Application Note 313: CO2 sensor - Design concept for
Contents
1. APPLICATION NOTE 313 Green Smart Wireless enocean 1 Introduction The concentration of carbon dioxide CO2 in a room is an indicator for indoor air quality IAQ CO sensors are therefore used to measure indoor air quality in a building to perform demand based ventilation Sensors for this purpose operate in the range between 500 and 5000 ppm ppm parts per million e g 10000 ppm 1 The figure below shows a typical CO concentration in an office during the day 600 400 200 0 08 00 10 00 12 00 14 00 16 00 18 00 Figure 1 example of CO2 level in an office As shown in the table below a level of 800 to 1200 ppm inside a building is seen as well ventilated Achieving lower levels will result in additional energy usage e g by the van or heating cooling Achieving only higher levels might result e g in reduced concentration or well being of the people in the room CO concentration Physiological effects APPLICATION NOTE 313 Green Smart Wireless enocean CO SENSOR DESIGN CONCEPT FOR SOLAR POWERED CO SENSOR 1 1 Purpose In order to build an energy harvesting self powered sensor the main challenge is energy consumption Most of today s available CO sensors require by far too much energy to be operated in such a system However this document demonstrates a self powered CO sen sor using an energy optimized sensor from Gas Sensing Solutions see 11 in combina tion with a smar2. This works for an application where the chip is on the Same temperature than ambient without any power dissipation to falsify the result NOTE The STM300 module needs to be calibrated in order to use the internal chip temperature sensor APPLICATION NOTE 313 Green Smart Wireless enocean CO SENSOR DESIGN CONCEPT FOR SOLAR POWERED CO SENSOR 2 6 Energy monitoring charge level To monitor the energy consumption a charge level of the capacitors is calculated and trans ferred via radio The charge level is evaluated by measuring the voltage VDD on the sto rage capacitor The usable voltage from 2 4 V up to 4 5 V is scaled to 0 up to 100 Energy Storage 4 5V 100 2 4V 0 OV Figure 13 Charge level Apart from transmitting the charge level for diagnostic and energy evaluation purposes the value is also used to operate the system in a save operating area down to 20 Switch ing on the embedded sensor causes voltage dips during periods with higher current con sumption of up to 0 6 V These voltage dips might cause under voltage resets 2 7 Radio telegram The CO sensor sends the following telegram similar to the EEP A5 09 04 As first data field the charge level See Energy monitoring charge level is send instead of the rel humidity NOTE The current implementation does not comply to the EEP A5 09 04 specifica tion and needs modifications for an end product Offset Size Description Val
3. diode detector technology The sensor is optimized for battery powered application and has the following key features Low power consumption 3 5 mW in continuous operation Fast power up time Battery operated 3 3 V Auto calibration Standard digital output serial interface Optional humidity and temperature measurement available The COZIR carbon dioxide sensor is available in two ranges COZIR ambient with a 0 to 2 000 ppm range suitable for applications such as heating ventilation and air conditioning HVAC indoor air quality IAQ education and horticulture COZIR wide range with a 0 to 100 range suitable for process control applications such as diving industrial safety and automotive 2 4 CO2 measurement In a self powered application there is not enough energy available to permanently supply the embedded sensor Therefore a dynamic power concept is required to reduce the energy consumption After powering up of the embedded sensor it takes about 2 s till the sensor delivers the first measurement result on the serial interface During this 2 s the sensor has actually per formed 4 internal measurements used to calculate the first result The STM 300 enters deep sleep mode for this 2 s in order to reduce current consumption After the measurement result was received the sensor power supply is switched of and the result is send via radio Then the STM 300 enters deep sleep mode for e g 10 minutes APPL
4. time This data is stored in RAMO during deep sleep periods Structure of RAMO area typedef struct uint8 u8State used to store system state during deep sleep uint8 u8ChargeLevel used to store charge level during sleep ine le ul6MinCO2Level used for dynamic sensor calibration uint1l6 ul WakeupCnt used for dynamic sensor calibration tRam0 APPLICATION NOTE 313 Green Smart Wireless enocean To monitor the time simply the number of wakeups is counted After a defined time period the recalibration would be done by sending a F command see 5 to the embedded sensor 2 8 1 Using the F command recalibration The recalibration uses the difference between the lowest measured CO level during the timeframe assumed to be fresh air level to a known fresh air level of e g 450 ppm For instance if the lowest CO reading was 460 ppm than the STM 300 needs to send a F command F 460 450 r n to the sensor The following steps need to be handled m Ensure that the sensor is ready to receive commands wait at least 100 ms after power on Send the actual F command with the calibration values Wait till F command is executed and calibration data is stored inside the embedded sen sors EEROM memory This can be evaluated by waiting for the sensor to reply to the F command Sensor power ADIO7 WU l ADIO6 l Il 100ms delay 12 4ms 59ms Cal amp save to EE
5. ICATION NOTE 313 Green Smart Wireless enoceahn 3 Subtelegrams Transmitting CPU mode A WXIDIO Sensor power TX Wake0 ca 2s 4 measurements gt one result Figure 12 one measurement cycle One measurement cycle 1 STM 300 module wakes up from deep sleep mode after the preset time Watchdog Timer Reset STM 300 turns on sensor power set WXIDIO to high STM 300 enables wakeup on sensor TX line and sets watchdog timer for sensor timeout 3 s in case no answer gt wakeup from sensor STM 300 enters deep sleep mode to wait for sensor result or timeout 5 Sensor performs CO measurement actually 4 single measurements are made in ternally After about 2 s the result is output on the serial port TX line Z 00879 z 00875 r n 6 The first falling edge on the TX line generates a falling edge on the WAKEO pin wak ing up the STM 300 module 7 The STM 300 module starts from reset enables the uart and receives the remaining characters on the serial line first lt space gt is lost and turns of the sensor power off as soon as it has received the necessary first characters Z 00879 STM 300 converts the value and sends the information via radio STM 300 sets the watchdog timer to 10 minutes and enters deep sleep mode with WAKEO wakeups disabled 2 5 Chip temperature sensor The demonstration utilizes the possibility to use the internal chip temperature sensor for measuring ambient temperature
6. PROM F repl e g _F_460_450 r n e g F 33124 i P cmd Figure 15 F command recalibration NOTE The actual implementation does not wait for the reply and simply waits 100 ms and then turns the sensor supply off 2 9 Some energy considerations Evaluating energy consumption has shown that the used solar cell provides enough energy to operate the sensor To maintain a steady state condition amount of energy provided by the solar cell amount of energy used by the application about 180 lux waking up every 10 minutes are needed This are about 16 6 uA 600 s 10000 uAs during a 10 minutes interval Figure 15 shows how the energy is consumed between the different functional blocks The most energy is related to the CO measurement about 60 is used by the embedded sen sor for the measurement powered for 2 s An additional 40 are caused by the DC DC converter supply current and the converting efficiency APPLICATION NOTE 313 Green Smart Wireless enocean m STM300 E tx E Sensor m DC DC converter MAX1595 E efficiency Figure 15 Energy consumption 3 Outlook Limitations The demonstration proves the feasibility of a solar powered wireless CO sensor but is not optimized for energy management e g will not survive the night no recharging To con vert this demonstration to a final product still some effort needs to be spent Some of the things that need to be cons
7. ae re en A E AN 9 2 4 COZ Measurement icttaniitunsindaeortintitonaiaciaortiadreentaiadtionhiacatanaiacreortieduiananeanaonaanes 9 2 5 Chip temperature SENSO saseteacamsmarsnuniaaneanwenoceneategeiapuancanemendeaeemnaninenen oneness 10 2 6 Energy monitoring Charge level c cece eeeeeeeeee eee e eee e eee eeeeeeeaeeeneeennnees 11 2 7 Radio telegram sisatetziacatadetasateiniasotsdctenstsdeiaendsdctaredsdadasedsd tavadadeiasntadtanadstnias 11 2 8 Embedded CO sensor recalibration cccccececeeeeueeeeeeeeuuueeeuueeeueveneuueneuueeeuunenas 12 2 8 1 Using the F command recalibration ssssssssssrsnrsrnnnsrrnnnrrnnrnrnrenrerenrenne 13 2 9 Some energy considerationS ssssssssssssssrrsrrsrrnnrnnsnnrnnrnnrnnrnnrnnrunrnnrnnrnnrunnne 13 S3 Outlook Limita OlS eier N E Ea 14 APPLICATION NOTE 313 Green Smart Wireless enocean 1 3 References Further details can be found in the following documentation 1 2 3 4 5 6 DolphinAPI user manual EO3000I_API chm 2 2 1 0 STM 300 user manual V1 25 December 3 2010 EnOcean Equipment Profiles EEP 2 1 20 Jun 2011 COZIR data sheet GSS COZIR Data Sheet pdf Rev B10 10 COZIR software user s guide COZIR Software User s Guide AL12 RevA pdf MAX1595 step up step down charge pump data sheet Rev 2 Useful web sites 7 8 9 10 11 12 EnOcean website http www enocean com EnOcean Alliance website ht
8. id range Scale Unit 08 Charge level linear 0 5 0 200 0 100 88 CO2 concentration linear 10ppm 0 255 0 2550 29 1i Humidity valid 0 not valid ae The figure below shows the actual EEP A5 09 04 profile as reference aaa M _ EnOcean www enocean com Subject to modifications Wolfgang Bihlmayr June 2011 Page 11 14 APPLICATION NOTE 313 RORG 4B5 Telegram pile 09 Gas Sensor _ ini o4 CO2 Sensor Rel Humidity linear 0 5 1 bit Concentration linear 10 ppm 1 bit Temperature linear 0 2 C 1 bit Not Used 0 Figure 14 EEP A5 09 04 2 8 Embedded CO gt sensor recalibration Green Smart Wireless enocean l0 255 0 51 0 Teach in telegram Data telegram Humidity Sensor not available Humidity Sensor available Temperature Sensor not available Temperature Sensor available The embedded CO sensor requires a recalibration from time to time due to effects e g caused by dust or dirt in the optics The method for recalibration assumes that during a longer timeframe of e g 2 3 weeks the sensor will at least measure once a fresh air CO gt level In applications where the embedded sensor is permanently supplied it automatically per forms this recalibration In the self powered system the STM functionality 300 needs to take care of this For the recalibration the STM 300 needs to monitor the lowest measured CO level in a given timeframe and the
9. idered in more detail are m required measurement rate m maybe dynamic adopting measurement rate to available energy charge level or day night time reduce measurement rate during night time or when room is dark m size of solar cell and capacitors m need for long term and short term storage including charge management m synchronization to uart communication after wakeup see 2 4 This is currently per formed by enabling the uart uart_init at fixed time after the wakeup It has not been evaluated tested if this will work under all circumstances An optional approach could be to monitor the first bit changes on the TX line and to enable the uart on detection of a specific bit pattern
10. l 2 x 0 22 F super caps NEC TOKIN FCOH224ZTBR24 are used For the demonstration the super caps were selected with a high capacitance combined with the capability to provide some mA required in order to pro vide the current needed by the STM 300 and embedded CO sensor Solar and caps MS GND VOUT SOLAR ECS31 Q 22F 5 5U Q 22F 5 5U C L Figure 5 Solar cell and storage capacitors APPLICATION NOTE 313 Green Smart Wireless enocean Figure 6 STM 300 As the embedded CO sensor requires a fixed 3 3 V VDD2 supply voltage a DC DC con verter is used to derive this voltage from VDD The MAX1595 charge pump regulator gene rates 3 3 V from a 1 8 V to 5 5 V input The solar cell generated VDD operating can vary from 1 8 V up to 5 5 V during operation Two MOSFETs enable to turn off the sensor supply for energy consumption reasons Using the WXIDIO pin for the control which is also sup plied during deep sleep allows supply the sensor even if the STM 300 is in deep sleep mode The other pins ADIOO 7 SCSEDIOO SCLKDIO1 WSDADIO2 RSDADIO3 are not powered in deep sleep mode and can t be used for this purpose sensor supply DC DC A4 UDO2 BSH2405 C4 flu As WxXIDIO BSH1 5 GNO R10 nap uon GNO Figure 7 sensor supply DC DC As already mentioned before special care is needed on the electrical interface between po wered and not powered parts of the sys
11. t measuring concept based on EnOcean s STM 300 radio module i URII gt ID V p mea sosriocosos me oe 0060 IEE ya os HEX Se Nee Nee eee ee N thd y IE J y 4 ly i gt Y JE Figure 2 Solar powered CO2 sensor This application note describes the principles how to built such a self powered CO sensor and is intended as basis for own developments It does not reflect a ready to use reference design The respective software is also available for download from the EnOcean website NOTE The software AN313SW which is part of this application note is provided on an AS IS basis EnOcean www enocean com Subject to modifications Wolfgang Bihlmayr June 2011 Page 2 14 APPLICATION NOTE 313 Green Smart Wireless enocealy 1 2 Table of content L TAEPOGIN CUO sci cetatacatenededsseeetncatamecadosateadscacccadpsahatadedanntedecatotadatamndndegacod deeacadadeeaees 1 1 1 PUDO cietatodadentteiatecsradidecsvanitodulec toni yadetedaledstraitedatadateauueustanwadiladstnestouaheuas 2 tI Ol CONMLOM ss Snostnssace deen tacacauensen EEE EE EENE 3 1 3 ROTOR CSS a acsantraanyaauiaaarasttaeayaasianavaueraanvaautaauraaeraunvaaniqaurnaerganvaceiqaurreeranracsiat 4 Z PENON TO a E nna E RUE E 4 2 1 System OvervieW sau acactcceccanatenense ce araceeicuagecdeci aces ten dcsceu aneneeelenaguedececcunecendaccee 5 2 2 SCHEMA ssnipe E ten eedeec etwas een eedeecetween ten eceeceteeen tenes 6 2 3 Empedded COs coq 0
12. tem For instance it s not allowed to apply any vol tage on the ADIO6 pin diode D1 during deep sleep mode see 2 2 3 1 GPIO supply vol tage APPLICATION NOTE 313 Green Smart Wireless enocean Sensor interface VUDD2 IOUDD_1U8 112 LAK e or iS zeae B u105 JP1 COZIRSENSOR 2 GND 2 Doe EN IAKEG gt D2 lx 71 1N4148 D1 PT 1N4148 Supply must be gt 3 3 IOVDD_1VU8 To Ak Figure 8 Sensor interface To program the STM 300 in system a connector to the EOP 300 programmer is foreseen The EOP 300 needs to be operated with 3 3 V The R7 and R8 O Ohm resistors are optional for debugging purposes to gain access to serial port Programming connector HII Supply must be 3 3Un LBN button C r E ET SCSEDIOG ee ele KSC2x1 J GNO GND Figure 10 LRN button ADIOS ADIOL ADIOZ ADIOS ADIO4 ADIOS ADIOS ADIOZ HXODIO S2 WXIDIO RX WAKES TX WAKE1 AOUT NZERO FAZERO VDD GND COZIR IN JP2 it 225 S cxn ah ze rrol RBEEXN Foce dAn me F MAX1S95EUA O bt i i i fi I O GND GND GND SOLAR 70uF Sour ff o Ts T T Figure 11 DEMO Implementation example APPLICATION NOTE 313 Green Smart Wireless enocean 2 3 Embedded CO gt sensor The COZIR ultra low power carbon dioxide sensor uses non dispersive infrared NDIR also see 9 configuration utilizing unique mid infrared light emitting diode source and photo
13. tp www enocean alliance org Wikipedia website http en wikipedia org wiki Nondispersive_infrared_sensor CO Sensor website http www cozir com Gas Sensing Solutions website http www gassensing co uk Maxim website http www maxim ic com 2 Demonstration The demonstrated system measures CO concentration ambient temperature chip tem perature and storage charge level every 10 min and transmits the data via radio In case of a poor charge level lt 20 the measurement and transmission in ceased until a higher charge level is reached Also an automatic long term calibration mechanism is implemented taking care of long term effects like dust or dirt in the sensor Using an existing EnOcean equipment profile EEP A5 09 04 the humidity level represents the charge level Using DolphinView as receiver the system can be easily monitored with the EEP view window NOTE The current implementation does not comply with the EEP A5 09 04 specifi cation and needs modifications for an end product APPLICATION NOTE 313 Green Smart Wireless enocean EEP View O Export Profiles eep 1 xml GReload XML Chart time resolution 6 hours EnOQcean Equipment Profile RORG Ox45 465 Telegram FUNC Ox09 Gas Sensor TYPE Ox04 CO2 Sensor Learn Telegram Time 2011 3 31 11 52 53 535 EEP 45 09 04 Manufacturer EnOcean GmbH 008 Data Telegram Interpretation y LRN Bit Data telegram H
14. umidity 72 00 13 33 40 14 50 00 15 46 20 a Concentration 890 00 ppm 13 53 40 14 50 00 13 46 20 A Temperature 23 00 C 13 33 40 14 50 00 15 46 20 I H Sensor Humidity Sensor not available I T Sensor Temperature Sensor available Figure 3 DolphinView EEP View 2 1 System overview The block diagram below shows the functional blocks of the self powered CO sensor sys tem The energy provided by the solar cell is stored in a long term storage capacitor Super cap supplying the system with its operating voltage The power supply of the embedded CO sensor is controlled from the STM 300 via the WXIDIO pin allowing switching off the embedded sensor during sleep times The embedded sensor needs a constant 3 3 V operat ing voltage generated by a step up step down charge pump DC DC converter APPLICATION NOTE 313 Green Smart Wireless enocean DC DC WXIDIO ADIO6 gt VDD Long Term Storage STM300 co2 Dolphin Chip Sensor Figure 4 Block diagram CO2 sensor As can be seen in the Schematics chapter special care is required on the interface between powered and not powered components in particular between embedded sensor and STM 300 e g ADIO6 ADIO7 2 2 Schematics The demonstration is based on a solar cell similar bigger size to the ECS 300 310 with the following parameters 67 0 x 28 0 x 1 1 mm e For the storage of the energy provided by the solar cel
Download Pdf Manuals
Related Search