Velleman MM101 User manual

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USER MANUAL FEBRUARY 2016
MM101
DIGITAL SENSOR TEMPERATURE BOARD

2
MM101USER MANUAL
This temperature sensor provides a digital output signal to
allow easy interfacing to a microcontroller or a micropro-
cessor using the 1-Wire® communication protocol. Since
communication with the sensor is digital, it can be placed
at a distance from the controller circuit without worrying
about disturbances and interference from the surrounding
environment.
The thermal sensor board uses three connections: Vcc
(5V power), GND and a bidirectional data line (DQ). The
DS18B20’s temperature measurements range between
-55°C and +125° C and are expressed in 9 to 12 bit reso-
lution (user denable) with ±0.5°C accuracy in the -10°C
to 85°C range. Resolution is set through the conguration
register.
USING THE SENSOR
Red wire
5V positive
power supply
Black wire
GND negative
power supply
Yellow wire
Temperature output/
data request
To begin temperature measurement and A/D
conversion the “Convert T” (code: 44h) command
is issued. The sensor transmits a 0 during the
conversion and returns a 1 when the operation is
complete. The resulting two bytes are available
in the sensor’s scratchpad memory and corre-
spond to the measured temperature, expressed
in Celsius. The “Read ScratchPad” (code: BEh)
command is used to access the measurement
from memory. The 2-byte register (for an 11-bit
sampling) is structured as shown in Fig. 1. The
structure of the 2 bytes returned in 11-bit mode
are as follows: the rst 11 bits (including all of the
least signicate byte and the rst three bits from
the most signicate byte) express the temperature
value, the last ve express the sign and are all 0’s
if the temperate is positive (above zero) and all 1’s
if the temperature is negative (below zero).
The DS18B20 is capable of expressing temperatures with decimal values. Looking at Fig. 1, you will see that the
rst four least signicant bit values are less than 1. The rst one 0.0625, the second one is 0.125, that the third
one is 0.25 and that the fourth one is 0.5.
Fig. The structure of the two bits successively emitted by the MM101, each time it is queried: the LS byte is
the one weighing less, while the MSB byte is the more signicate one. This structure is referred to as an 11-bit
representation, plus sign.

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MM101USER MANUAL
For the complete list of specications and commands for the DS18B20 temperature sensor, refer to the datasheet and applica-
tions notes from Maxim Integrated™. Available for download from www.maximintegrated.com.
The complete article concerning this project is published in: Elettronica In, issue n.191
Here’s an example of a measurement with a decimal value:
Suppose a measurement is taken for a positive value of 64.25°C. The two bytes returned will be 00000100
(MSB) and 00000100 (LSB). Referring to gure 1 again, you will see that the LSB returned a value of 0.25 and
the MSB returned a value of +64 degrees.
For 12-bit resolution all the bits will contain data, for 11-bit resolution bit 0 is undened, for 10-bit resolution bits 1
and 0 are undened and for 9-bit resolution bits 2, 1 and 0 are undened.
Considering the data as a whole (composed of the two bytes) the possible output range of the DS18B20 is be-
tween 11111101101110000(-55 °C) and 0000011111010000 (+125°C).
These values can then be converted to hexadecimal format: AB70h and 07D0h, continuing conversion to hexa-
decimal, we see that a temperature value of 10.125C corresponds to 00A2h, while a value of -20C would be
written BCC0h.
EXAMPLE

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ORDERCODE: MM101
REVISION: HMM101