HC Bluetooth module - quick notes

A while ago I bought a cheap Bluetooth module off ebay and for some reason, I always thought it is a HC-05 module: not only that this is what the ebay page said but also because a long time ago when I tried Amarino on my phone, it connected to the Bluetooth module and its name was HC-05. It works great with Amarino and my custom sketches but only at 9600 which seems to be the default (most people on the web say the default is a higher baud rate but I discovered this being my case by trying different settings in a test sketch) but Firmata needs 57600 (in my opinion, both BT module and Firmata sketch set at 9600 should work fine but I tried and for some reason it doesn't).

Thinking I have a HC-05 I tried to change its default speed to 57600 by following this instructables - my module didn't have a wire on the KEY pin so I soldered one. However, after all connection were done and I ran the sketch, I noticed that no commands worked with one exception "AT+NAME=MYBLUE" - it was the only command that received a response from the module, "OKsetname". To check if something changed, I paired the module with my phone and to my surprise the name was "=MYBLUE" not just MYBLUE so something was not quite right.

Digging more on the web, found another instructables. The module I have doesn't have the same markings on the back (mine says V1.04) and it has 6 pins (only 4 with a connector soldered) so it's not really the same thing, however the name AT command is "AT+NAMExxxx" which is exactly what happens in my case (where = becomes part of the name). Unfortunately, again the only command that works is ATNAME, none of the other get an answer so I am really at a loss of what to do to change the baud rate of my module.

I think for now I will leave it at 9600 - it works with Amarino and it works with my custom sketches so at least is not totally unusable. I would like to use it with Firmata so I can do some Scratch for Arduino or Snap4Arduino or Johhny-Five without having the Arduino connected to the laptop but maybe I'll just try to buy another BT module one that I may be luckier with and be able to change its speed.

[Update] I tried again: changed the StandardFirmata sketch to 9600, uploaded it to my SparkFun RedBoard (UNO compatible), installed my custom Bluetooth and RGB LED shield, and tried again Arduino Commander and this time it connected and the RGB LED works great, both as digital and analog (PWM) output! I don't know what is different than last time, I am puzzled but happy. My Windows machine was able to connect to the module, hopefully my Linux Mint box and Raspberry Pi will work as well so I can be on to the next step, probably a Johhny-Five little robot.

Arduino sensors to Raspberry Pi using 433 MHz radios

Finally getting to wrap up my first end-to-end project using Arduino and Raspberry Pi talking via inexpensive 433 MHz radios - the distance over which they work is pretty small but this instructables explains how to add an antenna which dramatically improved the distance. The main idea was to have multiple Arduinos with TX radios, each equipped with DHT and PIR sensors; they all send the data to the Raspberry Pi which posts it to the web and also writes it to a local database. In addition to the values from sensors, I am also sending the voltage level, hoping that this way I can monitor the discharge of the batteries (I am not sure if this works or not, I didn't use an analog pin for this, I am simply getting the voltage on the MCU, using code from this great instructables).

The code for both the sender (Arduino) and the receiver (Raspberry Pi) is in my github repo. The comments in the code pretty much explain everything (how it works, how to connect the sensors and radios, and so on). Here are just some quick ideas that may be interesting.

• I wanted to transmit all the data in one go so I combined 4 numbers into one long, as described in both sender and receiver code.
• The transmission between the radios is pretty flaky, that's why I am repeating the send a lot on the Arduino and there is code on the receiver to ignore identical values coming in a 30s interval. This is OK because transmissions from different stations have different station codes so even if the sensor values are the same, the actual overall value is different. Same for a motion sensor: the ON value is different than the OFF value so even if they happen a second apart, both will be received.
• I started by posting the data to SparkFun's data service, then added Dweet.io and in the end settled on ThingSpeak and I'm also saving all the data to a local SQLite database. See some notes about this later in this post.
• The code in github is ready to use: just change the stationCode for each Arduino station and use the right API keys in the Raspberry Pi code.

Notes about posting to the web: there are a lot of great IoT services out there with free tiers, to start with I chose the few mentioned above that have a simple API and that accept GET. Each free service has certain rate limits so I need to consider the data volume I will be posting. With one station only getting the temperature sensor data every 3 minutes, this means 5 posts in 15 min. The motion data is a bit more intensive, roughly 2 posts 5 sec apart (ON and OFF) every time the motion sensor is triggered which at the most (sensor triggered all the time) means 24 posts a minute. Because there is potentially a lot more motion data, I am using 2 different data streams (channels, feeds): one for temperature, humidity and voltage and one for motion; even so with a lot of stations there is the risk of missing data (according to each service rate limits as described below) so I decided to also implement a local SQLite database to store the data and eventually process it later and post it (maybe using node-red).

Rate limits:

1. SparkFun's data service is limited to making 100 log requests every 15 minutes. Given the 5 posts in 15 min, the temperature data stream can accommodate 20 stations without losing data which is more than I need. The motion data though may accommodate only 1 or 2 stations (more if there is not a lot of activity around them) without starting to lose data. I will post all the data I can, the remainder being lost.
2. Dweet.io holds on to the last 500 dweets over a 24 hour period so while there won't be data loss, the motion data will probably cover only a few hours at the most, even for just a couple stations.
3. ThingSpeak has a rate limit of an update per channel every 15 seconds so more than one station per channel will more than likely run into this limit (even 2 temp stations sending data every 15 minutes can happen to send data less than 15 sec apart); I could wait and retry until the post goes through but this would delay the code and risk missing data sent by the stations. Because of this, I decided to tie the local db data to this service: every time I post to ThingSpeak, I check the response: if > 0, the post was successful, I will log the data to the db with a flag of posted=true (1); if = 0, the post was not successful so I will log the data to the db with a flag of posted=false (0). Later I may create a node-red flow to get all the db data with posted=false and repost it to ThingSpeak; each row records the UTC time of the actual insert so I can send it along with the data, the measurements getting recorded at the actual time they took place not the time I post them.

If you find anything useful in this post and the code I am very happy. Most of this stuff is on the web but putting it together in a real project took some work; I am happy I did it and learned so much in the process. When I started I had no idea how to use a radio on either Arduino or Raspberry Pi, how to work with a PIR sensor and how to use interrupts, how to write any real C code, to work with sqlite and post to REST services on Raspberry Pi and much more. I used a lot of info from the web, from too many people and websites to thank individually but a big thank you! goes to everyone that provided help and information in a way or another.

My first useful project ever - a night light

Following a simple idea like the one on Evil Mad Scientist I was able to build my very first useful electronics project - I know it is really nothing but for me it was a breakthrough. For more explanations about how this works, please visit the link above, they do a great job of explaining it all.

I had around a string of LEDs that work when powered by only 3V so I was able to replace the LED in the diagram with a full string of them; packed tight in a glass bowl they actually look pretty good.