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Cloud support module for the low-cost LoRa gateway

Description

clouds.json contains a list of clouds where you want your data to be uploaded. Here is an example with 5 clouds: local MongoDB, WAZIUP (based on FiWare), ThingSpeak, MQTT (with test.mosquitto.org broker) and GroveStreams.

{
	"clouds" : [
		{	
			"name":"Local gateway MongoDB",			
			"notice":"do not remove the MongoDB cloud declaration, just change enabled and max_months_to_store if needed"
			"script":"python CloudMongoDB.py",
			"type":"database",
			"max_months_to_store":2,
			"enabled":false
		},
			"name":"WAZIUP Orion cloud new API",
			"script":"python CloudWAZIUP.py",
			"type":"iotcloud",
			"enabled":true
		},				
		{	
			"name":"ThingSpeak cloud",
			"script":"python CloudThingSpeak.py",
			"type":"iotcloud",			
			"enabled":true
		},
		{	
			"name":"MQTT cloud",
			"script":"python CloudMQTT.py",
			"type":"MQTT",			
			"enabled":false
		},				
		{	
			"name":"GroveStreams cloud",
			"script":"python CloudGroveStreams.py",
			"type":"iotcloud",			
			"enabled":true
		}
}

Note that storage on the local MongoDB is declared as a cloud, among others that you can declare. You should not remove this cloud declaration and leave it in first position even if position has no real matter. clouds.json is parsed by post_processing_gw.py using clouds_parser.py. For each cloud declaration, there are only 2 relevant fields: script and enabled. script is used for you to provide the name of a script. You have also to indicate which launcher will be used. In this way, you can use several script languages (including shell scripts or executables provided that they read parameters that are passed by their command line). For instance, if the script is a python script, enter python my_script_filename. enabled set to true indicates that you want this cloud to be active so thatpost_processing_gw.py will call the associated script to perform upload of the received data. All the other fields are not relevant for post_processing_gw.py but can be used by the associated script to get additional information that you may want to provide through the clouds.json file. Otherwise, you can always provide these additional information statically in the script.

Recall that a message will be upload to cloud only if it is prefixed with \!. So assuming that you are sending \!#4#TC/21.5 (the data format will be explained in following paragraphs) post_processing_gw.py provides 5 parameters to your script when it is launched.

  • ldata: the received data (without the prefix)
    • e.g. #4#TC/21.5 as 1t argument (sys.argv[1] in python)
  • pdata: packet information
    • e.g. 1,16,3,0,10,8,-45 as 2nd argument (sys.argv[2] in python)
    • interpreted as dst, ptype, src, seq, len, SNR, RSSI for the last received packet
  • rdata: the LoRa radio information
    • e.g. 500,5,12 as 3rd argument (sys.argv[3] in python)
    • interpreted as bw, cr, sf for the last received packet
  • tdata: the timestamp information
    • e.g. 2016-10-04T02:03:28.783385 as 4th argument (sys.argv[4] in python)
  • gwid: the gateway id
    • e.g. 00000027EBBEDA21 as 5th argument (sys.argv[5] in python)

These parameters are passed to the script and it is up to the cloud script to use these parameters or not. The main structure of a Python cloud script to handle a particular cloud can therefore be summarized as follows:

IMPORT-AS-MANY-PACKAGES-AS-YOU-NEED
DEFINE-AS-MANY-FUNCTIONS-AS-YOU-NEED

def main(ldata, pdata, rdata, tdata, gwid):
	arr = map(int,pdata.split(','))
	dst=arr[0]
	ptype=arr[1]				
	src=arr[2]
	seq=arr[3]
	datalen=arr[4]
	SNR=arr[5]
	RSSI=arr[6]
	
	arr = map(int,rdata.split(','))
	bw=arr[0]
	cr=arr[1]
	sf=arr[2]
	
	DO-WHATEVER-YOU-NEED-TO-DO-FOR-DATA-UPLOADING
	
	USE-PARAMETERS-AS-YOU-NEED
		
if __name__ == "__main__":
	main(sys.argv[1], sys.argv[2], sys.argv[3], sys.argv[4], sys.argv[5])

This cloud design approach allows for:

  • a very generic post_processing_gw.py script that handles the interface with the low-level lora_gateway program
  • the end-user to have the entire responsability (through a cloud script) to decode the raw data provided by the end-device

Assuming that _enabled_clouds contains:

['python CloudThingSpeak.py', 'python CloudGroveStreams.py']

The main data upload processing task in post_processing_gw.py is very simple and looks like:

ldata = getAllLine()
print "number of enabled clouds is %d" % len(_enabled_clouds)	

#loop over all enabled clouds to upload data
#once again, it is up to the corresponding cloud script to handle the data format
#
for cloud_index in range(0,len(_enabled_clouds)):
	print "--> cloud[%d]" % cloud_index
	cloud_script=_enabled_clouds[cloud_index]
	print "uploading with "+cloud_script
	cmd_arg=cloud_script+" \""+ldata+"\""+" \""+pdata+"\""+" \""+rdata+"\""+" \""+tdata+"\""+" \""+_gwid+"\""
	os.system(cmd_arg) 
print "--> cloud end"

Good practice for storing keys or identification information

Most of cloud platforms use some kind of keys for write access. These keys should be stored in a separate Python file so that updates on the cloud script can be realized independently from the existing keys (for instance if you already customized from a previous install). In the provided examples, key_FireBase.py, key_GroveStreams.py and key_ThingSpeak.py contain keys for their corresponding clouds. For instance, CloudThingSpeak.py starts with an import key_ThingSpeak statement. Only key_ThingSpeak.py has a usable key, which is our LoRa demo channel write key: SGSH52UGPVAUYG3S.

> cat key_ThingSpeak.py
# LoRa demo channel
_def_thingspeak_channel_key='SGSH52UGPVAUYG3S'

For the other clouds, you have to create your own account in order to get your private key before being able to upload data to FireBase or GroveStreams.

Indicate a list of allowed source addresses and other advanced features

We also define in the key file a list of allowed device source address:

> cat key_ThingSpeak.py
# LoRa demo channel
_def_thingspeak_channel_key='SGSH52UGPVAUYG3S'
#Note how we can indicate a device source addr that are allowed to use the script
#Use decimal between 2-255 and use 4-byte hex format for LoRaWAN devAddr
#leave empty to allow all devices
#source_list=["3", "255", "01020304"]	
source_list=["3","10"]

When source_list is set to [] then all device are accepted. If it specifies a list of device address, then CloudThingSpeak.py will only upload data from these devices.

The code of CloudThingSpeak.py scripts looks like:

if (src_str in key_ThingSpeak.source_list) or (len(key_ThingSpeak.source_list)==0):

	DO-WHATEVER-YOU-NEED-TO-DO-FOR-DATA-UPLOADING
	
	USE-PARAMETERS-AS-YOU-NEED
else:
	print "Source is not is source list, not sending with CloudThingSpeak.py"

This feature is quite useful when you want to upload data to various different clouds, depending on the device. Suppose that you have 10 devices whose addresses are from 1 to 10. You want to upload data from sensors 1..5 to a ThingSpeak channel and data from sensors 6..10 to GroveStreams. Then you need to activate in clouds.json both clouds and specify in key_ThingSpeak.py source_list=["1","2","3","4","5"] and in key_GroveStreams.py source_list=["6","7","8","9","10"].

If you want to upload to 2 different ThingSpeak channels, you can do so by duplicating the CloudThingSpeak.py script into CloudThingSpeak_1.py, creating a new key_ThingSpeak_1.py file to store both the other ThingSpeak write key and source_list, changing in CloudThingSpeak_1.py the import key_ThingSpeak into import key_ThingSpeak_1 as key_ThingSpeak and then activating both CloudThingSpeak.py and CloudThingSpeak_1.py in clouds.json as follows:

{
	"clouds" : [
		{	
			"notice":"do not remove the MongoDB cloud declaration, just change enabled and max_months_to_store if needed"
			"name":"Local gateway MongoDB",
			"script":"python CloudMongoDB.py",
			"type":"database",
			"max_months_to_store":2,
			"enabled":false
		},	
		{	
			"name":"ThingSpeak cloud",
			"script":"python CloudThingSpeak.py",
			"type":"iotcloud",			
			"enabled":true
		},
			"name":"ThingSpeak cloud",
			"script":"python CloudThingSpeak_1.py",
			"type":"iotcloud",			
			"enabled":true
		}
}

However, as ThingSpeak is a simple and very popular IoT cloud, we enhanced CloudThingSpeak.py with many useful features such as: be able to assign a specific channel write key, a specific chart (field index) and a specific field offset (depending a nomenclature code) according to the sensor source address. In addition to _def_thingspeak_channel_key and source_list, key_ThingSpeak.py defines:

  • key_association
  • field_association
  • nomenclature_association

for instance:

  • key_association=[('AAAAAAAAAAAAAAAA', 9), ('BBBBBBBBBBBBBBBB', 10, 11)]
    • node 9 will use channel AAAAAAAAAAAAAAAA
    • node 10 and 11 will use channel BBBBBBBBBBBBBBBB
    • other nodes will use default channel
    • note that priority is given to key association defined on gateway
    • with key association you can go beyond the limitation of 8 charts per channel: if you have many sensors, you can assign specific channel's write key to specific sensors
  • field_association=[(6,1),(7,5)]
    • [(6,1),(7,5)] means data from respectively sensor 6/7 will use starting field index of 1/5
  • nomenclature_association=[("TC",0),("HU",1),("LU",2),("CO2",3)]
    • ("TC",0) means that if nomemclature is "TC" then the offset for field index will be 0

More details are given below.

Some words about data format

If several cloud systems is used, each with some specific features, then the raw data format can be complex and the decoding tasks of these data by the various scripts may need to be also more complex. This is exactely the case with our example templates where we want to be able to specify a particular write key and field when uploading to ThingSpeak and still be able to use the dynamic field creation feature of Grovestreams or WAZIUP Orion platform. For example, we want to be able to send various message formats such as:

  • SGSH52UGPVAUYG3S##22.5 or SGSH52UGPVAUYG3S#22.5 : specified a ThingSpeak write key with a the default field, value is 22.5
  • #4#22.5 or 4#22.5 : specified a field when using the default ThingSpeak write key, value is 22.5
  • SGSH52UGPVAUYG3S#4#22.5 : specified both a ThingSpeak write key and a field, value is 22.5
  • ##22.5 : use default value for both ThingSpeak write key and field
  • 22.5 : use default value for both ThingSpeak write key and field; or use default nomenclature (i.e. DEF) for Grovestreams and MongoDB
  • ##TC/22.5 : use the possibility to define a particular nomenclature with Grovestreams and MongoDB (e.g. TC for temperature in Celsius)
  • TC/22.5 : use the possibility to define a particular nomenclature with Grovestreams and MongoDB (e.g. TC for temperature in Celsius)
  • TC/22.5/HU/85/LU/78 : use the possibility to define multiple nomenclatures and values with Grovestreams and MongoDB

Even for ThingSpeak, we recommend now to use the following format example: TC/22.5/HU/24/LU/345/CO2/456.... Heere is a detailed example with CloudThingSpeak.py. Assuming that key_ThingSpeak.py contains:

_def_thingspeak_channel_key='SGSH52UGPVAUYG3S'
source_list=["6", "7", "8", "9"]
key_association=[('AAAAAAAAAAAAAAAA', 9), ('BBBBBBBBBBBBBBBB', 10, 11)]
field_association=[(6,1),(7,5)]
nomenclature_association=[("TC",0),("HU",1),("LU",2),("CO2",3)]

and assuming that each sensor node has 4 physical sensors: TC, HU, LU, CO2

  • if we receive "TC/22.5/HU/24/LU/345/CO2/456" from sensor 6
    • data will be accepted
    • starting field index for the channel will be 1
    • TC will be uploaded on field 1, HU on field 2, LU on field 3 and CO2 on field 4
  • if we receive only "HU/24/LU/345" from sensor 6 because these physical measures are sent at higher frequency
    • HU and LU will still be respectively uploaded on field 2 and 3
  • if we receive "TC/22.5/HU/24/LU/345/CO2/456" from sensor 7
    • data will be accepted
    • starting field index for the channel will be 5
    • TC will be uploaded on field 5, HU on field 6, LU on field 7 and CO2 on field 8
    • in this example, with 4 physical sensors per node, then a ThingSpeak channel can handle 2 nodes
  • if we receive "CCCCCCCCCCCCCCCC#TC/22.5/HU/24/LU/345/CO2/456" from sensor 8
    • data will be accepted
    • data will be uploaded on the channel which write key is "CCCCCCCCCCCCCCCC" as there is no key association defined
    • starting field index will be the default value, i.e. 1
    • TC will be uploaded on field 1, HU on field 2, LU on field 3 and CO2 on field 4
  • if we receive "CCCCCCCCCCCCCCCC#5#TC/22.5/HU/24/LU/345/CO2/456" from sensor 8
    • data will be accepted
    • data will be uploaded on the channel which write key is "CCCCCCCCCCCCCCCC"
    • starting field index will be 5
    • TC will be uploaded on field 5, HU on field 6, LU on field 7 and CO2 on field 8
  • if we receive "CCCCCCCCCCCCCCCC#TC/22.5/HU/24/LU/345/CO2/456" from sensor 9
    • data will be accepted
    • data will be uploaded on the channel which write key is "AAAAAAAAAAAAAAAA" as there is a key association that has priority
    • starting field index will be the default value, i.e. 1
    • TC will be uploaded on field 1, HU on field 2, LU on field 3 and CO2 on field 4
  • if we receive "TC/22.5/HU/24/AA/345/BB/456" from sensor 6
    • data will be accepted
    • starting field index for the channel will be 1
    • TC will be uploaded on field 1, HU on field 2, AA on field 3 and BB on field 4 even if AA and BB have no nomenclature association
  • if we receive "YY/30/TC/22.5/AA/345/BB/456" from sensor 6
    • data will be accepted
    • starting field index for the channel will be 1
    • YY will be uploaded on field 1, TC on field 1, AA on field 3 and BB on field 4. Here YY has no nomenclature association and you can see that TC overwrite YY on field 1
  • if we receive "TC/22.5/HU/24/LU/345/CO2/456" from sensor 10
    • data will be discarded by CloudThingSpeak.py

If you look at the provided example for ThingSpeak, Grovestreams and MongoDB clouds, you can see how we handle/decode/process these various data formats (by looking for delimiters) so that data from an end-device can sequentially be uploaded on various clouds platforms. For instance, # delimiters are not relevant for both Grovestreams and MongoDB (these cloud scripts will simply ignore them) while they are for ThingSpeak. If you only use one cloud platform then the data format and the cloud script can be much more simple.

Output examples

The LoRa gateway is usually started as follows:

> sudo ./lora_gateway --mode 1 | python post_processing_gw.py &

The post_processing_gw_py script will start by parsing the clouds declarations in clouds.json and adds a new cloud script for each enabled cloud.

Parsing cloud declarations
[u'python CloudThingSpeak.py']
[u'python CloudThingSpeak.py', u'python CloudGroveStreams.py']
Parsed all cloud declarations
post_processing_gw.py got cloud list: 
[u'python CloudThingSpeak.py', u'python CloudGroveStreams.py']	

When incoming data with \! prefix is processed, post_processing_gw.py will loop over all enabled clouds to call their respective script.

number of enabled clouds is 2
--> cloud[0]
uploading with python CloudThingSpeak.py
ThingSpeak: uploading
rcv msg to log (\!) on ThingSpeak ( default , 4 ): 21.5
ThingSpeak: will issue curl cmd
curl -s -k -X POST --data field4=21.5&field8=0 https://api.thingspeak.com/update?key=SGSH52UGPVAUYG3S
ThingSpeak: returned code from server is 156
--> cloud[1]
uploading with python CloudGroveStreams.py
GroveStreams: uploading
Grovestreams: Uploading feed to: /api/feed?compId=node_6&TC=21.5
--> cloud end

Remotely editing the clouds.json file

The gateway has a simple web admin interface that allows you to configure the ThingSpeak cloud and the WAZIUP Orion cloud (used by the WAZIUP european project). For all advanced editing of clouds.json file there are 2 possibilities. The first one is to use ssh to log into the gateway and then use the nano editor to edit the clouds.json file. Use CTRL-O+RETURN to save the file and then CTRL-X to quit.

> ssh pi@192.168.200.1
> cd lora_gateway
> nano clouds.json

Normally, if you have a recent SD card image, on ssh to the gateway, you will enter the simple command text interface. Then use option D to edit the clouds.json file.

=======================================* Gateway 00000027EBD4F300 *===
0- sudo python start_gw.py                                           +
1- sudo ./lora_gateway --mode 1                                      +
2- sudo ./lora_gateway --mode 1 | python post_processing_gw.py       +
3- ps aux | grep -e start_gw -e lora_gateway -e post_proc -e log_gw  +
4- tail --line=25 ../Dropbox/LoRa-test/post-processing.log           +
5- tail --line=25 -f ../Dropbox/LoRa-test/post-processing.log        +
6- less ../Dropbox/LoRa-test/post-processing.log                     +
------------------------------------------------------* Bluetooth *--+
a- run: sudo hciconfig hci0 piscan                                   +
b- run: sudo python rfcomm-server.py                                 +
c- run: nohup sudo python rfcomm-server.py -bg > rfcomm.log &        +
d- run: ps aux | grep rfcomm                                         +
e- run: tail -f rfcomm.log                                           +
---------------------------------------------------* Connectivity *--+
f- test: ping www.univ-pau.fr                                        +
--------------------------------------------------* Filtering msg *--+
l- List LoRa reception indications                                   +
m- List radio module reset indications                               +
n- List boot indications                                             +
o- List post-processing status                                       +
p- List low-level gateway status                                     +
--------------------------------------------------* Configuration *--+
A- show gateway_conf.json                                            +
B- edit gateway_conf.json                                            +
C- show clouds.json                                                  +
D- edit clouds.json                                                  +
---------------------------------------------------------* Update *--+
U- update to latest version on repository                            +
V- download and install a file                                       +
W- run a command                                                     +
-----------------------------------------------------------* kill *--+
K- kill all gateway related processes                                +
k- kill rfcomm-server process                                        +
R- reboot gateway                                                    +
S- shutdown gateway                                                  +
---------------------------------------------------------------------+
Q- quit                                                              +
======================================================================
Enter your choice: 
D
----------------------------------------------------------------------	

A second solution is to use a text editor on your computer/laptop that can directly edit and save a file on the Raspberry gateway. Nodepad++ on Windows and TextWrangler on MacOs do that quite nicely and they usually use FTP/SFTP feature. You can follow this tutorial http://trevorappleton.blogspot.fr/2014/03/remotely-modify-text-file-on-your.html or this one https://www.dirtyoptics.com/edit-files-on-your-raspberry-pi-the-easy-way/.

Support of MongoDB as a cloud declaration

As indicated previously, local storage of incoming data in the local MongoDB database is now viewed as a cloud upload. In the previous cloud declarations of clouds.json, if you enable the MongoDB cloud here is a typical output:

--> cloud[0]
uploading with python CloudMongoDB.py
MongoDB with max months to store is 2
MongoDB: removing obsolete entries
MongoDB: deleting data older than 2 month(s)...
MongoDB: 0 documents deleted
MongoDB: saving the document in the collection...
MongoDB: saving done

The local MongoDB database is structured as follows: the database is messages and the collection is ReceivedData. You can look at MongoDB.py for more details. CloudMongoDB.py is then the script that post_processing_gw.py will call to insert received data into the ReceivedData collection of messages database.

It is assumed that your data is formatted as follows, with a nomenclature code followed by the associated value:

TC/22.5/HU/85...

CloudMongoDB.py will create a json array with your received data as follows:

{ "TC":22.5, "HU":85 }

but will also add the SNR and the RSSI of the received radio messages to have the following json array:

{ "SNR":8, "RSSI": -56, "TC":22.5, "HU":85 } 

Then, the json document that will be inserted into the ReceivedData collection is as follows:

"type" : ptype,
"gateway_eui" : gwid, 
"node_eui" : src,
"snr" : SNR, 
"rssi" : RSSI, 
"cr" : cr, 
"datarate" : "SF"+str(sf)+"BW"+str(bw),
"time" : now,
"data" : json.dumps(json.loads(str_json_data))

A typical document would then be:

"type" : 18,
"gateway_eui" : "00000027EBBEDA21", 
"node_eui" : 10,
"snr" : 8, 
"rssi" : -56, 
"cr" : 5, 
"datarate" : "SF12BW125",
"time" : "2017-03-24T20:28:55.446Z",
"data" : { "SNR":8, "RSSI": -56, "TC":22.5, "HU":85 }

In the collection, the entry would look like:

{ "_id" : ObjectId("58d5818774fece07013e4f39"), "node_eui" : 10, "snr" : 8, "datarate" : "SF12BW125", "gateway_eui" : "00000027EBBEDA21", "rssi" : -56, "time" : ISODate("2017-03-24T20:28:55.446Z"), "type" : 18, "cr" : 5, "data" : "{\"SNR\": 8, \"RSSI\": -36, \"TC\": 22.5, \"HU\": 85}" }	

The local MongoDB database is directly linked with the embedded web server. Use a web browser to connect to the gateway (e.g. http://192.168.200.1) to graphically visualize the received data. The web server will show all available nomenclature codes (e.g. TC, HU, ...) as well as the SNR and RSSI as these values have been inserted into the data json array. You will be able to select which nomenclature you want to visualize as well as selecting a set of sensors.

You can also interact with the MongoDB database using the command line as follows:

pi@raspberrypi:~/lora_gateway $ mongo
MongoDB shell version: 2.4.10
connecting to: test
Server has startup warnings: 
Tue Jul 25 08:07:49.513 [initandlisten] 
Tue Jul 25 08:07:49.513 [initandlisten] ** NOTE: This is a 32 bit MongoDB binary.
Tue Jul 25 08:07:49.513 [initandlisten] **       32 bit builds are limited to less than 2GB of data (or less with --journal).
Tue Jul 25 08:07:49.513 [initandlisten] **       See http://dochub.mongodb.org/core/32bit
Tue Jul 25 08:07:49.513 [initandlisten] 
> show dbs
local	0.03125GB
messages	0.0625GB
> use messages
switched to db messages
> show collections
ReceivedData
system.indexes
> db.ReceivedData.find().pretty()
{
	"_id" : ObjectId("58d5718274fece0472bf60e5"),
	"node_eui" : 10,
	"snr" : 8,
	"datarate" : "SF12BW125",
	"gateway_eui" : "00000027EBBEDA21",
	"rssi" : -65,
	"time" : ISODate("2017-03-24T19:20:34.715Z"),
	"type" : 18,
	"cr" : 5,
	"data" : "{\"SNR\": 8, \"RSSI\": -65, \"SHU\": 1004}"
}
{
	"_id" : ObjectId("58d57fef74fece068e221277"),
	"node_eui" : 10,
	"snr" : 8,
	"datarate" : "SF12BW125",
	"gateway_eui" : "00000027EBBEDA21",
	"rssi" : -61,
	"time" : ISODate("2017-03-24T20:22:07.690Z"),
	"type" : 18,
	"cr" : 5,
	"data" : "{\"SNR\": 8, \"RSSI\": -61, \"SHU\": 991}"
}
{
	"_id" : ObjectId("58d580ae74fece069a795276"),
	"node_eui" : 10,
	"snr" : 8,
	"datarate" : "SF12BW125",
	"gateway_eui" : "00000027EBBEDA21",
	"rssi" : -66,
	"time" : ISODate("2017-03-24T20:25:18.439Z"),
	"type" : 18,
	"cr" : 5,
	"data" : "{\"SNR\": 8, \"RSSI\": -66, \"SHU\": 993}"
}
...

You can list all data from sensor 10 with:

> db.ReceivedData.find({node_eui:10})
{ "_id" : ObjectId("58d5718274fece0472bf60e5"), "node_eui" : 10, "snr" : 8, "datarate" : "SF12BW125", "gateway_eui" : "00000027EBBEDA21", "rssi" : -65, "time" : ISODate("2017-03-24T19:20:34.715Z"), "type" : 18, "cr" : 5, "data" : "{\"SNR\": 8, \"RSSI\": -65, \"SHU\": 1004}" }
{ "_id" : ObjectId("58d57fef74fece068e221277"), "node_eui" : 10, "snr" : 8, "datarate" : "SF12BW125", "gateway_eui" : "00000027EBBEDA21", "rssi" : -61, "time" : ISODate("2017-03-24T20:22:07.690Z"), "type" : 18, "cr" : 5, "data" : "{\"SNR\": 8, \"RSSI\": -61, \"SHU\": 991}" }
{ "_id" : ObjectId("58d580ae74fece069a795276"), "node_eui" : 10, "snr" : 8, "datarate" : "SF12BW125", "gateway_eui" : "00000027EBBEDA21", "rssi" : -66, "time" : ISODate("2017-03-24T20:25:18.439Z"), "type" : 18, "cr" : 5, "data" : "{\"SNR\": 8, \"RSSI\": -66, \"SHU\": 993}" }

If you want to delete all entries of the ReceivedData collection, you can issue the following command:

> db.ReceivedData.remove({})

Enjoy! C. Pham