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Author: dany
Last Updated: 2016-02-23
Package Version: 1.0.0.0
Example: 1.0.0.0
Category: Measurement
Downloaded: 1257 times
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License: MIT license
The DS18(S)20, DS18B20 device usage plus the DS1820 Lib and OW_Utilities Lib usage. Also some errors in the mE example (compiler help) are stated.
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Description of how to use the digital tempsensor DS1820, DS18S20 and DS18B20 together with the DS1820 library (http://www.libstock.com/projects/view/104/tempsensors) and the OW_Utilities library (http://www.libstock.com/projects/view/823/ow-utilities).
mE compiler help errors in the one_wire library example:
1. The waiting time between starting the temperature conversion in the DS18x20 and reading out its temperature is only 120 microseconds. The DS18S20 datasheet shows it can take up to 750 millisecs to convert the temperature to a value. So, the code should look like:
//--- Perform temperature reading
Ow_Reset(PORTE, 2); // Onewire reset signal
Ow_Write(PORTE, 2, 0xCC); // Issue command SKIP_ROM
Ow_Write(PORTE, 2, 0x44); // Issue command CONVERT_T
Delay_ms(750); // <---- in stead of delay_us(120)
Ow_Reset(PORTE, 2);
Ow_Write(PORTE, 2, 0xCC); // Issue command SKIP_ROM
Ow_Write(PORTE, 2, 0xBE); // Issue command READ_SCRATCHPAD
temp := Ow_Read(PORTE, 2);
temp := (Ow_Read(PORTE, 2) shl 8) + temp;
//--- Format and display result on Lcd
...
The other delay in the main loop can be left out: Delay_ms(520);
The other delay in the main loop can be left out: Delay_ms(520);
2. The "shift" of the temperature value of the DS18x20 is NOT dependant on the resolution, but on the DS18x20 type: DS18S20 or DS18B20.
In the DS18S20 case the shift is always 1, in the DS18B20 case, the shift is always 4, irrespective of the resolution.
So, this code is NOT correct:
const RES_SHIFT = TEMP_RESOLUTION - 8;
it should be something like this:
var Res_Shift: byte;
...
if DS1820_Family = 'B' // DS18B20
then Res_Shift := 4
else Res_Shift = 1;
See http://www.libstock.com/projects/view/104/tempsensors for the definition of "DS1820_Family".
Of course the variable Res_Shift can also be set manually to 1 or 4 depending on the type of DS18x20 used.
3. The comment on the DS18x20 resolution is wrong:
// Set TEMP_RESOLUTION to the corresponding resolution of used DS18x20 sensor:
// 18S20: 9 (default setting; can be 9,10,11,or 12)
// 18B20: 12
It should be:
// 18S20: 9
// 18B20: 12 (default setting; can be 9,10,11,or 12)
See also http://www.mikroe.com/forum/viewtopic.php?f=86&t=57177&hilit=+ds18s20 and http://www.mikroe.com/forum/viewtopic.php?f=5&t=16225&hilit=+ds18s20 for the forum posts concerning these issues.
