Wrong temperature calculation with a DS18S20 sensor at negative temperatures

[tanoko]

PROBLEM DESCRIPTION

A clear and concise description of what the problem is. This problem was already addressed in issue #5375, which has been closed though user wecl wrote: 'But i didn't test the calculation when the temperature is lower than 0 degrees.'. I used a mix of sensors DS18S20 and DS18B20 to monitor temperatures in a refrigerator and observed strange zigzag shaped plots from DS18S20 sensor placed in the freezer (negative Centigrade). Checking the problem with different GPIO numbers and different modules (D1 mini, ESP-12F, ESP-3M) brought no difference. This behavior is illustrated on plots made with a DS18S20 and DS18B20 placed at the same point when crossing the 0°C mark:

Then I tried to analyze the code of the file xsns_05_ds18x20.ino and found out, that this part of the code must cause the problem: case DS18S20_CHIPID: { if (data[1] > 0x80) { data[0] = (~data[0]) +1; sign = -1; // App-Note fix possible sign error } float temp9 = (float)(data[0] >> 1) * sign; ds18x20_sensor[index].temperature = ConvertTemp((temp9 - 0.25) + ((16.0 - data[6]) / 16.0)); ds18x20_sensor[index].valid = SENSOR_MAX_MISS; return true; }

Instead of the unsigned variable temp9 I used a signed one, which I named tempS and replaced this part of the code by: case DS18S20_CHIPID: { int16_t tempS = (((data[1] << 8) | (data[0] & 0xFE)) << 3) | ((0x10 - data[6]) & 0x0F); ds18x20_sensor[index].temperature = ConvertTemp(tempS * 0.0625 - 0.250); ds18x20_sensor[index].valid = SENSOR_MAX_MISS; return true; }

The result you can see on these plots:

REQUESTED INFORMATION

Make sure your have performed every step and checked the applicable boxes before submitting your issue. Thank you!

• [ x ] Read the Contributing Guide and Policy and the Code of Conduct
• [ x ] Searched the problem in issues
• [ x ] Searched the problem in the docs
• [ x ] Searched the problem in the forum
• [ x ] Searched the problem in the chat
• [ x ] Device used (e.g., Sonoff Basic): Generic (18)
• [ x ] Tasmota binary firmware version number used: 8.1.0
  • [ ] Pre-compiled
  • [ x ] Self-compiled
  • [ x ] IDE / Compiler used: PlatformIO
• [ x ] Flashing tools used: CH340 based adapter
• [ ] Provide the output of command: Backlog Template; Module; GPIO 255: 18:45:59 MQT: stat/tasmota/RESULT = {"NAME":"Fridge","GPIO":[0,148,56,149,4,0,0,0,5,0,6,0,0],"FLAG":0,"BASE":18} 18:45:59 MQT: stat/tasmota/RESULT = {"Module":{"0":"Fridge"}} 18:46:00 MQT: stat/tasmota/RESULT = {"GPIO0":{"0":"None"},"GPIO1":{"148":"Serial Tx"},"GPIO2":{"56":"Led1i"},"GPIO3":{"149":"Serial Rx"},"GPIO4":{"4":"DS18x20"},"GPIO5":{"0":"None"},"GPIO9":{"0":"None"},"GPIO10":{"0":"None"},"GPIO12":{"5":"I2C SCL"},"GPIO13":{"0":"None"},"GPIO14":{"6":"I2C SDA"},"GPIO15":{"0":"None"},"GPIO16":{"0":"None"}} Configuration output here:

- [ x ] If using rules, provide the output of this command: `Backlog Rule1; Rule2; Rule3`:
18:48:59 MQT: stat/tasmota/RESULT = {"Rule1":"ON","Once":"OFF","StopOnError":"OFF","Free":435,"Rules":"ON MCP230_OUT#OUT_D15 DO backlog sensor29 15,1; delay 1; sensor29 15,0 ENDON"}
18:48:59 MQT: stat/tasmota/RESULT = {"Rule2":"OFF","Once":"OFF","StopOnError":"OFF","Free":511,"Rules":""}
18:49:00 MQT: stat/tasmota/RESULT = {"Rule3":"OFF","Once":"OFF","StopOnError":"OFF","Free":511,"Rules":""}
  Rules output here:
18:50:44 RUL: MCP230_OUT#OUT_D15 performs "backlog sensor29 15,1; delay 1; sensor29 15,0"
18:50:44 MQT: stat/tasmota/RESULT = {"S29cmnd_D15":{"COMMAND":"ON","STATE":"ON"}}
18:50:44 MQT: stat/tasmota/RESULT = {"Delay":2}
18:50:45 MQT: stat/tasmota/RESULT = {"S29cmnd_D15":{"COMMAND":"OFF","STATE":"OFF"}}

``` has no relevance to discussed problem...
- [ ] Provide the output of this command: `Status 0`:

  STATUS 0 output here:
18:58:02 MQT: stat/tasmota/STATUS = {"Status":{"Module":0,"FriendlyName":["Tasmota-6215"],"Topic":"tasmota","ButtonTopic":"0","Power":0,"PowerOnState":3,"LedState":7,"LedMask":"FFFF","SaveData":1,"SaveState":1,"SwitchTopic":"0","SwitchMode":[0,0,0,0,0,0,0,0],"ButtonRetain":0,"SwitchRetain":0,"SensorRetain":0,"PowerRetain":0}}
18:58:02 MQT: stat/tasmota/STATUS1 = {"StatusPRM":{"Baudrate":115200,"GroupTopic":"tasmotas","OtaUrl":"http://thehackbox.org/tasmota/release/tasmota.bin","RestartReason":"Power on","Uptime":"8T01:16:28","StartupUTC":"2020-06-16T15:41:34","Sleep":50,"CfgHolder":4617,"BootCount":103,"SaveCount":550,"SaveAddress":"F9000"}}
18:58:02 MQT: stat/tasmota/STATUS2 = {"StatusFWR":{"Version":"8.1.0(lite)","BuildDateTime":"2020-05-08T16:44:42","Boot":31,"Core":"2_6_1","SDK":"2.2.2-dev(38a443e)","Hardware":"ESP8285","CR":"366/699"}}
18:58:02 MQT: stat/tasmota/STATUS3 = {"StatusLOG":{"SerialLog":2,"WebLog":2,"MqttLog":0,"SysLog":0,"LogHost":"","LogPort":514,"SSId":["unknown",""],"TelePeriod":60,"Resolution":"D58180C0","SetOption":["00008009","2805C8000100060000005A00000000000000","00000000","00000000"]}}
18:58:02 MQT: stat/tasmota/STATUS4 = {"StatusMEM":{"ProgramSize":483,"Free":520,"Heap":26,"ProgramFlashSize":1024,"FlashSize":1024,"FlashChipId":"144051","FlashMode":3,"Features":["00000809","8F282185","040013A0","00008441","010000F1","00000010"],"Drivers":"1,2,9,10,13","Sensors":"1,2,5,9,12,29,54"}}
18:58:02 MQT: stat/tasmota/STATUS5 = {"StatusNET":{"Hostname":"tasmota-6215","IPAddress":"192.168.111.109","Gateway":"192.168.111.11","Subnetmask":"255.255.255.0","DNSServer":"192.168.111.11","Mac":"84:0D:8E:72:78:47","Webserver":2,"WifiConfig":4}}
18:58:02 MQT: stat/tasmota/STATUS6 = {"StatusMQT":{"MqttHost":"192.168.111.168","MqttPort":1883,"MqttClientMask":"DVES_%06X","MqttClient":"DVES_727847","MqttUser":"DVES_USER","MqttCount":2,"MAX_PACKET_SIZE":1000,"KEEPALIVE":30}}
18:58:02 MQT: stat/tasmota/STATUS7 = {"StatusTIM":{"UTC":"Wed Jun 24 16:58:02 2020","Local":"Wed Jun 24 18:58:02 2020","StartDST":"Sun Mar 29 02:00:00 2020","EndDST":"Sun Oct 25 03:00:00 2020","Timezone":99,"Sunrise":"04:54","Sunset":"20:58"}}
18:58:02 MQT: stat/tasmota/STATUS10 = {"StatusSNS":{"Time":"2020-06-24T18:58:02","DS18S20-1":{"Id":"0008035561F0","Temperature":2.938},"DS18S20-2":{"Id":"000803556EC3","Temperature":4.437},"DS18S20-3":{"Id":"00080355AC44","Temperature":5.562},"DS18S20-4":{"Id":"000803619FA0","Temperature":44.813},"DS18S20-5":{"Id":"000803629DBA","Temperature":23.563},"DS18S20-6":{"Id":"00080362F981","Temperature":4.000},"DS18B20-7":{"Id":"0114553E57AA","Temperature":-2.188},"DS18B20-8":{"Id":"01145546B2AA","Temperature":2.438},"DS18B20-9":{"Id":"01145577E5AA","Temperature":1.875},"DS18B20-10":{"Id":"011455811CAA","Temperature":-16.250},"DS18B20-11":{"Id":"01145587CDAA","Temperature":-19.500},"ADS1115":{"A0":3134 ...
18:58:02 MQT: stat/tasmota/STATUS11 = {"StatusSTS":{"Time":"2020-06-24T18:58:02","Uptime":"8T01:16:28","UptimeSec":695788,"Heap":26,"SleepMode":"Dynamic","Sleep":50,"LoadAvg":38,"MqttCount":2,"POWER":"OFF","Wifi":{"AP":1,"SSId":"unknown","BSSId":"14:CC:20:2F:A6:3E","Channel":7,"RSSI":54,"Signal":-73,"LinkCount":1,"Downtime":"0T00:00:06"}}}

• [ ] Provide the output of the Console log output when you experience your issue; if applicable: (Please use weblog 4 for more debug information)

  
  Console output here:

### TO REPRODUCE
_Steps to reproduce the behavior:_
Check the readings of a DS18S20 at slow enough changes of temperature, when it's below 0°C and compare the readings with another sensor (e.g. DS18B20)

### EXPECTED BEHAVIOUR
_A clear and concise description of what you expected to happen._
I think, the attached plots explain it clear enough.

### SCREENSHOTS
_If applicable, add screenshots to help explain your problem._

### ADDITIONAL CONTEXT
_Add any other context about the problem here._
Sorry, when my code is not perfect, but I'm not a software developer...
N.B. I'm using the SW Version 8.1.0, but as I can see, this part of the code is still the same in the newest version.

**(Please, remember to close the issue when the problem has been addressed)**

[tanoko]

Recently, I repeated tests of the temperature sensor DS18S20 with Tasmota V. 8.3.1. Here the plot with the pre-compiled version of tasmota.bin:

Then, I modified the file xsns_05_ds18x20.ino as described above and compiled the tasmota.bin using PlatformIO. The result may be seen on the plot below made under similar conditions as the first one:

Here the output of Status 2 on the console: 08:54:47 MQT: stat/tasmota_08DE86/STATUS2 = {"StatusFWR":{"Version":"8.3.1(tasmota)","BuildDateTime":"2020-07-03T10:58:41","Boot":31,"Core":"2_7_1","SDK":"2.2.2-dev(38a443e)","Hardware":"ESP8266EX","CR":"394/699"}}

[ascillato2]

Cool, Thanks for sharing. Please help us and provide a PR. Thanks.