Need help to select the best parts for BS2 sensor node project
PeteStarks
Posts: 7
Goal: To build a compact sensor node that will monitor Light levels, Temperature and Humidity while being both accurate and low cost. Nodes will be installed at a distance of 20ft-45ft and preferably connect via CAT5 cable to the controller. To aid in speedy development and avoid dead ends sensors should have existing code for the Basic Stamp 2.
Notes: This is in no way a definitive guide to all of these sensors. I will be summarizing each component based on information from various sources I stumble across, if you see a mistake please point it out.
Sensors:
Light Levels-
I believe this will be the simplest sensor of them all. I do not require it to be very accurate, Im only trying to detect if the lights are either on or off for the most part. I believe a basic RC time circuit and phototransistor as described in the WAM book wil accomplish this.
Temperature:
LM34 with ADC-
Total Cost: ~$6-$10
Pros: Thanks to some help on this forum I was able to get this sensor working with an accuracy of
~1-1.5F(based on the reading of my laser thermometer). It is very simple to connect to the BS2 and well tested in many projects and devices.
Cons: Being an analog sensor and requiring an ADC IC adds cost adds another layer of complexity to the node.
DS1620-
Total Cost: - ~$6
Pros: Accurate to +/- 0.5C, lower cost than the LM34 and ADC unless buying in bulk. Has an added bonus of being able to program actions for HI and Low temps.
Cons: Is a 3-wire component and as stated by Mike Green (http://forums.parallax.com/showthread.php/112343), It seems this would not meet my requirement of being 20-40 feet away from the BS2.
Humidity:
HS1101 Humidity Sensor-
Total Cost: ~$10
Pros: Said to be very accurate based on calibration with use of a 555 timer circuit. I do not have this component to currently test with, but based on forum posts it sounds like it would fit my distance requirement.
Con: Like the LM34 this sensor requires addition components to meet my needs. It is also not very well documented at the distance I planned to use it for based on my limited research.
Combo Temp/Humidity:
Parallax Sensirion Temperature/Humidity Sensor(item 28018)-
Total Cost: ~$43
Pros: I own and have used one of these sensors in various projects before with great success. The humidity accuracy of +/- 3.5% worries me a little, however the ease of use and feature set makes it a solid option for the node. There have been posts of people using this sensor at about 40ft which meets my needs perfectly.
Cons: Cost and +/- 3.5% accuracy
DHT22-
Total Cost: $5-$13(China vs USA)
Data Sheet: http://www.adafruit.com/datasheets/DHT22.pdf
Pros: Data sheet claims accuracy of +/- 0.5% and a transmission distance of ~65ft(20m).
Cons: Not much chatter about these sensors on the forum. The closest code sample I found was a Propeller Object for the DHT21. These sensors are very popular with the Arduino crowd, but have not seemed to have caught on at all with the BS2. There were also claims that the humidity readings were not as accurate as the sheet says.
Various Sensirion sensors:
Total cost: $10-$25(ebay, various sources)
Data Sheets: (SHT71) http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_SHT7x_Datasheet_V5.pdf
(SHT21) https://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf
Pros: Greater range of accuracy, with the SHT21 being +/-1% and the SHT71 being +/- 3% at a lower price point. Sensirion sensors have been used in many projects and are well documented as being reliable.
Cons: Most low cost version of this sensor would require some form of breakout board as they are extremely small. The SH71 seems to be a good candidate, but I have not fully researched what it would take to pull data from it with the BS2 vs using the SHT1x sensors.
Please recommend any other sensors that you believe would fit my needs. Any corrections or additions to my pros and cons for the sensors I have listed are welcomed as well. I hope to find the lowest cost solution for these nodes, however I feel the SHT1x available here will be a suitable fall back. It would just drive my per node cost up to a level Im attempting to avoid.
Notes: This is in no way a definitive guide to all of these sensors. I will be summarizing each component based on information from various sources I stumble across, if you see a mistake please point it out.
Sensors:
Light Levels-
I believe this will be the simplest sensor of them all. I do not require it to be very accurate, Im only trying to detect if the lights are either on or off for the most part. I believe a basic RC time circuit and phototransistor as described in the WAM book wil accomplish this.
Temperature:
LM34 with ADC-
Total Cost: ~$6-$10
Pros: Thanks to some help on this forum I was able to get this sensor working with an accuracy of
~1-1.5F(based on the reading of my laser thermometer). It is very simple to connect to the BS2 and well tested in many projects and devices.
Cons: Being an analog sensor and requiring an ADC IC adds cost adds another layer of complexity to the node.
DS1620-
Total Cost: - ~$6
Pros: Accurate to +/- 0.5C, lower cost than the LM34 and ADC unless buying in bulk. Has an added bonus of being able to program actions for HI and Low temps.
Cons: Is a 3-wire component and as stated by Mike Green (http://forums.parallax.com/showthread.php/112343), It seems this would not meet my requirement of being 20-40 feet away from the BS2.
Humidity:
HS1101 Humidity Sensor-
Total Cost: ~$10
Pros: Said to be very accurate based on calibration with use of a 555 timer circuit. I do not have this component to currently test with, but based on forum posts it sounds like it would fit my distance requirement.
Con: Like the LM34 this sensor requires addition components to meet my needs. It is also not very well documented at the distance I planned to use it for based on my limited research.
Combo Temp/Humidity:
Parallax Sensirion Temperature/Humidity Sensor(item 28018)-
Total Cost: ~$43
Pros: I own and have used one of these sensors in various projects before with great success. The humidity accuracy of +/- 3.5% worries me a little, however the ease of use and feature set makes it a solid option for the node. There have been posts of people using this sensor at about 40ft which meets my needs perfectly.
Cons: Cost and +/- 3.5% accuracy
DHT22-
Total Cost: $5-$13(China vs USA)
Data Sheet: http://www.adafruit.com/datasheets/DHT22.pdf
Pros: Data sheet claims accuracy of +/- 0.5% and a transmission distance of ~65ft(20m).
Cons: Not much chatter about these sensors on the forum. The closest code sample I found was a Propeller Object for the DHT21. These sensors are very popular with the Arduino crowd, but have not seemed to have caught on at all with the BS2. There were also claims that the humidity readings were not as accurate as the sheet says.
Various Sensirion sensors:
Total cost: $10-$25(ebay, various sources)
Data Sheets: (SHT71) http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_SHT7x_Datasheet_V5.pdf
(SHT21) https://www.sparkfun.com/datasheets/Sensors/SHT1x_datasheet.pdf
Pros: Greater range of accuracy, with the SHT21 being +/-1% and the SHT71 being +/- 3% at a lower price point. Sensirion sensors have been used in many projects and are well documented as being reliable.
Cons: Most low cost version of this sensor would require some form of breakout board as they are extremely small. The SH71 seems to be a good candidate, but I have not fully researched what it would take to pull data from it with the BS2 vs using the SHT1x sensors.
Please recommend any other sensors that you believe would fit my needs. Any corrections or additions to my pros and cons for the sensors I have listed are welcomed as well. I hope to find the lowest cost solution for these nodes, however I feel the SHT1x available here will be a suitable fall back. It would just drive my per node cost up to a level Im attempting to avoid.