 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : Help with 1-Wire Temp reading.
| Author | Message | ||||
| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Mentioned this in another thread. I'm wondering what's involved in reading multiple DS18B20's on a single data pin. Have read what's done on RPi in Silicon Chips article & get a vague idea, looked at the DS18B20 Data Sheet & see some relevant commands I don't quite understand. Can anyone explain what would be required to:- 1. Read the serial numbers from the individual devices, presumably connected one at a time. 2. Then read a specific sensor on the bus based on it's serial number. I've looked at Geoff's code in the MM Library, ONE_WIRE.BAS & assume if the serial numbers were know, the extra commands could be added to read a specific device. I am aware that the One wire command has been changed since to example was written |
||||
jman Guru Joined: 12/06/2011 Location: New ZealandPosts: 711 |
Hi Unfortunately the OWSEARCH command is no longer supported so you cannot search for multiple devices on the same pin. Below is some updated code to read a single sensor If you really want to do this then maybe ask matherp if this is possible with a CFunction GetTemp 14, Temp, &H7F Print "The temperature is:" Temp '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' Subroutine to get the temperature from a Dallas DS18B20. ' Usage GetTemp (Pin number of DS18B20), (Temperature Variable), (Resolution) ' Resolution Table (Resolution Variable) ' &H1F = 9 bits 93.75ms Conversion Time ' &H3F = 10 Bits 187.5ms Conversion Time ' &H5F = 11 Bits 375ms Conversion Time ' &H7F = 12 Bits 750ms Conversion Time ' Temperature of 127 will be displayed ' in the case of a sensor fault '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' Sub GetTemp (PinNbr, Value, Resolution) Local TH, TL, b, t OneWire Reset PinNbr ' reset OneWire Write PinNbr, 2, 5, &HCC, &H4E, &H00, &H00, Resolution OneWire Write PinNbr, 1, 2, &HCC, &H44 t=Timer Do If Timer - t > 1000 Then Error "Sensor Error" OneWire Read PinNbr, 4, 1, b ' Conversion status Loop Until b = 1 OneWire Write PinNbr, 1, 2, &HCC, &HBE OneWire Read PinNbr, 2, 2, TL, TH Value = ((TH And &b111) * 256 + TL) / 16 If T2 And &b1000 Then Value = -Value ' adjust if negative End Sub Regards Jman |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Found this which might help me identify the sensors & code them manually, or possibly load the data in an array for later use. Not sure what's missing, or how to put it all together. Search routine And this that will read multiple sensors. Multiple OneWire devices on the same bus Just not sure what needs modifying. Any suggestions? Thanks Phil |
||||
| jman Guru Joined: 12/06/2011 Location: New ZealandPosts: 711 |
Hi After a little thought and a look at the datasheet see below for some code that will get your sensors serial and crc Option Explicit Dim OW1,OW2,OW3,OW4,OW5,OW6,OW7,OW8 Dim PinNbr PinNbr = 17 OneWire Reset Pinnbr OneWire Write PinNbr, 1, 1, &H33 ' Issue Read ROM command OneWire Read PinNbr, 2, 8, OW1,OW2,OW3,OW4,OW5,OW6,OW7,OW8 Print "Temp Sensor Should be 28 / ";Hex$(OW1);"H" Print "Ser# ",Hex$(OW2,2);Hex$(OW3,2);Hex$(OW4,2);Hex$(OW5,2);Hex$(OW6,2);Hex$(OW7,2);"H" Print "CRC ";Hex$(OW8,2);"H" Make a note of the details then use the code below to read your sensors I have tried this with two sensors and it seems to work ok. You will need to change the serial and crc to your sensor values IE &H55,&H28,XX,XX,XX,XX,XX,XX,XX,&H44 were xx are your sensor values Option Explicit Dim OW1,OW2,OW3,OW4,OW5,OW6,OW7,OW8 Dim LTemp, HTemp, Value, PinNbr, Status PinNbr = 17 OneWire Reset Pinnbr 'Put 1st sensor serial and crc here &H55,&H28,XX,XX,XX,XX,XX,XX,XX,&H44 OneWire Write PinNbr, 1, 10, &H55,&H28,&H39,&HE5,&H2B,&H06,&H00,&H00,&H58,&H44 StatusCheck 'check sensor is ready OneWire Write PinNbr, 1, 10, &H55,&H28,&H39,&HE5,&H2B,&H06,&H00,&H00,&H58,&HBE OneWire Read PinNbr, 2, 2, LTemp, HTemp TempCalc 'Work out the temp in C Print "1st Sensor ";Value;"C" 'Put 2nd sensor serial and crc here OneWire Write PinNbr, 1, 10, &H55,&H28,&H63,&HDB,&H2A,&H06,&H00,&H00,&H10,&H44 StatusCheck 'check sensor is ready OneWire Write PinNbr, 1, 10, &H55,&H28,&H63,&HDB,&H2A,&H06,&H00,&H00,&H10,&HBE OneWire Read PinNbr, 2, 2, LTemp, HTemp TempCalc 'Work out the temp in C Print "2nd Sensor ";Value;"C" End '========================================================= Sub StatusCheck Timer=0 : Status=0 Do If Timer > 1000 Then Error "Sensor Error" OneWire Read PinNbr, 4, 1, Status ' Conversion status Loop Until Status = 1 End Sub '========================================================= Sub TempCalc Value = ((HTemp And &b111) * 256 + LTemp) / 16 If HTemp And &b1000 Then Value = -Value ' adjust if negative End Sub '========================================================= Hope this helps Regards Jman |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Thanks Jman. I run the first routine & it returns:- Temp Sensor Should be 28 / 28H Ser# FFA667A81501H CRC 6FH 13 Plus 3 characters Vs 14 in the string above. Just not sure how that fits in with the line below. 'Put 1st sensor serial and crc here &H55,&H28,XX,XX,XX,XX,XX,XX,XX,&H44 OneWire Write PinNbr, 1, 10, &H55,&H28,&H39,&HE5,&H2B,&H06,&H00,&H00,&H58,&H44 Phil |
||||
| jman Guru Joined: 12/06/2011 Location: New ZealandPosts: 711 |
Hi Phil Your sensor details inserted would be as below Remember when checking for the serial numbers you can only have ONE sensor connected at a time &H55,&H28,&HFF,&HA6,&H67,&HA8,&H15,&H01,&H6F,&H44 Regards Jman |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Thanks again, My rusty memory really showing here. I was considering the "H" in both strings to be part of the serial$ & CRC. It's been a while.... Was aware of the single device limitation for obtaining the Serial#'s Cheers. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Still not having complete success here. Still only have a single device on Pin 22, and it's working Ok with the TEMPR() command. I can read the ID of the sensor Ok with either of Jmans routines, but am not reading the temp successfully. > RUN
LTemp 255 HTemp 255 1st Sensor -127.938C > Seems like ONEWIRE READ is returning 255 for the 2 variables. Option Explicit
Dim OW1,OW2,OW3,OW4,OW5,OW6,OW7,OW8 Dim LTemp, HTemp, Value, PinNbr, Status PinNbr = 22 OneWire Reset Pinnbr 'Put 1st sensor serial and crc here &H55,&H28,XX,XX,XX,XX,XX,XX,XX,&H44 OneWire Write PinNbr, 1, 10, &H55,&H28,&HFF,&HA6,&H67,&HA8,&H15,&H01,&H6F,&H44 StatusCheck 'check sensor is ready OneWire Write PinNbr, 1, 10, &H55,&H28,&HFF,&HA6,&H67,&HA8,&H15,&H01,&H6F,&HBE OneWire Read PinNbr, 2, 2, LTemp, HTemp print "LTemp", LTemp print "HTemp", HTemp TempCalc 'Work out the temp in C Print "1st Sensor ";Value;"C" 'Put 2nd sensor serial and crc here 'OneWire Write PinNbr, 1, 10, &H55,&H28,&H63,&HDB,&H2A,&H06,&H00,&H00,&H10,&H44 'StatusCheck 'check sensor is ready 'OneWire Write PinNbr, 1, 10, &H55,&H28,&H63,&HDB,&H2A,&H06,&H00,&H00,&H10,&HBE 'OneWire Read PinNbr, 2, 2, LTemp, HTemp 'TempCalc 'Work out the temp in C 'Print "2nd Sensor ";Value;"C" End '========================================================= Have my correct ID & just commented out the 2nd sensor code & added Print to LTemp & HTemp. Any ideas where I'm going wrong? Cheers Phil |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Ok, Back to basics regarding the above post. Do the DS18B20's work as multiple devices on a single bus in parasitic mode? Just noticed in Table 3, Page 12 of the Data Sheet that it's mentioned that the 44h command is not applicable for parasite powered DS18B20s. So am I correct in now thinking I need the devices correctly powered & data on it's own wire. Thanks. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
More confused now...... The flow chart on page 14 seems to indicate that the 44h command can be used in parasite power mode. |
||||
| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Finding the examples above to be very useful in overcoming the need to cable each sensor back to the MicroMite. Currently considering a 2nd project for household heating & ventilation control, which would benefit from a large number of sensors, and be a nightmare to implement if each had to wire back to the MicroMite individually. Has me thinking whether the code would be worth porting to a cFunction or 2. Maybe one to find the sensors on a given pin and a second to read them individually or as a group. I do notice Jman Dim'ed some variables in the code above that were not used.... Option Explicit
Dim OW1,OW2,OW3,OW4,OW5,OW6,OW7,OW8 Dim LTemp, HTemp, Value, PinNbr, Status PinNbr = 22 Cheers Phil |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
