Friday, January 23, 2015

Moteino to Raspberry Pi over Serial v3

I was able to get my Moteino host talking to my Raspberry Pi over the Pi's serial port.  Last time, it was working but the information coming over did not make sense.  The problem was in my sprintf statement in the Arduino sketch.  I had a %d parameter in the command.  Text was getting converted to numbers.  I replaced the %d with a %s and now the sketch sends the correct data to the Pi.

The other problem I was having is that the host was not getting all of the data from the node.  The node was sending three measuring points to the host in with about 100ms between each send.  The host was getting the first and third MPs but not the second.  The easy fix was to put a 500ms pause in between each send.  That gave the host enough time to process each piece of data.  However, that might not be a good solution.  What if two nodes send data to the same host within a half-second of the other?  I need to find a better solution.

After some experimentation, it looks like the problem was the time it took for the Moteino to blink the LED.  After each receipt, I was blinking the LED three times with a 100ms pause between each on-off cycle.  That was apparently too much time.  The middle transmission was getting lost.  I turn the blinking down to one per transmission and the host now receives all transmissions.

Also, the node was sending all three transmissions with three LED blinks with a 100ms pause.  I set the blinks to one per transmission and the host could once again not keep up.

I changed the node to blink once per transmission and pause for 150ms.  This limited transmissions to one every 1/4 of a second.  The host was able to read those.

After all of this, I set the node to only transmit one piece of data every five seconds.  That way the HESA will have time to process each reading.

More time experimenting
The HESA takes 10 seconds to look for water.  Plus, it needs a few seconds to get the temperature and humidity readings from the DHT22.  Finally, it has to update the web page every hour.  That takes a few seconds.

I set my test program on the Pi to sleep for ten seconds if there is nothing in the serial's input buffer.  I also set the node to send some data every few seconds.  When I do that, the host misses 2/3 transmissions each cycle.  That is not good.  Here is the code I am using:
import serial
import time
port = serial.Serial("/dev/ttyAMA0", baudrate=115200, timeout=3.0)
while True:
    rcv = ''
while port.inWaiting() > 0 :
    rcv = port.readline(255).strip();
if (rcv != "") :
    print ("Incoming transmission: " + rcv);
else :
    print ("Sleeping");

 I tried something different.  I set the timeout to 0 and read the port every ten seconds.  Here is the code in this case:
import serialimport time
port = serial.Serial("/dev/ttyAMA0", baudrate=115200, timeout=0.0)
while True:    rcv = ''    rcv =
if len(rcv) > 0 :    print ("Incoming transmission: " = rcv);else :    print ("Sleeping");    time.sleep(10);
Now, the program reads all of the data in the buffer, but it reads it as one big string.  Since I am sending the data in three transmissions with EOL, the data looks like this:

Incoming transmission: 002|101~3369.00

I will change the node program to do one transmission with all data in one long string.  That is for another day.

Friday, January 16, 2015

Connect to Raspberry Pi Over Serial Connection

Tonight at my weekly me time at the Milwaukee Makerspace, I am going to attempt to get my Moteino connected to my Raspberry Pi using the serial connection on the Raspberry Pi.  Also, to be a bit different, I am going to try to take notes on the blog as I go.  This will either help me take better notes or make this blog entry completely unintelligible to any  reader who does not think like me.

There are instructions to work with the Raspberry Pi's serial port at this web page:  I scrolled down to the section titled "Connection to a microcontroller or other peripheral".  There are several things to do to stop the Linux kernel from using the serial port.  This is a prerequisite.  It looks like there is a script someone made to do all of these things automatically.  I am going to try to do the steps myself.

I edited the /boot/cmdline.txt file.  Also, commented out a line in /etc/inittab that opens a login prompt ("getty") on the serial port.

Rebooted.  Logged in with no problems.  There are two checks on the web page that you can run to verify that you did it right.  Both checks passed.  

The next step is to try interacting with the serial port using Python code.  I installed the PySerial package by typing 
sudo apt-get install python-serial 
at the prompt.  While the install was running, I noticed a message saying that there were some packages that were no longer used that could be uninstalled.  I ran 
sudo apt-get autoremove
to get rid of those packages.

This page has a very small python program to test the serial connection.  I used nano to create it. 

The first test I did was to connect the Raspberry Pi's serial pins to the serial pins on the Moteino --
 Tx to Rx, Rx to Tx, and Gnd to Gnd.  Then, I connected the Moteino to my Linux laptop using the FTDI adapter.  I loaded the Arduino IDE on the laptop, uploaded the HESA_Host sketch, plugged in the USB to the Moteino, and ran the python program.  Nothing happened.  I don't know if the problem was that the Moteino does not know what to do when there are two serial connections or if my sketch is bad.

The next test I did was to bypass the Moteino and connect the serial wires from the Raspberry Pi directly to the FTDI adapter.  That test worked.  The terminal screen on the Arduino displayed the output from the Pi and the Pi received the text I typed in on the terminal screen.  Cool!

Tried again with the FTDI connected to the Moteino and the Moteino connected to the Pi.  Made some small modifications to the sketch and tried uploading it to the Moteino.  The sketch would not upload.  

Unplugged the TxRx wires from the Pi.  Now, the sketch will upload.

For the next test, I changed the python code so it will send the letter "t" to the serial port every second, read the results on the serial port, and print the results, if any to the screen.  I also connected a wire from one of the 5v outputs on the Pi to the VIn pin on the Moteino.  I ran the python code and it worked perfectly.  The Moteino faithfully sent its temperature back to the Pi everytime it received a T.

Time to try the whole solution.  I setup my node with the DHT11 temperature sensor.  Then, I started the python program and waited a few seconds.  Next, I powered up the Moteino host.  It transmitted its messages from the setup part of the sketch.  Finally, I powered up the Moteino node.  It started transmitting its data every few seconds.  Everything worked.  The host received the transmissions and sent them to the Raspberry Pi.  The python program displayed the transmissions on the screen.

One problem is that it looks like the python program started displaying the ascii text as hex characters, ex. 0\xe0\x00.  That seems to have started after it received a "]" character.

Tried changing the baudrate on both devices to 9600.  That did not help.
Tried adding a \n to the end of each transmission to the serial port.  That did not help.
Tried putting a 1ms delay after every transmission.  That did not help.

The weird thing is that if I send a T to the Moteino, the sketch returns the temperature text with no problems.  Anything else looks like hex.

Figured it out.  I had some code in the sketch turn off the Moteino in between transmissions to save power.  This was the cause of the garbled code.  Turning off the power save feature fixed the problem.  I don't really need the power save feature since the host Moteino will get power from the Pi.

The new problem is that the data being sent to the PI does not appear to be the data the node is sending.  The data should be something like "002|102~87", but it is some other combination of number.  I'll have to look into that later.  

Also, need to figure out how to know when a batch of data is from one node.  Maybe I could put some text around each end of the package.  For example, ">>>002|102~67<<<".

I'll have to figure that out some other time.  That's enough for one night.

Saturday, January 3, 2015

Moteino Node Talking to Host

After about two weeks off for the holidays, I spent time at the Milwaukee Makerspace working on the Moteinos for my Home Environmental Sensor Array.

3D Print of a Battery Holder
As part of the node solution for the HESA, I want to have a complete stand-alone package that includes a holder for the battery.  Also, I want to have 6v battery for the power supply since the Moteino needs at least a 3.2v input.

I have a 6v Lithium battery from Energizer.  I made a case for it but it is not ideal and not reproducible.  I found a Thing on Thingiverse to 3D print a holder for a Panasonic Lithium battery.

I printed the holder on the Cube Pro Trio 3D printer at the Makerspace.  The printer is very easy to use.  I was hoping it would be more reliable than the other printers we have but my first print failed.  I printed the holder in draft mode and it finished but the corners pealed up a bit.  Also, I found out that the Panasonic battery is longer than the Energizer and the terminals are in different spots.  So, I won't be able to use the holder and will have to find a different solution.

On the plus side, I learned how to use the CubePro Trio printer.  This is a professional-grade 3D printer that should make high quality prints.

ACK Testing
The last time I played around with the Moteino, the node was sending data to the host but the node was never getting an ACK back from the host.  I tested combinations of all three Moteinos with the same results.  I posted something on the Moteino forum and the response was that it should work. I finally got back to testing the ACK feature and was able to get it working -- sort-of.

I think the original problem is that I did not have the antennas attached to the Moteinos.  I soldered antennas onto all three Moteinos, and they now send and receive ACKs properly.

However, this gets more and more unreliable as the distance between the node and host increases.  When the distance is less than 20 feet, the ACKs are almost always received.  At 50 feet, ACKs are received about 50% of the time.  If I go over 100 yards away, almost no ACKs are received.

I posted a message on the Moteino forum to see what the problem is.  However, I also decided that I don't care about ACKs for the HESA.  For now, I can continue without this feature.

Finally, I created a sketch for a node on the HESA network.  The sketch will read and transmit the following information to the host:
  • Notification that it is on-line on bootup
  • Battery voltage
  • Temperature from the RF69 chip or from a DHT sensor if installed.
  • Humidity from DHT sensor if installed
The code is flexible enough to request ACKs or not when sending data.  The device will also sleep between sends.  This should make the battery last longer.

The next step is to connect the host to a Raspberry Pi and have the Pi read the serial inputs.  Then, I need design a circuit board and complete solution for the node.  Finally, I need to make the HESA python program on the RPi send node data to the SQL database.

Saturday, December 20, 2014

Power Monitoring with the Moteino -- Attempt #2

This weekend at the Milwaukee Makerspace, I continued trying to get my Moteinos to communicate to each other.  I want to get a node to send its power level to the host.  I performed a number of tests and eventually accomplished the goal.

Basic TxRx Test
First, I numbered the Moteinos 1, 2, and 3.  Each Moteino was setup at a frequency of 915mhz.  The high power setting for the RFM69HW was set on all Moteinos.  For the first test, I opened the serial terminal window in the Arduino IDE on each Moteino so I could see the messages it was sending.  For the other tests, the terminal was only on the Receiver.

The test involved uploading the TxRxBlinky sketch on each Moteino -- one as the Receiver, and one as the Sender.  I hooked a button up to the Sender.  Once both Moteinos were powered up, I pushed the button on the Sender.  This caused the LED on the Receiver to change state -- on to off or off to on.  The Receiver also sends some text to the serial monitor.


All tests passed.  All Moteinos can both send and receive.  Also, they all operate with either the USB as a power source or the Lithium 6v battery as the power source.

Gateway / Node Test
For the next test, I used the Gateway / Node sketches from LowPowerLab.  The Gateway sketch was loaded on the Receiver Moteino and the Node sketch was loaded on the Sender Moteino.  All Moteinos were set at 915mhz frequency.  The high power setting was set on all Moteinos.

Before testing a pair of Moteinos, I loaded the Node sketch on one Moteino and watched what happened with the serial monitor.  The Moteino outputted exactly what it was supposed to.

Next, I uploaded the Gateway sketch to a Moteino and started testing.


All tests passed.

Custom Node Test
Now that I know all of Moteinos can talk to each other, I tested a custom node program.  It is set to transmit at 915mhz.  The high power setting for the RFM69HW is set.

The custom program is a modified version of the Node sketch from LowPowerLab.  The sketch reads the voltage from the Moteino and transmits it to the host.  (More information about the code to read the voltage is in this post.)

I had the same problem with the sketch that I had last week.  If the Node program tries to read the voltage using the readVCC function, then tries to use the radio.sendWithRetry function, the Moteino appears to reboot--it is re-running the setup function.  If I comment out the line that calls readVCC, the rest of the code processes normally.  However, the send line prints the message indicating it failed.  

After a lot of testing, I realized that the failure message I am getting is always there -- even with the code that comes with the Moteino.  I ran my Node program and the Host displayed the voltage from the Node.  The code works even though the failure message prints.  I don't know if there is something wrong with the code or if I don't understand how the read.send function is supposed to work.

I don't know why the Moteino was rebooting.  I did fix that problem by starting over with the original Node program and adding my code bit by bit.  The problem did not re-occur.  Maybe I had some invisible characters in the code.

Finally, I tested the voltage that is read by the node.  I connected a variable power supply to the power input on the Node.  This let me vary the input voltage.  I started at 6 volts and slowly turned the voltage down.  Sending any voltage over 3.2 registers as 3349 millivolts.  Once the voltage was turned down to 3.2 volts, the device read 3205 or 3196 millivolts.  When the input got down to 3.1 volts, the node stopped transmitting.  So, I will be able to use this code to monitor my battery's voltage.

One of the next steps is to understand how the node and host communicate.

  • Can the node sleep until the host calls it?  
  • If the node sends data to the host, will it get lost?  Is there a way to know for sure?
  • How do we make the device truly low-power?
  • What does the Ack do?
Another step is to connect the host to a Raspberry Pi and have the Pi read the serial inputs.

RPI serial console:


Sunday, December 14, 2014

Possible Smoked Moteino

As I mentioned in my last post, I inadvertently plugged power into the GND pin on one of my brand new Moteinos.  There was a small puff of smoke and I quickly unplugged the power.  However, I had a bad feeling that I just ruined my $20 device.

I tested the Moteino to see if anything still worked.  First, I plugged in the FTDI adapter and used a USB cable to connect the Moteino to my PC.  The Arduino IDE software saw the board.  I uploaded the "Fade" example sketch to the Moteino.  It worked.

Next, I loaded the TxRxBlinky example sketch for the Moteino.  I was able to use the Moteino as a Sender device.  I assume that means that the transceiver is also working.

Finally, I used a multimeter to check the voltages.  The Lithium battery I had hooked up was sending 6.27 volts to the Moteino VIN pin.  The 3.3 pin on the Moteino was putting out 3.31 volts.  This means that the regulator in the Moteino is also working.

I think everything is working.  I'm going to try using this Moteino as the main receiver on my Home Environmental Sensor Array.

#Moteino, #Microcontroller, #Arduino

Saturday, December 13, 2014

Testing Moteinos

This blog post is covering my last two weeks of activity on the Moteinos for my Home Environmental Sensor Array.  Topics include

  1. Power supply experiments
  2. Attaching a power supply to a Moteino node
  3. Testing multiple Moteinos

Power Supply Experiments
I spent a good deal of time trying different ways to power the Moteino.  I was hoping that I could use a 3v Lithium battery as a power source.  That way, I could have an easily replaceable and cheap power source.  However, the coin cell battery I used did not appear to provide enough power to run the Moteino.

Next, I tried a 3.6v Lithium battery that I found in the battery box at the Makerspace.  It put out about 3.6 volts on its own.  After connecting it to the Moteino, I used a multimeter to see how many volts were going into the Moteino.  It registered at about 1.4 volts.  Not sure what is happening but this battery does not provide enough power for the Moteino either.

Finally, I tried using a 6v lantern battery as a power input.  That worked better.  When I tested the voltage with a multimeter, it registered 6.23 volts.  After I connected the battery to the Moteino, I tested the voltage by putting the test leads on the GND and VIN pins on the Moteino.  It registered 6.17 volts.  Since the Moteino has a built-in power regulator that limits the voltage to 3.3 volts, this is more than enough power.

In order to power nodes, the Moteino needs a power source that delivers between 5-9 volts.  The two options are a 6v Lithium battery or a 9v NiCd battery.  I would prefer the smaller battery because it will waste less energy when the Moteino converts the voltage to 3.3 volts.

Attaching a Power Supply to a Moteino Node
Now that I know how much power I need to supply, the next task is to figure out how to attach power to a Moteino that will operate as a stand-alone node.

I bought a 6v Lithium battery as an external power source.  It is just a bit bigger than a 9v battery.  Also, the power ports are recessed.  This makes it difficult to attach wiring to the battery.

My first idea for a reliable power storage solution for the 6v battery was to re-use an existing 9v battery container.  I found an old clock radio on the hack rack at the Milwaukee Makerspace.  The radio had a space for a 9v battery built-in to one part of the plastic case.  I cut out the 9v battery compartment from the case.

I settled on the idea of using screw heads to connect to the recessed battery terminals.  First, I cut a small piece of balsa wood to fit into the bottom of the compartment.  The wood is just a bit smaller than the compartment.  The wood is just big enough to not move around.  Also, when the battery is inserted into the compartment, it will keep the wood from moving.

Next, I put two screws through the wood and cut off the extra length of each screw with the metal bandsaw.  Finally, I attached wires to each screw.  In hindsight, I should have put the aluminum strips on the top of the wood.  That would have helped the conductivity of the wires to the screws.

Putting the battery into the compartment so it has good contact with the screws is a bit tricky since I can't really see what is going on.  However, once the battery is in properly, it delivers 6v.  I can connect the wire leads either to a prototype board or to input pins on a circuit board.  Although this does work, it is not an ideal solution.  Ideally, I would like a solution that works as easily as traditional battery connectors.  Either I could rig up a cap like 9v batteries have or I need a more cozy container that is a better fit for the lithium battery and makes a good connection every time a battery is inserted.  Maybe I could 3D print a container.

Also, I was testing the battery with one of my Moteinos and I inadvertently attached the positive wire to the GND pin on the Moteino.  The Moteino started smoking.  I immediately pulled out the wire but I don't know what damage was done.  When I connect the Moteino to my computer with the FTDI cable, it powers up.  The Arduino IDE client sees the device.  I uploaded a sketch to the Moteino that made an LED blink.  I still need to test the RF device.  If that works, the Moteino may not have been damaged at all.  That would be a blessing.

Testing Multiple Moteinos
I purchased two more Moteinos -- one for my first node, and one for backup or the second node.  The

Moteino site has a section on programming the Moteino.  One of the Arduino sketches allows you to test a receiver / sender pair of Moteinos.  When you press a button connected to the sender Moteino, it sends a signal to the receiver that toggles an LED -- if it is off, it turns on, and vice-versa.

I was able to successfully test this with two of the Moteinos.  Now, I know a bit more about using the Moteinos.  Next, I need to figure out how to connect the receiver Moteino to my Raspberry Pi.  Another next step is to write a sketch to read something on the node and send it to the receiver Moteino.

Friday, November 28, 2014

Power monitoring with the Moteino -- Attempt #1

This week, in my regular time at the Makerspace, I experimented with the Moteino I recently purchased.  I want to use the Moteino as a temperature sensor in my Home Environmental Sensor Array (HESA).  One thing I would like the sensor to do is measure the voltage coming from the battery and report it back to the host.  This way, I will know when a battery on one of the sensors is about to die.

The Moteino is fully compatible with an Arduino UNO.  Vishal from the 'space told me that the Arduino has the ability to determine the incoming power.  There is an internal reference voltage that always measures 1.1v.  This reference voltage can be used to more accurately measure the input voltage to the Arduino.  Here is a web page that talks about this in more detail.  That web page also has code to measure the input voltage.  Below is the code that I used to measure the voltage on my Moteino.  The output consistently read 3369 millivolts.
long readVCC() {  // Read 1.1V reference against AVcc  // set the reference to Vcc and the measurement to the internal 1.1V reference  #if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)    ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);  #elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)    ADMUX = _BV(MUX5) | _BV(MUX0);  #elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)    ADMUX = _BV(MUX3) | _BV(MUX2);  #else    ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);  #endif     delay(2); // Wait for Vref to settle  ADCSRA |= _BV(ADSC); // Start conversion  while (bit_is_set(ADCSRA,ADSC)); // measuring   uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH    uint8_t high = ADCH; // unlocks both   long result = (high<<8) | low;   result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000  return result; // Vcc in millivolts}
void setup() {  // initialize serial communication at 9600 bits per second:  Serial.begin(9600);}
void loop() {  float voltage = readVCC();  // print out the value you read:  Serial.println(voltage);  }
BTW, after uploading the program to the Arduino, I opened the serial monitor by clicking on Tools, Serial Monitor.  The serial monitor displays the output from the Arduino.

Next, I wanted to see what the voltage would be from an external power source, as opposed to the Moteino getting power over the USB cable.  I connected 3.5v power from an adjustable power supply to the VIN pin on the Moteino.  The voltage displayed by the program never changes from 3369 millivolts.  I am not sure if that is because the Moteino was still taking power from the USB or if the built-in power regulator works with any power input.  

I plugged my Arduino Uno into the USB port on the computer and uploaded the script.  It consistently reported 5068 millivolts.  Adding 3.5v power from the external power supply on VIN did not change the readings.

I need to figure out how to get the Arduino or Moteino to send data back to my computer or maybe to a Raspberry Pi without using a USB cable.