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Sensors Archives - Mike Seiler, MSEE
Adventures in Engineering Trade-Offs

Sensors

3 Amazon IoT Button Hacks

The Amazon IoT button is an amazing little device.  It can run for about 1000 button presses from the built in lithium AAA battery.  It’s easy to connect it to the local WiFi network.  But you don’t have to limit yourself to just pressing the button.  I present to you 3 additional uses that require only a modest amount of hacking.

Three Amazon IoT Button Uses

I’ve ordered the project from simplest and fastest all the way up to simple and fast. But if you don’t know which end of the soldering iron gets hot, then stick with the first project.

AWS IOT console

AWS IOT console setup. (The blurred text protects my button)

Door Bell

Stick the Button by your front door (maybe with a label that says “Door Bell”)  I have it set up through IFTTT to send me a text, “Somebody is at the front door.”  Follow the instructions on the Amazon Button page.

Your Amazon Iot Console should look something like the picture on the right.

Let’s Get Hacking

Prelude – How to safely crack open the “no customer serviceable parts inside” case.

  1. Remove cover label.  You can catch a corner by the tiny microphone hole with the sharp tip of a knife.  The label peels off.
  2. Remove three Torx #5 screws.
  3. Crack case. Again using a sharp knife tip, carefully wiggle the blade in at the rounded end next to the big button.  Don’t do this at the other end because there are electronics close to the edge.
Schematic for both the flood alarm and motion sensor.

Schematic for both the flood alarm and motion sensor.

The next two hacks bypass the button.  A simple additional circuit is added.  To prepare solder an access wire to

  1. the battery plus terminal,
  2. the battery minus terminal and
  3. to test point TMF27, which is next to the microswitch that is under the big button.  There is a via over part of the ‘7’ which makes it a bit hard to read the number.

Flood Alarm

Flood Alarm using Amazon IoT Button

Flood Alarm using Amazon IoT Button

Here the Button is in my basement, in the utility room.  A drop of water simulates a button press, which triggers a rule and texts me, “Flood alarm!” The V+ battery voltage causes a small amount of current to flow into the base of the transistor when water is present at the water probe.  R1 is a current limiting resistor which protects the T1 if the probes are shorted together. T1 can be either a 2N2222 or 2N3904 or pretty much any NPN silicon transistor with a gain of around 100.   C1 gives a spike or pulse so that the button is only single pressed.  SV1 is the connector to the Amazon IoT Button.  Pin 1 is the battery +, Pin 2 is the battery -, and Pin 3 goes to test point TMF27,  R2 provides a discharge path for C1.  (R3, SV2 and G1 are are part of the motion detector and not used for the flood alarm.)

 

Motion Sensor

A inexpensive HC-SR501 PIR motion sensor is powered by a lithium battery.  The PIR motion sensor uses very little current and the 18650 battery should last for years before it needs to be recharged. Again, just about any 3.6 volt lithium battery should work.  The 18650 is what I had handly.   The  PIR motion detectors cost only about a dollar on eBay. R3 provides current limiting to the base of T1, which inverts the signal so that it looks like a button press.  The 18650 battery + goes to the pin marked Vcc on the PIR. Likewise, battery – goes to the pin marked GND.  Finally the PIR out pin goes to the base of the transistor through R3.

Oh! and I just noticed an error on the schematic.  The 18650 battery – goes to pin 2 of SV1.  In other words, the ground of the two batteries in the system needs to be connected. The PIR sensor has two setting pots.  Set the X1 to minimum (all the way counterclockwise) and the SX pot to the desired sensitivity.  The output is sent to the Button.  IFTTT texts me, “Movement detected!”  The water probe, R2, C1 and R1 are not used for the motion sensor circuit.

Keep in mind that the Amazon IoT button is only good for about 1000 motion detects.  This is fine if you are only expecting a few motion triggers a day, but the circuit will only last months or weeks if there are frequent triggers.  In case of frequent triggers, you may want to build a power supply. As it says in the text books, “That exercise is left to the reader.”

So, dear reader, does this post give you ideas about what else you can do with an Amazon IoT Button?  Let me know!

Update June 20, 2016

Here are two more uses for the IoT button

  1. A better mouse trap.  Modify a regular spring loaded bar mouse trap with a contact closure. The contact closure, of course is picked up by the IoT button by capacitive coupling.   This signals that a mouse is ready for “disposal” and that the trap needs to be reset.
  2. A tapping sensor switch similar to the Knocki.  I’m speculating that a piezoelectric energy harvester can trigger the IoT button the knock pattern for a single tap. double tap and maybe even long press.  If the piezoelectric sensor does not provide enough energy to trigger the IoT button then we can use a ultra low power op amp to boost the signal.

 

Beyond NEST – Wood Fireplace Insert and Pellet Stove Controller

Previously,  I had experimented with an Arudino Uno based fireplace insert blower controller. That experiment evolved in having two displays – one for the time and temperature, another for a graph showing temperature over time.

But, it makes sense to combine the two displays in the previous design into one display.  A common, inexpensive display available are  240×320 TFT LCD displays based on the ILI9341 chips. The one I got from Banggood (I couldn’t make up a name like that if I tried!) plugs directly on an Arduino Uno.  However, this makes it difficult to find pins for the thermocouple interface.  So, I upgraded to an Arudino Mega, which gives me more memory, and oodles of spare I/O ports.

Wood Fireplace Insert Blower controller with graphic display

Wood Fireplace Insert Blower controller with graphic display – double click to enlarge.

Note in the picture that the display the time is shown on the first line, temperature on the second line, and then time vs temperature graph below that.

Temperature is graphed once a minute, which makes it easy and entertaining to see the temperature hump created by throwing in a log. A grid with blue dots every 10 minutes and white dots every hour further helps give structure to the graph.  Horizontal dots are 50 degrees Fahrenheit intervals.   I personally find this graph quite useful for figuring out when, and how big a log to throw on the fire.   However, I’m sure I’m going to be dinking with the user interface for quite a while to come.

The DS3231 real time clock (RTC ) from the previous design continues to be on the I2C bus, which is also more accessible with the Mega because the I2C pins are brought out in a second location that is not blocked by the LCD shield.

A few months ago, I did a survey of digitally controlled fan controllers. All the designs seemed more complex and expensive than I though necessary.  When I found a AC motor speed controller on eBay for about 2 bucks, I ordered one.  In the mean time, I saw a post about using a LDR (Light Dependent Resistor) to complement the variable resistor (Pot) and thought I’d give that a go.  By the way, I left the pot in the circuit, so I can bypass the Arduino if I want.

I came up with an Arudino interface consists of a green LED shining onto the LDR , both of which cost about a nickle on eBay.  What I don’t understand is why a commercial version (Vactec or Vactrol) of this type of opto-coupler cost $6, when I can build one myself for 2 parts costing a dime, plus a bit of heat shrink tubing.  It did not hurt that I already had these parts in my “junk” box.  The transfer function my home brew unit is also quite linear if graphed on a log/log scale. The opto-coupler is the nearly  vertical black cylinder on the upper left of the picture. However, it’s taking a bit of experimenting to get a good dynamic range and resolution when coupled with the $2 motor speed controller.  Selecting the right series resistance for the LED is the key.  The LDR has a lot of useful smoothing capacitance and can handle a higher voltage than your typical opto-coupler.   The lDR capacitance is useful because the so called Arduino “analog” output is actually pulse width modulation at 750 Hz.

My other reason for creating a second prototype is that I have a pellet stove with a blown controller board in the basement.  What it takes to fix it is a blower speed controller – and I now have two working prototypes.

I did a bit of market research and it appears that the market for pellet stoves and fireplace inserts are on the order of hundreds of thousands of units sold in the USA per year.  Perhaps there is a path to commercializing my design?  I’m going to have to give the design of a demo worthy case some thought.

Wood Stove Fireplace Insert Controller – Beyond NEST

 

Wood Stove Fireplace Insert Fan Speed Controller with Graphic Display

Wood Stove Fireplace Insert Fan Speed Controller with Graphic Display

There are some home temperature control situation that don’t work with a NEST.

In my example, I am controlling the fan speed for the blower of my wood fireplace insert.

I want to be able to control the fan speed depending on stove temperature as well as time of day.  In addition, it’s helpful to have a display that graphs the stove temperature for the last couple of hours.

In the prototype, I am showing the time, and blower exhaust temperature in Celsius and Fahrenheit. This forced air is used to heat over 1000 square feet from my fireplace insert.

Modules visible are the arduino UNO, AC fan speed controller, DS3231 real time clock module, 2×16 LCD display, thermocouple interface and 128×64 OLED graphic display. Usually, the graphic display shows a gradual curve as a piece of wood burns.

My next step is to combine the two displays into one 320×240 display (code already written) and put the historical temperature data in the cloud.