Repurposing an Amazon Dash Button - written by on 2018-01-21

Repurposing an Amazon Dash Button

The most known, cheapest and best IoT button, repurposed.

Amazon's Dash Buttons are quite incredible. For just $5 you can modernize such a common task as shopping. With a single press, you can order from dishwasher to toilet paper, instantly and effortlessly. These buttons connect via WiFi to Amazon servers, and when they're done, they shut themselves off.

Taking advantage of this, we can easily repurpose them for all of our IoT needs, in a cheap way. The process is as follows:

  • When the button is pressed, it connects to the WiFi access point
  • We detect that connection
  • We act accordingly

Simple, isn't it? Let's get it working

First we have to configure the button. For this we'll follow Amazon's instructions, but when prompted to choose a product to order, just quit the app, so no product will be ordered.

We'll also need the button's MAC address. With this code, every device connecting to the network will be displayed. Just run it and click the Dash Button a few times.

from scapy.all import *

def arp_display(packet):
  if packet[ARP].op == 1:
    print('ARP Probe detected: ' + packet[ARP].hwsrc)

sniff(prn = arp_display, filter = 'arp', store = 0, count = 0)
Dash

We've got the MAC address. Great! Now, slightly modifying the code, like this:

from scapy.all import *

def arp_display(packet):
  if packet[ARP].op == 1:
    if packet[ARP].hwsrc == '50:f5:da:df:0b:80': # change this
      print('Button has been pressed!')

sniff(prn = arp_display, filter = 'arp', store = 0, count = 0)

Will make the code only react to the Button's address.

Dash 2

With this, now it's just a matter of tailoring the script to suit your personal needs. From sending an email to controlling another IoT appliance, the possibilities are endless.


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Simplifying the MCP23017 - written by on 2016-03-01

Simplifying the MCP23017

Library for the Raspberry Pi written in Python that simplifies the use of the MCP23017, a 16 bit GPIO expander

The MCP23017 is a very useful IC. It provides 16 GPIOs, and it's ideal for expanding the ports of a Raspberry Pi. It even includes pullup resistors for each pin, and all of this using i2c.

You can find the datasheet for this chip here

But all this benefits come at a price. It is not easy to use, or at least, not easy to use initially. The MCP23017 operates entirely based on registers (Page 9 of the datasheet), and depending on which register you are writing to, you'll be able to change the direction of the pins, state, pullups... Also, GPIOs are divided into two different banks, and they are independent from each other.

To simplify this boring register thing, I created a library, in Python, for the Raspberry Pi. Commands are almost the same as the RPi.GPIO ones.


Here is the pinout the library uses:

Library Pinmap

A very simple code example:

```
import mcp23017_lib as MCP
MCP.start(0x26)
MCP.setup(2, MCP.IN, MCP.PUHIGH)
MCP.setup(1, MCP.OUT)
while 1:
   if(MCP.input(2)):
      MCP.write(1, MCP.HIGH)
   else:
      MCP.write(1, MCP.LOW)
```

This example will set pin #2 as an input, with the pullup resistor enabled and #1 as an output. When the input goes high, pin #1 will also go high.

You can find the library here. It is licensed under the GPLv3.

If you found this library useful, and/or have suggestions, please let me know in a comment :3


Tagged in Software. 2 comments

Upgrading a mouse with a 555 timer - written by on 2015-12-20

Cookie Clicker is fun, but it is necessary to click a lot so my finger gets tired and my mouse broken. So, why not use a 555 timer to automate clicks?

I've been playing Cookie Clicker for the past hour. It is very addicting, but it advances quite slow. It is also necessary to click a lot, so mi finger gets tired and my mouse, destroyed. So, why not use a simple 555 timer to perform automatic clicks? Let's go!

The 555 timer is one of the most sold and used ICs in the world, due to its low cost, ease of use and application diversity, that ranges from a delayed switch to an oscilloscope. Here's a datasheet for the chip.

The timer has several working modes, monostable, bistable and astable. The one we need is the astable one.

In this mode, the chip will provide a constant pulse sequence specified by us. This is what we want to achieve, fast and constant pulses, just as if we were clicking the mouse.

Here's the circuit:

Circuit

Quickly making this circuit on a breadboard, and connecting the output to an LED (instead of the mouse) we get this:

Breadboarded circuit

Breadboarded circuit

What frequency is being achieved with this circuit?

Frequency

Wow! 18.5 Hz! Quite impressive, isn't it? That's a huge improvement over the manual click. Oh, and don't forget the period:

Period

Furthermore, we can calculate charge and discharge times:

Charge

Discharge

After all this calculations, and checking that the circuit is working properly, let's solder everything. In short, you must first check that there is room inside the mouse to house the circuit. It will be powered by the USB bus power itself. The following photos describe this process:

Mouse

This mouse is very easy to open. Just 4 screws on the base and the top just pops off.

Opened mouse

Next, remove the board from the case and analyze where cables should be soldered (V+, V- and signal).

Diagram

V+ and V- come directly from the USB, and the signal wire should be soldered to the push button contact. This way, the button will preserve its original behaviour, but when we press the new added button, the signal will be sent through the original, performing the clicks. After connecting everything, we proceed to the reassembly.

Everything in place

Be careful when accommodating the cables! Oh, and, my finger is pointing to the new button. After everything is again in place, my mouse looks like this:

Finished mouse

And last, but not least, quick check on cookie.riimu.net/speed

Clicks!


Tagged in Hardware. 0 comments