; "  (00FD raw data = &H"; HEX$(dipOrAddr&); ")"

    PRINT

END IF



'------------------------------------------------------------

' STEP B: Read CH0 temperature only (simpler than 8 regs while debugging)

' Protocol example for CH0 exists :contentReference[oaicite:11]{index=11}

'------------------------------------------------------------

req$ = ModbusBuildRead$(slave%, &H0000, 1)

IF showFrames% THEN PRINT "TX temp CH0:      "; HexDump$(req$)

SerialWrite h%, req$



rxRaw$ = SerialReadSome$(h%, timeout!)

IF showFrames% THEN PRINT "RX raw temp:      "; HexDump$(rxRaw$)



frame$ = TryExtractFrame03$(rxRaw$, slave%)

IF LEN(frame$) = 0 THEN

    PRINT

    PRINT "No valid MODBUS temp frame received."

    PRINT "If RX LED never blinks, it is wiring/power/address, not register mapping."

    PRINT

ELSE

    PRINT "RX frame temp:    "; HexDump$(frame$)

    ' frame: [addr][03][02][dataHi][dataLo][crcLo][crcHi]

    rawTemp% = GetS16BE%(frame$, 4)

    tempC! = rawTemp% / 10!

    PRINT "CH0 temperature ="; tempC!; "C"

    PRINT

    PRINT "If this works, switch to reading 8 regs: reg=0000 count=8 and parse 16 bytes."

END IF



PRINT

PRINT "Press ESC to exit."



DO

    IF INKEY$ = CHR$(27) THEN EXIT DO

    SleepMs 50

LOOP



CLOSE #h%

END



'========================

' SUBs / FUNCTIONs (must be last)

'========================



FUNCTION Crc16Modbus& (s$)

    DIM crc&, i%, j%

    crc& = &HFFFF&

    FOR i% = 1 TO LEN(s$)

        crc& = crc& XOR ASC(s$, i%)

        FOR j% = 1 TO 8

            IF (crc& AND 1) THEN

                crc& = (crc& \ 2) XOR &HA001&

            ELSE

                crc& = crc& \ 2

            END IF

        NEXT j%

    NEXT i%

    Crc16Modbus& = (crc& AND &HFFFF&)

END FUNCTION



FUNCTION U16BE$ (v&)

    U16BE$ = CHR$((v& \ 256) AND &HFF) + CHR$(v& AND &HFF)

END FUNCTION



FUNCTION HexDump$ (s$)

    DIM i%, out$

    out$ = ""

    FOR i% = 1 TO LEN(s$)

        out$ = out$ + RIGHT$("0" + HEX$(ASC(s$, i%)), 2) + " "

    NEXT i%

    HexDump$ = out$

END FUNCTION



FUNCTION ModbusBuildRead$ (slave%, reg&, count%)

    DIM req$, crc&

    req$ = CHR$(slave% AND &HFF) + CHR$(&H03) + U16BE$(reg&) + U16BE$(count%)

    crc& = Crc16Modbus&(req$)

    req$ = req$ + CHR$(crc& AND &HFF) + CHR$((crc& \ 256) AND &HFF)

    ModbusBuildRead$ = req$

END FUNCTION



FUNCTION ModbusCheckCrc% (frame$)

    DIM n%, crcRx&, crcCalc&

    n% = LEN(frame$)

    IF n% < 5 THEN ModbusCheckCrc% = 0: EXIT FUNCTION

    crcRx& = ASC(frame$, n% - 1) + 256& * ASC(frame$, n%)

    crcCalc& = Crc16Modbus&(LEFT$(frame$, n% - 2))

    ModbusCheckCrc% = (crcRx& = crcCalc&)

END FUNCTION



FUNCTION GetU16BE& (s$, position%)

    DIM hi&, lo&

    hi& = ASC(s$, position%) AND &HFF

    lo& = ASC(s$, position% + 1) AND &HFF

    GetU16BE& = hi& * 256& + lo&

END FUNCTION



FUNCTION GetS16BE% (s$, position%)

    DIM v&

    v& = GetU16BE&(s$, position%)

    IF v& >= 32768& THEN v& = v& - 65536&

    GetS16BE% = v&

END FUNCTION



SUB SerialWrite (h%, s$)

    DIM i%

    FOR i% = 1 TO LEN(s$)

        Byte1 = MID$(s$, i%, 1)

        PUT #h%, , Byte1

    NEXT i%

END SUB



FUNCTION SerialReadSome$ (h%, timeoutSec!)

    ' Read whatever arrives within timeoutSec!

    ' Uses INPUT$(1,#) repeatedly; with stty "min 0 time 1" it should not block forever.

    DIM t0!, b$, r$

    t0! = TIMER

    r$ = ""

    DO

        b$ = INPUT$(1, #h%)

        IF LEN(b$) > 0 THEN

            r$ = r$ + b$

        ELSE

            SleepMs 10

        END IF

        IF (TIMER - t0!) >= timeoutSec! THEN EXIT DO

        IF LEN(r$) > 512 THEN EXIT DO

    LOOP

    SerialReadSome$ = r$

END FUNCTION



FUNCTION TryExtractFrame03$ (buf$, expectedSlave%)

    ' Scan buffer for a valid MODBUS function 03 frame by CRC.

    ' expectedSlave% = 0 => accept any slave

    DIM i%, n%, addr%, fn%, bc%, frameLen%

    DIM candidate$



    n% = LEN(buf$)

    TryExtractFrame03$ = ""

    IF n% < 5 THEN EXIT FUNCTION



    FOR i% = 1 TO n% - 4

        addr% = ASC(buf$, i%) AND &HFF

        IF expectedSlave% <> 0 THEN

            IF addr% <> (expectedSlave% AND &HFF) THEN GOTO NextI

        END IF



        fn% = ASC(buf$, i% + 1) AND &HFF

        IF fn% <> &H03 THEN GOTO NextI



        bc% = ASC(buf$, i% + 2) AND &HFF

        frameLen% = 5 + bc%

        IF (i% + frameLen% - 1) <= n% THEN

            candidate$ = MID$(buf$, i%, frameLen%)

            IF ModbusCheckCrc%(candidate$) THEN

                TryExtractFrame03$ = candidate$

                EXIT FUNCTION

            END IF

        END IF



NextI:

    NEXT i%

END FUNCTION



SUB SleepMs (ms!)

    ' crude, portable sleep (milliseconds)

    _DELAY ms! / 1000!

END SUB

please write me back what program wrote about RX raw addr: and RX raw temp. 

Then try this version - its newerest.

Attention: "RX and TX LEDs are on" does not mean that the module is responding with the correct MODBUS data. With many RS-485 dongles, the RX LED flashes even when the transmitter is on (there is activity on the bus and the LED interprets it as RX). The only real proof is that the program prints a non-zero RX frame and passes the CRC.

Code: (Select All)

Option _Explicit



' PTA8D08 (8x PT100) - MODBUS RTU over RS-485 - Linux Mint

' QB64PE Linux-friendly implementation

'

' WHY THIS VERSION EXISTS:

' On Linux when opening /dev/ttyUSBx or /dev/ttyACMx as a file,

' using LOC(#)/GET to "poll RX bytes" is often unreliable.

' This version uses:

'  - stty to configure serial port (9600 8N1, raw, no flow control)

'  - non-blocking-ish behavior (min 0 time 1) so reads return quickly

'  - INPUT$(1,#) to read bytes into a buffer

'  - CRC-based extraction of MODBUS function 03 frames from that buffer

'

' DEVICE DEFAULTS (per vendor docs):

' - 9600, N, 8, 1

' - Function 03 = read holding registers

' - Temperatures: regs 0x0000..0x0007, signed, unit 0.1°C

' - Address/DIP info: read reg 0x00FD (broadcast request allowed)

'

' IMPORTANT HARDWARE NOTES:

' - The PTA8D08 board must be powered via VIN+GND (8..30V DC). RS-485 does NOT power it.

' - A/B labeling is inconsistent across vendors; if no reply, swap A and B.

' - Connecting adapter GND to module GND often improves reliability (reference).





Dim Shared Byte1 As String * 1





'User-configurable settings (edit these)

Dim dev$: dev$ = "/dev/ttyUSB0"

' TIP: Prefer a stable path like /dev/serial/by-id/.... if available.



Dim pollHz!: pollHz! = 2

Dim showFrames%: showFrames% = -1

Dim timeout!: timeout! = 1.0





Dim h%: h% = FreeFile

Dim cmd$

Dim req$, resp$

Dim slave%: slave% = 1

Dim i%

Dim rawS%

Dim t!

Dim dipRaw&

Dim key$





' What to send back for debugging

Print "============================================================"

Print "PTA8D08 MODBUS RTU tester (Linux, QB64PE)"

Print

Print "DEBUG INFO TO SEND BACK (copy/paste output):"

Print "1) ls -l /dev/serial/by-id/"

Print "2) ls -l /dev/ttyUSB* /dev/ttyACM*"

Print "3) groups"

Print "4) lsof "; dev$

Print "5) Confirm module power: VIN = 8..30V DC (and wiring photo if possible)."

Print "6) Confirm whether swapping A/B changes behavior."

Print "7) Paste TX/RX hex dumps printed by this program."

Print "============================================================"

Print







' Configure serial port via stty

'----------------------------------------------------------------

' Explanation:

' - raw:        disable canonical processing, special chars, etc.

' - -echo:      no echo

' - -ixon/-ixoff: disable software flow control

' - -crtscts:  disable hardware flow control

' - clocal:    ignore modem control lines (important on USB serial)

' - cread:      enable receiver

' - min 0 time 1: read returns quickly even if no bytes are available (0.1s units)

cmd$ = "stty -F " + dev$ + " 9600 cs8 -cstopb -parenb -ixon -ixoff -crtscts raw -echo clocal cread min 0 time 1"

Shell cmd$





' Open the device as a binary file

' LEN=1 ensures PUT/GET operate on single bytes correctly.



Open dev$ For Binary As #h% Len = 1



Print "Opened "; dev$; " (USB-RS485). Press ESC to exit."

Print





' STEP 0: Broadcast read 0x00FD to discover station address/DIP.

' Request (example from docs): FF 03 00 FD 00 01 00 24

' We build it dynamically using CRC.

'

' expectedSlave = 0 means: accept any slave address in the reply.



SerialFlush h%



req$ = ModbusBuildRead$(255, &H00FD, 1)

If showFrames% Then Print "TX addr (FF 00FD): "; HexDump$(req$)

SerialWrite h%, req$



resp$ = SerialReadFrame03$(h%, 0, timeout!)

If showFrames% Then Print "RX addr:          "; HexDump$(resp$)



If Len(resp$) > 0 And ModbusCheckCrc%(resp$) Then

    slave% = Asc(resp$, 1) And &HFF

    dipRaw& = GetU16BE&(resp$, 4)

    Print "Detected station address from reply ="; slave%

    Print "00FD raw register value (hex) = &H"; Hex$(dipRaw&)

    Print

Else

    Print "Could not read station address (00FD)."

    Print "This usually means: no real MODBUS reply is arriving."

    Print "Focus on: VIN power, A/B wiring swap, GND reference, correct device path, permissions."

    Print "Continuing with slave address ="; slave%; "(default)."

    Print

End If





' MAIN POLL LOOP: Read 8 temperatures (0x0000..0x0007) repeatedly

' Response for 8 regs should contain:

' [addr][03][16][16 data bytes][crcLo][crcHi]



Do

    key$ = InKey$

    If key$ = Chr$(27) Then Exit Do



    SerialFlush h%



    req$ = ModbusBuildRead$(slave%, &H0000, 8)

    If showFrames% Then Print "TX temps:          "; HexDump$(req$)

    SerialWrite h%, req$



    resp$ = SerialReadFrame03$(h%, slave%, timeout!)

    If showFrames% Then Print "RX temps:          "; HexDump$(resp$)



    If Len(resp$) = 0 Then

        Print "No MODBUS reply (temps)."

        Print "If RX LED never blinks: hardware/power/wiring/address is wrong."

        Print "If RX LED blinks but no frame: still likely wiring/power, or your adapter echoes/garbles data."

        Print

        _Limit pollHz!

        GoTo ContinueLoop

    End If



    If ModbusCheckCrc%(resp$) = 0 Then

        Print "CRC FAIL (temps frame). Data is corrupted or not a valid MODBUS RTU frame."

        Print

        _Limit pollHz!

        GoTo ContinueLoop

    End If



    ' Basic header checks

    If Asc(resp$, 2) <> &H03 Then

        Print "Unexpected function code:"; Asc(resp$, 2); " (expected 03)."

        Print "NOTE: If you see 0x83, it is an exception response."

        Print

        _Limit pollHz!

        GoTo ContinueLoop

    End If



    If Asc(resp$, 3) <> 16 Then

        Print "Unexpected bytecount:"; Asc(resp$, 3); " (expected 16 for 8 registers)."

        Print

        _Limit pollHz!

        GoTo ContinueLoop

    End If



    ' Decode and print temperatures

    ' Each channel is a signed 16-bit big-endian integer in 0.1°C.

    For i% = 0 To 7

        rawS% = GetS16BE%(resp$, 4 + i% * 2)

        t! = rawS% / 10!

        Print Using "CH# = ####.# C"; i%; t!

    Next i%

    Print "----------------------------"

    Print



    ContinueLoop:

    _Limit pollHz!

Loop



Close #h%

Print "Done."

End









Function Crc16Modbus& (s$)

    ' MODBUS RTU CRC16:

    ' - init 0xFFFF

    ' - polynomial 0xA001 (reflected)

    Dim crc&, i%, j%

    crc& = &HFFFF&

    For i% = 1 To Len(s$)

        crc& = crc& Xor Asc(s$, i%)

        For j% = 1 To 8

            If (crc& And 1) Then

                crc& = (crc& \ 2) Xor &HA001&

            Else

                crc& = crc& \ 2

            End If

        Next j%

    Next i%

    Crc16Modbus& = (crc& And &HFFFF&)

End Function



Function U16BE$ (v&)

    ' Convert 0..65535 into 2 bytes big-endian.

    U16BE$ = Chr$((v& \ 256) And &HFF) + Chr$(v& And &HFF)

End Function



Function HexDump$ (s$)

    ' Render bytes as hex pairs "01 03 00 ..."

    Dim i%, out$

    out$ = ""

    For i% = 1 To Len(s$)

        out$ = out$ + Right$("0" + Hex$(Asc(s$, i%)), 2) + " "

    Next i%

    HexDump$ = out$

End Function



Function ModbusBuildRead$ (slave%, reg&, count%)

    ' Build MODBUS RTU request frame:

    ' [slave][03][regHi][regLo][cntHi][cntLo][crcLo][crcHi]

    Dim req$, crc&

    req$ = Chr$(slave% And &HFF) + Chr$(&H03) + U16BE$(reg&) + U16BE$(count%)

    crc& = Crc16Modbus&(req$)

    req$ = req$ + Chr$(crc& And &HFF) + Chr$((crc& \ 256) And &HFF)

    ModbusBuildRead$ = req$

End Function



Function ModbusCheckCrc% (frame$)

    ' Verify CRC for a complete MODBUS RTU frame.

    ' CRC is stored as [crcLo][crcHi] in the last two bytes.

    Dim n%, crcRx&, crcCalc&

    n% = Len(frame$)

    If n% < 5 Then ModbusCheckCrc% = 0: Exit Function

    crcRx& = Asc(frame$, n% - 1) + 256& * Asc(frame$, n%)

    crcCalc& = Crc16Modbus&(Left$(frame$, n% - 2))

    ModbusCheckCrc% = (crcRx& = crcCalc&)

End Function



Function GetU16BE& (s$, position%)

    ' Read unsigned 16-bit big-endian from s$ at 1-based position.

    Dim hi&, lo&

    hi& = Asc(s$, position%) And &HFF

    lo& = Asc(s$, position% + 1) And &HFF

    GetU16BE& = hi& * 256& + lo&

End Function



Function GetS16BE% (s$, position%)

    ' Read signed 16-bit big-endian (two's complement).

    Dim v&

    v& = GetU16BE&(s$, position%)

    If v& >= 32768& Then v& = v& - 65536&

    GetS16BE% = v&

End Function



Sub SleepMs (ms!)

    ' Simple portable sleep using QB64 _DELAY (seconds).

    _Delay ms! / 1000!

End Sub



Sub SerialWrite (h%, s$)

    ' Write raw bytes one-by-one using PUT (LEN=1 record).

    Dim i%

    For i% = 1 To Len(s$)

        Byte1 = Mid$(s$, i%, 1)

        Put #h%, , Byte1

    Next i%

End Sub



Sub SerialFlush (h%)

    ' Linux-friendly RX flush:

    ' Read and discard bytes for a short time window, without LOC().

    Dim t0!, b$

    t0! = Timer



    Do

        b$ = Input$(1, # h%)

        If Len(b$) = 0 Then

            If (Timer - t0!) > 0.2 Then Exit Do

            SleepMs 5

        Else

            ' Keep flushing while bytes arrive; extend the window slightly.

            t0! = Timer

        End If

    Loop

End Sub



Function SerialReadFrame03$ (h%, expectedSlave%, timeoutSec!)

    ' Read and extract a valid MODBUS function 03 response frame.

    '

    ' Method:

    ' - Accumulate bytes with INPUT$(1,#) until timeout

    ' - Scan buffer for: [addr][03][bytecount][...data...][crcLo][crcHi]

    ' - Verify CRC; return the first valid frame found

    '

    ' expectedSlave%:

    ' - 0 => accept any slave address (useful for broadcast queries)

    ' - else => only accept frames from that slave

    Dim t0!, buf$, b$

    Dim i%, n%, addr%, fn%, bc%, frameLen%

    Dim candidate$



    t0! = Timer

    buf$ = ""

    SerialReadFrame03$ = ""



    Do

        b$ = Input$(1, # h%)

        If Len(b$) > 0 Then

            buf$ = buf$ + b$

            If Len(buf$) > 512 Then buf$ = Right$(buf$, 512)

        Else

            SleepMs 2

        End If



        n% = Len(buf$)

        If n% >= 5 Then

            For i% = 1 To n% - 4

                addr% = Asc(buf$, i%) And &HFF



                If expectedSlave% <> 0 Then

                    If addr% <> (expectedSlave% And &HFF) Then GoTo NextI

                End If



                fn% = Asc(buf$, i% + 1) And &HFF

                If fn% <> &H03 Then GoTo NextI



                bc% = Asc(buf$, i% + 2) And &HFF

                frameLen% = 5 + bc% ' addr+fn+bc + data(bc) + crc(2)



                If (i% + frameLen% - 1) <= n% Then

                    candidate$ = Mid$(buf$, i%, frameLen%)

                    If ModbusCheckCrc%(candidate$) Then

                        SerialReadFrame03$ = candidate$

                        Exit Function

                    End If

                End If



                NextI:

            Next i%

        End If



        If (Timer - t0!) >= timeoutSec! Then Exit Do

    Loop

End Function

Leave dev$ at /dev/ttyUSB0 only if it really exists. Better is /dev/serial/by-id/....
Run the program and send back:
full text of the dump (mainly RX addr: and RX temps, output from the commands that the program prints in the top debug block, confirmation of VIN power.

Once we see the first valid RX addr or RX temps (and it passes the CRC), it's solved and we can continue to temperatures reading.

[Rudy M]

Hi Petr, 

Thank you for the new listings and tips. 
I'll start with a photo of the test setup, adding as much commentary as possible. 
Tomorrow and the day after, I'll further test the two new listings and your tips and publish the results here on the forum. 

Thanks for your enthusiasm. Rudy...

Now the picture of my  test setup:

[Rudy M]

Hi Petr, 

I've been working on the hardware a bit. 

- I installed a small power supply module that maintains the voltage at exactly 30,0 volts (Tested with the "Fluke"). 
- The GND (output of the USB-RS485 adapter) connected to the GND of the PTA8D08 module.
- I tested at new all four listings you provided so far, but I don't see any difference.
-(I also did a test 'switching the A B connections...) 

I wanted to do this first, to address both your and my concerns about the correctness of the electronic setup.

Tomorrow I will try to make a summary of the output you requested from the program or from the Linux system.

Rudy M

[Rudy M]

Hi Petr,
After the installation of the litte powersupply, I let run all 5 listings:
















Info via the commandline in a terminal:

rudy@lenovo:~$ ls -l /dev/serial/by-id
total 0
lrwxrwxrwx 1 root root 13 jan 12 09:59 usb-1a86_USB_Single_Serial_5A98056465-if00 -> ../../ttyACM0

rudy@lenovo:~$ ls -l /dev/ttyUSB*
ls: No acces to '/dev/ttyUSB*':  File or map does not exist

rudy@lenovo:~$ ls -l /dev/ttyACM*
crw-rw---- 1 root dialout 166, 0 jan 12 10:09 /dev/ttyACM0

rudy@lenovo:~$ groups
rudy adm dialout cdrom sudo dip plugdev users lpadmin sambashare

lsof /dev/ttyACM*
comment Rudy: Gives no output

Module Power:
I installed a small stabilized power supply module that can supply up to 4 amps of current.
The voltage regulated to 30.0 volts (Control: with Fluke meter)
Tested with power resistors: The voltage remained exactly at 30.0 volts.
(control with Fluke meter at the tension of 30.0 Volt).
(And the GND of the USB-RS485 adaptor is connected with the GND of the PTA8D08 module)

In the QB64PE map (between the names of the compiled files),
i see a file with this name and no extention:
COM1:9600,N,8,1,BIN,CS0,DS0
large: 897 bytes
(but I can not open this file).

Greatings,
Rudy M

[Rudy M]

Hi Petr,

GOOD NEWS!!!

I did a lot of tests with all Your listings.
This morning I did a last test (Your laste listing), but I swap at new the wires +A -A on the PTA8D08 module.

Bingo!!!
Your listing immediately gave the temperature in degrees Celsius. 
I did another small test and held two PT100 probes between my fingers. 
You can clearly see:
- that the top two temperatures remain at 19.x ° Celcius.
- that the last two temperatures go above 20° ° Celcius. 

The print screen from this test:



The respons is a little bit slower then my old system the DS18B20 sensors, but I do'nt known if it is from the PT100 sensor or from the programlisting.
All in all, I'm very pleased that it's starting to work. 
I'm also going to test today also Your previous programs you created. If I see or find anything relevant, I'll definitely let you know here today.

Greetings,
Rudy M

Quick Edit: After a restart of the PC, i did a test on the responstime, and this is very quick! (4 sensors: 0.13 seconds/sensor)

[Petr]

The program reads temperatures. That's a clear reason to go buy a beer     Thank you for the information. If you need anything else, write it here, please.


Have you solved the switching of outputs according to temperatures with the second board? What is the current load capacity of those relays, what is the power consumption of the heaters, will you power it directly from the second board, or will you use contactors or other auxiliary relays for higher current? Have you solved this yet?