DS18B20 value -127º, but only when connecting to Blynk, on ESP32

Northernboy · November 2, 2017, 4:46pm

@Costas I’m glad it worked for you. I am looking into how to modify the tick frequency to try to give the Onewire function more time to complete. I believe the bad readings are because the task is existing before it has time to get a value. I’ll report back once I get some more testing and tuning.

distans · November 2, 2017, 6:15pm

I don’t know if my previous post was overlooked or just ignored but I still believe its valid and worth looking into.

Use two timers instead of waiting for the temperature conversation to finish!

Following @Costas example I did a run for 200 reading, with three sensors in parasitic mode, with a total cable lenght of 17 meters, only powered by the Arduino and got ZERO errors. Albeit not a dual core MCU, but all my timing issues are gone with this setup!


The best is yet to come!
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Costas · November 2, 2017, 6:31pm

Got more errors on the ESP32 with this setting than the test without it.

Just running another test at 9 bit resolution.

95	23.81	Errors: 5
96	23.81	Errors: 5
97	23.87	Errors: 5
98	23.87	Errors: 5
99	23.87	Errors: 5
100	23.87	Errors: 5
101	23.87	Errors: 5
102	-127.00	Errors: 6
103	23.87	Errors: 6
104	23.87	Errors: 6
105	23.81	Errors: 6

Already 6 errors from 105 readings. 12 errors from 200 readings.

Northernboy · November 2, 2017, 6:31pm

@distans I’ve used the wait for conversion in the past and it does work great. However I believe it is not problem with the ESP32. FreeRTOS freezes tasks and switches to another if there is one with a higher priority, I feel that this momentary pause effects some of timing in onewire function. If you look at the library there are delays in the microSeconds and it also disables interrupts during this timing. I could be wrong but it seems this way is working for now and I am still researching and learning.

distans · November 2, 2017, 7:10pm

Mkay, that’s seems weird!

Well yes (and no) When I use setWaitForConversion(false), it takes requestTemperature() less than 2 ms to send the command to the sensors. When I check back, the reading takes about 30 ms.

Have you tried using deviceAddress instead of getTempCByIndex? It’s a little bit faster.

Northernboy · November 2, 2017, 8:06pm

@distans are you testing on a ESP32 with wifi enabled?

distans · November 2, 2017, 8:50pm

No, I only have Arduino UNO’s at the moment and using W5100 Ethernet shield (only outdated cheap stuff hehe). I had a fair amount of issues with disconnects before. I even tapped the network connection and dumped all traffic thru Wireshark. It seemed like the problem was due to the W5100’s small RX buffer got full when left unattended for a period of time (i.e. the program was stuck on a functions delay).

But after I rearranged how I call the sensors and a more modest polling for external data (time and connection) I haven’t had any problem.

I’ve been thinking about buying an ESP32 or two, but I’m not so sure anymore But I hope you figure it out!

Costas · November 2, 2017, 8:53pm

If you want something that works buy an ESP8266.

psoro · November 2, 2017, 10:16pm

@Northernboy,
It’s working now! Unfortunately I’ve got the same fails as using a “normal” sketch… Anyway I have learnt a little bit more about the ESP32 and at least I can use both cores to do different things in a proper way.

Northernboy · November 2, 2017, 11:07pm

I think I may have found a fix. Testing it now 250 reads and no failures. I going to try to modify the onewire library so it will work however you run it. Ill report back later after more testing.

Northernboy · November 3, 2017, 12:20am

I tested it on two of the above scripts and it works perfect without any need to do anything with tasks or programming both Cores.

First initialize the sensor in setup before starting Blynk.
Then after whenever reading the sensor a command before to stop interrupts and after to start interrupts
See the following example:

void temp_read()
{
  portDISABLE_INTERRUPTS();
  DS18B20.requestTemperatures();
  temp = DS18B20.getTempCByIndex(0);
  portENABLE_INTERRUPTS();
 
  Serial.println("TEMP");
  Serial.println(temp);
 
  Blynk.virtualWrite(V0, temp);
}

I think this is stopping any of the multitasking that is enabled with the wifi on.

Give it a try and let me know.

Costas · November 3, 2017, 12:53am

Looking excellent here, this is how the trusty DS18B20 should perform:

90	23.50	Errors: 0
91	23.50	Errors: 0
92	23.50	Errors: 0
93	23.44	Errors: 0
94	23.44	Errors: 0
95	23.44	Errors: 0
96	23.50	Errors: 0
97	23.50	Errors: 0
98	23.50	Errors: 0
99	23.50	Errors: 0
100	23.44	Errors: 0
101	23.50	Errors: 0
102	23.50	Errors: 0
103	23.44	Errors: 0
104	23.50	Errors: 0
105	23.50	Errors: 0
106	23.44	Errors: 0
107	23.44	Errors: 0
108	23.44	Errors: 0
109	23.50	Errors: 0
110	23.44	Errors: 0
111	23.50	Errors: 0
112	23.50	Errors: 0
113	23.50	Errors: 0
114	23.50	Errors: 0
115	23.44	Errors: 0
116	23.50	Errors: 0
117	23.44	Errors: 0
118	23.44	Errors: 0
119	23.50	Errors: 0
120	23.50	Errors: 0
121	23.44	Errors: 0

Thanks for the fix.
I will change the timer to 30s and leave it running for a few hours.

Still going strong:

357	23.56	Errors: 0
358	23.56	Errors: 0
359	23.56	Errors: 0
360	23.56	Errors: 0
361	23.56	Errors: 0
362	23.56	Errors: 0
363	23.56	Errors: 0
364	23.56	Errors: 0
365	23.56	Errors: 0
366	23.56	Errors: 0
367	23.56	Errors: 0
368	23.56	Errors: 0
369	23.56	Errors: 0
370	23.56	Errors: 0
371	23.50	Errors: 0
372	23.56	Errors: 0
373	23.50	Errors: 0
374	23.50	Errors: 0
375	23.50	Errors: 0
376	23.50	Errors: 0

Costas · November 3, 2017, 1:41am

/* RGB-DS18B20-OTA.ino RGB with DS18B20, local OTA and timers for ESP32 
from https://community.blynk.cc/t/esp32-pwm-and-blynk/18277
and https://community.blynk.cc/t/ds18b20-value-127-but-only-when-connecting-to-blynk-on-esp32/18336/112
and https://community.blynk.cc/t/starting-an-esp32-thread/18809 (Lounge)
and https://community.blynk.cc/t/timer-help/18812
*/

thiagopai · November 3, 2017, 1:08pm

I am happy that the topic is generating good results, I had a health problem (herniated disc crisis), and I will follow the tests and suggestions posted here in the topic.

Costas · November 3, 2017, 5:07pm

Update:

748	23.31	Errors: 0
749	23.31	Errors: 0
750	23.25	Errors: 0
751	23.37	Errors: 0
[23481449] Time sync: OK
752	23.44	Errors: 0
753	23.37	Errors: 0
754	23.50	Errors: 0
755	23.56	Errors: 0

psoro · November 3, 2017, 5:54pm

woohoo!

TEMPERATURE: 
23.62
FAILS: 
0
READINGS: 
1601

Many thanks for that tips!!

Costas · November 3, 2017, 6:05pm

Go steady with the EEPROM.

thiagopai · November 7, 2017, 1:56pm

I’m really very happy, this code it was the only one that really worked, and best of all, no mistakes.
Thank you very much for the help the all.

poolsaliba123 · March 2, 2018, 6:48pm

HI I have encountered the same problem, can you send me your program please because it tried to follow the steps but still it doesnt work.

Kajsa · March 27, 2019, 9:22am

Use your own code that u use for Blynk but change your reading to Northernboy void temp_read()
It works for me, good luck.