17-05-2012, 12:18 PM
Wireless Temperature and Humidity Sensor Using TELRAN
[attachment=22228]
Introduction
This application note describes the design of a wireless temperature and relative humidity system
based on the TZ1053 TELRAN chip. The TELRAN chip is an ultra low power RF chip operating in
the license free ISM bands (EU 862MHz – 870MHz, USA 902MHz – 928MHz; Japan: 950MHz –
956MHz and China: 779-787MHz). An example design of a wireless temperature and humidity
system is shown (Fig 1) using the SHT21 temperature and humidity sensor from SensirionÔ
Such systems can be used in homes and offices for temperature and humidity
monitoring. They also find uses in automobiles, air conditioning systems and for remote temperature
and humidity monitoring in industry. A schematic of the system is shown in Figure 4. This schematic
shows the wireless temperature and humidity system made up of an SHT21 sensor interfaced to the
TELRAN chip via I2C interface.
Wireless Temperature
and Humidity Sensor Using TELRAN
Application note TZ1053AN-06 Oct 2011
Abstract Dr. C. Uche
This application note describes the complete system design (hardware and software) of a wireless
temperature and humidity monitoring system based on the TZ1053 ultra-low power wireless
TELRAN chip. The wireless temperature and humidity system can measure temperatures from 0°C
to +70°C where the sensor is co-located with TELRAN. The range for temperature can be extended
to -40°C to +120°C and for relative humidity 0 to 100% where the sensor is remote from TELRAN.
Design Considerations
Designing the TELRAN-based wireless temperature and humidity system involves interfacing the
TELRAN radio frequency module (RFM) to the SHT21 via I2C serial interface. As shown in the
design of Figure 4 the I2C data line i.e. SDA is connected to pin 14 (GPIO 2/SDA) input of the
TELRAN RFM. This connection requires a 10kohm pull-up resistor. Similarly the SHT21’s clock
input i.e. SCL is connected to pin 15 (GPIO 3/SCL) and this line also requires a 10kohm pull-up
resistor. The power supply requirements are also important. The power supply requirements for the
wireless temperature and humidity system are as follows:
SHT21: VDD (2.1V – 3.6V). For this application VDD is 2.8V
TELRAN Radio Frequency Module (RFM): Vchip (1.08-1.5V) and VDDIO (same digital I/O voltage
of the circuit interfaced to TELRAN. For the wireless temperature and humidity application VDD is
8V hence the RFM’s VDDIO is also 2.8V)
An example application is shown in Figure 4 using a single CR2032, 3V button cell and two voltage
regulators to provide all the voltages required by the wireless temperature and humidity system.
Alternatively a 1.5V button cell and a 3V boost circuit can also be used however the component
count would be higher.
For enhanced noise immunity and to ensure satisfactory performance, all the power supplies should
be decoupled using correct values of decoupling capacitors as specified in the schematics of Figure
4. Capacitors C1, C2, C3, C4 and C5 should be fitted and mounted close to the MCP1702
regulators while capacitor C6 should be mounted close to the TELRAN RFM.
Another important consideration is to ensure that the SHT21’s signal lines notably the SDA and
SCL lines are not routed close to regions of a circuit that are prone to noise as noise on the SDA
and SCL lines can lead to unreliable and unpredictable results. The regions to avoid include power
sections (especially those with switched-mode power supplies), or close to regions containing
oscillators or clock signals. The SHT21 is a highly integrated multi-sensor module incorporating a
capacitive-type humidity sensor and a band gap temperature sensor with a calibrated digital output
hence adequate space (>2cm) should also be maintained between the TELRAN RFM and the
SHT21 sensor to avoid interference between these devices.
connected freedom
TZ1053AN-06 Page 3
Expected Performance
The wireless temperature and humidity sensor is designed using the factory calibrated SensirionÔ
SHT21 temperature and humidity sensor. The SHT21 is a highly integrated multi-sensor module
incorporating a capacitive-type humidity sensor and a band gap temperature sensor with a
calibrated digital output. The TELRAN-based wireless temperature and humidity sensor is expected
to measure temperature in the range of 0°C to +70°C with temperature accuracy of +/-0.5°C max
where the sensor is co-located with TELRAN. It is also expected to measure relative humidity in the
range of 0 to 100% with a typical relative humidity accuracy of +/-3% max within the range 20 to
80% RH, see SHT21 datasheet for details. Where the sensor is remote from the TELRAN the
system can measure temperatures in the range -40°C to +120°C. For other temperature ranges
please contact Toumaz.
Power Consumption and example battery life calculation
The wireless system shown in Fig 1 and
Figure 4 uses standard components such as the MCP1702 low dropout (LDO) voltage regulator.
The peak total current consumption of the system is typically 4.3mA at 2.8V representing a peak
power consumption of 12mW when the system is in continuous operation. Of the 4.3mA, 3.3mA is
consumed by the TELRAN RFM when transmitting data to the TELRAN USB Dongle attached to the
PC. Furthermore, the SHT21 sensor operates at 3V with typical current consumption of 300μA
(during measurements) giving a total power consumption of 0.9mW. After a measurement the
SHT21 automatically switches back to sleep mode with a typical current consumption of 0.15uA and
waits for the next I2C command. The total power consumption of the system can therefore be
significantly reduced by local buffering of data on the TELRAN RFM and duty cycling the
transmission of data from the RFM to the TELRAN Dongle. The TELRAN RFM module is rated at
2.9mA in receive mode and 3.3mA in transmit mode.
[attachment=22228]
Introduction
This application note describes the design of a wireless temperature and relative humidity system
based on the TZ1053 TELRAN chip. The TELRAN chip is an ultra low power RF chip operating in
the license free ISM bands (EU 862MHz – 870MHz, USA 902MHz – 928MHz; Japan: 950MHz –
956MHz and China: 779-787MHz). An example design of a wireless temperature and humidity
system is shown (Fig 1) using the SHT21 temperature and humidity sensor from SensirionÔ
Such systems can be used in homes and offices for temperature and humidity
monitoring. They also find uses in automobiles, air conditioning systems and for remote temperature
and humidity monitoring in industry. A schematic of the system is shown in Figure 4. This schematic
shows the wireless temperature and humidity system made up of an SHT21 sensor interfaced to the
TELRAN chip via I2C interface.
Wireless Temperature
and Humidity Sensor Using TELRAN
Application note TZ1053AN-06 Oct 2011
Abstract Dr. C. Uche
This application note describes the complete system design (hardware and software) of a wireless
temperature and humidity monitoring system based on the TZ1053 ultra-low power wireless
TELRAN chip. The wireless temperature and humidity system can measure temperatures from 0°C
to +70°C where the sensor is co-located with TELRAN. The range for temperature can be extended
to -40°C to +120°C and for relative humidity 0 to 100% where the sensor is remote from TELRAN.
Design Considerations
Designing the TELRAN-based wireless temperature and humidity system involves interfacing the
TELRAN radio frequency module (RFM) to the SHT21 via I2C serial interface. As shown in the
design of Figure 4 the I2C data line i.e. SDA is connected to pin 14 (GPIO 2/SDA) input of the
TELRAN RFM. This connection requires a 10kohm pull-up resistor. Similarly the SHT21’s clock
input i.e. SCL is connected to pin 15 (GPIO 3/SCL) and this line also requires a 10kohm pull-up
resistor. The power supply requirements are also important. The power supply requirements for the
wireless temperature and humidity system are as follows:
SHT21: VDD (2.1V – 3.6V). For this application VDD is 2.8V
TELRAN Radio Frequency Module (RFM): Vchip (1.08-1.5V) and VDDIO (same digital I/O voltage
of the circuit interfaced to TELRAN. For the wireless temperature and humidity application VDD is
8V hence the RFM’s VDDIO is also 2.8V)
An example application is shown in Figure 4 using a single CR2032, 3V button cell and two voltage
regulators to provide all the voltages required by the wireless temperature and humidity system.
Alternatively a 1.5V button cell and a 3V boost circuit can also be used however the component
count would be higher.
For enhanced noise immunity and to ensure satisfactory performance, all the power supplies should
be decoupled using correct values of decoupling capacitors as specified in the schematics of Figure
4. Capacitors C1, C2, C3, C4 and C5 should be fitted and mounted close to the MCP1702
regulators while capacitor C6 should be mounted close to the TELRAN RFM.
Another important consideration is to ensure that the SHT21’s signal lines notably the SDA and
SCL lines are not routed close to regions of a circuit that are prone to noise as noise on the SDA
and SCL lines can lead to unreliable and unpredictable results. The regions to avoid include power
sections (especially those with switched-mode power supplies), or close to regions containing
oscillators or clock signals. The SHT21 is a highly integrated multi-sensor module incorporating a
capacitive-type humidity sensor and a band gap temperature sensor with a calibrated digital output
hence adequate space (>2cm) should also be maintained between the TELRAN RFM and the
SHT21 sensor to avoid interference between these devices.
connected freedom
TZ1053AN-06 Page 3
Expected Performance
The wireless temperature and humidity sensor is designed using the factory calibrated SensirionÔ
SHT21 temperature and humidity sensor. The SHT21 is a highly integrated multi-sensor module
incorporating a capacitive-type humidity sensor and a band gap temperature sensor with a
calibrated digital output. The TELRAN-based wireless temperature and humidity sensor is expected
to measure temperature in the range of 0°C to +70°C with temperature accuracy of +/-0.5°C max
where the sensor is co-located with TELRAN. It is also expected to measure relative humidity in the
range of 0 to 100% with a typical relative humidity accuracy of +/-3% max within the range 20 to
80% RH, see SHT21 datasheet for details. Where the sensor is remote from the TELRAN the
system can measure temperatures in the range -40°C to +120°C. For other temperature ranges
please contact Toumaz.
Power Consumption and example battery life calculation
The wireless system shown in Fig 1 and
Figure 4 uses standard components such as the MCP1702 low dropout (LDO) voltage regulator.
The peak total current consumption of the system is typically 4.3mA at 2.8V representing a peak
power consumption of 12mW when the system is in continuous operation. Of the 4.3mA, 3.3mA is
consumed by the TELRAN RFM when transmitting data to the TELRAN USB Dongle attached to the
PC. Furthermore, the SHT21 sensor operates at 3V with typical current consumption of 300μA
(during measurements) giving a total power consumption of 0.9mW. After a measurement the
SHT21 automatically switches back to sleep mode with a typical current consumption of 0.15uA and
waits for the next I2C command. The total power consumption of the system can therefore be
significantly reduced by local buffering of data on the TELRAN RFM and duty cycling the
transmission of data from the RFM to the TELRAN Dongle. The TELRAN RFM module is rated at
2.9mA in receive mode and 3.3mA in transmit mode.