Is it possible to adjust the resolution of the ds18b20, e.g. 10 or 12 bits?

[Nulista]

Hi ,
Is it possible to adjust the resolution of the ds18b20, e.g. 10 or 12 bits?

thx

[mathieucarbou]

Why ? What would be your use case ?

The DS18 series (specifically the DS18B20) offers a resolution of 9 to 12 bits with a factory-specified accuracy of ±0.5°C between -10°C and +85°C. This makes them moderately accurate sensors, but not designed for super-high-precision temperature readings.

So even if you would change the resolution to one of these:

• 9-bit resolution: 0.5°C increments (93.75ms conversion time)
• 10-bit resolution: 0.25°C increments (187.5ms conversion time)
• 11-bit resolution: 0.125°C increments (375ms conversion time)
• 12-bit resolution: 0.0625°C increments (750ms conversion time)​

You are still within the error rate of +/- 0.5C.

Also, there is no compensation: if you place different DS18 next to another one, they do not show the same temp because they sometimes need a little calibration.

They are good to show the relative increase or decrease in temp, or to show a human readable temp. But changing the resolution to have more or less details for them is useless IMO.

The lib internally does a rounding and only triggers a change event of the change is above a threshold. I will remove this rounding.

  read = round(read * 100.0f) / 100.0f;
  const bool changed = std::abs(read - _temperature) >= MYCILA_DS18_RELEVANT_TEMPERATURE_CHANGE || !isValid();

But as to allow the resolution to be changed... What would be your use case exactly ?

[mathieucarbou]

You will be able to play with the Resolution.ino example

[   576][I][MycilaDS18.cpp:28] begin(): [DS18] Searching for DS18 sensor on pin: 18...
[   689][I][MycilaDS18.cpp:40] begin(): [DS18] Found DS18B20 sensor at address 0x6ba9645509646128 on pin: 18 (remaining search count: 9)
[   709][I][MycilaDS18.cpp:44] begin(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18 enabled!
Current resolution: 12-bit
Conversion time: 750 ms
=========== After Setup Start ============
INTERNAL Memory Info:
------------------------------------------
  Total Size        :   375168 B ( 366.4 KB)
  Free Bytes        :   328404 B ( 320.7 KB)
  Allocated Bytes   :    38684 B (  37.8 KB)
  Minimum Free Bytes:   322320 B ( 314.8 KB)
  Largest Free Block:   110580 B ( 108.0 KB)
------------------------------------------
GPIO Info:
------------------------------------------
  GPIO : BUS_TYPE[bus/unit][chan]
  --------------------------------------  
     1 : UART_TX[0]
     3 : UART_RX[0]
============ After Setup End =============
[   822][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.500000 °C
Temperature changed: 23.500000°C
[  1707][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.562500 °C
Temperature changed: 23.562500°C
[  2592][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.500000 °C
Temperature changed: 23.500000°C
[  8727][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.437500 °C
Temperature changed: 23.437500°C
Changing resolution to 9-bit
[ 10488][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 9-bit (94 ms conversion time)
Current resolution: 9-bit
Conversion time: 94 ms
[ 10526][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.500000 °C
Temperature changed: 23.500000°C
[ 11413][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.562500 °C
Temperature changed: 23.562500°C
[ 12518][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.625000 °C
Temperature changed: 23.625000°C
[ 14061][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.687500 °C
Temperature changed: 23.687500°C
[ 15385][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.750000 °C
Temperature changed: 23.750000°C
[ 16709][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.812500 °C
Temperature changed: 23.812500°C
[ 17376][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.875000 °C
Temperature changed: 23.875000°C
[ 18700][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 23.937500 °C
Temperature changed: 23.937500°C
[ 20024][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.000000 °C
Temperature changed: 24.000000°C
Changing resolution to 10-bit
[ 20692][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 10-bit (188 ms conversion time)
Current resolution: 10-bit
Conversion time: 188 ms
[ 21357][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.062500 °C
Temperature changed: 24.062500°C
[ 22619][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.125000 °C
Temperature changed: 24.125000°C
[ 24507][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.187500 °C
Temperature changed: 24.187500°C
[ 26708][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.250000 °C
Temperature changed: 24.250000°C
[ 28909][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.312500 °C
Temperature changed: 24.312500°C
[ 30484][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.375000 °C
Temperature changed: 24.375000°C
Changing resolution to 11-bit
[ 30808][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 11-bit (375 ms conversion time)
Current resolution: 11-bit
Conversion time: 375 ms
[ 33347][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.437500 °C
Temperature changed: 24.437500°C
[ 35857][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.500000 °C
Temperature changed: 24.500000°C
[ 39367][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.562500 °C
Temperature changed: 24.562500°C
Changing resolution to 12-bit
[ 40878][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 12-bit (750 ms conversion time)
Current resolution: 12-bit
Conversion time: 750 ms
[ 43542][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.625000 °C
Temperature changed: 24.625000°C
[ 47052][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.687500 °C
Temperature changed: 24.687500°C
[ 50562][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.750000 °C
Temperature changed: 24.750000°C
Changing resolution to 9-bit
[ 51448][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 9-bit (94 ms conversion time)
Current resolution: 9-bit
Conversion time: 94 ms
[ 58495][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.687500 °C
Temperature changed: 24.687500°C
[ 58724][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.750000 °C
Temperature changed: 24.750000°C
[ 59391][D][MycilaDS18.cpp:155] read(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: 24.687500 °C
Temperature changed: 24.687500°C
Changing resolution to 10-bit
[ 61592][I][MycilaDS18.cpp:190] setResolution(): [DS18] DS18B20 0x6ba9645509646128 @ pin 18: Resolution set to 10-bit (188 ms conversion time)
Current resolution: 10-bit
Conversion time: 188 ms

[mathieucarbou]

Ah wait... resolution set/get does not work...

[mathieucarbou]

ok so the only thing I can do is allow you to configure the threshold (see threshold.ino example) to set it to 0 in order to be called for any temperature change.

Default resolution of ds18 seems to be 12 bits so the default is good enough. Temp should not be read at an interval less than about 1 sec

[Nulista]

Yes, that's right, the temperature varies quite a bit...
But it could work perfectly for me.
I also see that the runtime for "temp.read()" is 25msec.

Thanks!

[mathieucarbou]

I also see that the runtime for "temp.read()" is 25msec.

This is async: read is just sending a request to get a new reading. It does not wait for the response to arrive and be parsed.
It also checks if a reading is available. So if called too often, it can at the opposite make your ds18 less stable.

What is does exactly:

• read the newly made available data (if received)
• request a new reading.