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5 Posts authored by: Cabe Atwell

Disclaimer: I’m an engineer, not a pro film maker. Be advised.

Disclaimer: I’m an engineer, not a pro film maker. Be advised.

 

 

 

 

 

motion detection system 1.jpg

The wireless motion detector project. Three drop-modules report to the monitor in the foreground.

 

 

Motion detectors are cool but running wires out to them is a drag. We wanted to secure an area quickly and conveniently and without sirens or bells letting intruders know that we know that they are trespassing. That means no wires.

And so, it was decided, a wireless motion detecting system would be built.

 

We could picture it in our minds, a portable, self-contained system that would let us know when our parents got home or when Derek was breaching the perimeter around our couch-cushion fort. Derek doesn’t respect perimeters.

 

Design considerations – selecting components

We started with Arduino Micros and went from there. We chose these because they are small and have an on-board USB controller. This allows them to be programmed simply by plugging them into a USB port, just like the UNO. No FTDI adaptors would be needed like as is necessary for compact boards like the Arduino NANO. The version of the Micro used came without pin headers soldered on. This for ease of assembly and to conserve space. The pins would have been harder to solder to and would have taken up a lot more room.

 

nRF24 1.jpg  

For the wireless bit, we selected the nRF24L01+ radios. Note the + at the end of the name. The “plus” models that have a male SMA connector for an external antenna and they have an alleged open-air range of 1000 meters when operated at maximum power.

 

nRF24 adapter 1.jpg

nRF24 radios are extremely finicky when it comes to their power. They do not tolerate supply noise at all. To put the stop to any issues of this sort before they start, we used an adapter board like this. They come with an AMS1117 linear regulator to keep the voltage to the radio at a steady 3.3 volts. They also have a few noise filtering capacitors to keep the power clean.

 

OLED screen 1.jpg 

An 128x64 i2c OLED screen was used to display the status of the sensors. An i2c connection was chosen on purpose. The nRF24 radio communicates via SPI. So, to prevent any conflicts that might arise from having the screen and radio on the same data bus, it was decided use i2c for the screen. Yes, theoretically there should be no problem with putting the two devices on the same data bus. But all too often, reality swings in to ruin your day and you are left screaming about how everything worked fine on paper. To minimize any handholds for Murphy’s and Sod’s Law, communications to the screen and the radio were kept completely separate.

 

PIR sensor 1.jpg

This is the PIR motion sensor used for the drop-modules. The potentiometers on the side control how sensitive the device is and how long the output stays high after motion is detected.

 

battery 1.jpg 

Lithium-polymer battery in the shape of 9-volt batteries was chosen as a power source for the drop-modules and the monitor. Originally, the intention was to use disposable alkaline or lithium 9-volt batteries. However, these types of batteries will not meet the power demands of the nRF24 radios. This point demands a bit of explanation. nRF24 radios draw very little “on” but quiescent. During the short period that they are transmitting their power requirement spikes abruptly. A typical 9-volt battery cannot provide the energy fast enough for the nRF24. This problem can sometimes be mitigated by installing a fairly large capacitor (100uF) in parallel with the battery. Another solution is to do what we did, use a lithium-polymer battery. The particular batteries we chose are very convenient for projects because they combine a lithium-polymer battery with a battery management circuit, a battery protection circuit, and a boost converter. They also have a micro USB port for charging. It’s like five components packed into the shape of a 9-volt battery. Note the tiny hole in the bottom of the battery. This is for a red LED that lights up when charging. The LED shuts-off when the battery is fully charged.

 

Monitor BOM

 

Drop-module BOM

 

 

The Code (Attached to this article)

Code was written up for the drop modules and the monitor. The code for each of the drop modules is identical. During the drop-module’s setup routine, the address selection pins are polled to see what the modules address is. Two modules cannot have the same address. If they did, the monitor will interpret all the received data as coming from the same drop-module, and the system will not work as intended.

 

An ad-hoc protocol was developed for communicating drop-module status back to the monitor. The drop-modules encapsulate all of their data into an unsigned long variable. Each byte of this variable would represent a specific alarm code or the status of the battery. Then, the entire unsigned long variable is sent to the monitor.

 

At the monitor, this variable is broken back down into bytes, and the data is used to determine what drop-modules are active, what its status is and if the signal from any module is dropped.

 

The code for the drop-modules and the monitor share a number of details. They both us the RF24.h library to handle interactions with the radios. Also, they both use the TimerOne.h library. Timer one is used to make sure events like transmitting status and updating the OLED display happen at regular intervals.

 

The monitor uses the U8g2 library to control the OLED.  This library is very easy to use, and it is loaded with easy to use functions for drawing lines and shapes and placing text on the screen. There is a huge selection of fonts to choose from too.

 

At a glance, the code, especially the monitor code looks complicated but don’t let it scare you. It is lengthy, but you have a couple things going for you. It is commented extensively, and it is written out in a longhand of sorts. This makes the code take up a lot more space than it needs to, but it is also easier to understand for the less experienced coder. Oh, and the bulk of the monitor code is subroutines used to refresh the OLED display.

 

 

The mechanical design (Files needed for 3D printing, attached to this article)

All the parts that we knew were going into the project were mocked-up in SolidWorks. The Arduino Micro, the nRF24, the 9-volt battery, the OLED screen. These mock-ups are mostly rough geometric approximations of the real parts. We don’t need a high level of detail to effectively design enclosures for the project.

 

SW monitor 1.png  

From here the enclosure for the monitor was drawn up. The enclosure takes style cues from sources like the Aliens movies and the short videos of Neill Blomkamp.

 

SW drop module 1.png 

Then the drop-module was drawn up. It is designed around a clear plastic toothpick container. The container is clear and just the right size to house all the parts.

 

Putting it all together

The monitor enclosure and the parts for the drop-modules were 3D printed in a pleasing dark blue color. There was nothing very complicated about the build. The components were wired together with short leads, soldered and then covered with heat-shrink tubing. The notable points of the build are illustrated in the pictures below.

 

 

The monitor

schematic - monitor .JPG

The monitor wiring diagram. Start here.

 

 

 

 

{gallery:autoplay=false} Monitor Assembly

monitor module 5 - nRF24 radio.pngHere is the radio installed in the monitor. Notice the two spacers around the SMA connector.

These keep the radio square to the interior surface when the antenna is threaded on - they were made by trimming an old credit card into washer shape with a hobby knife.

monitor module 2 - nRF24 adapter.pngThe pins and headers were de-soldered from the adapter board; this was done to conserve space.

Then, wires were soldered to the adapter and then the whole board was covered with a big piece of heat-shrink tubing.

monitor module 3 - power button.png

The on-off switch slides into the pocket designed to hold it.

monitor module 4 - resistor bridge 1.pngThe voltage divider network for monitoring the battery status was constructed with a pair of 10k resistors.

The entire assembly was covered in heat-shrink - the yellow wire runs to and ADC input on the Arduino MICRO.

monitor module 6.JPG

The reset buttons are pressed into their slots. Friction keeps them in place.

screen & bezel 2.jpg

The conserve space, the OLED screen sits in a 3D printed bezel.

screen & bezel 3.jpg

The screen drops right into the rear of the bezel.

screen & bezel 1.JPG

The screen installed on the outside of the monitor enclosure.

monitor module 8.jpg

Fold everything into the enclosure - be careful not to break anything.

monitor module 7.jpg

Once everything is tucked inside the monitor, fasten the rear covers down with #2 machine screws.

monitor module 1.jpg

Completed monitor - human hand for scale.

 

 

 

 

Building the drop-modules

 

schematic - drop module.JPG

The schematic for the drop modules. Notice the address selection pins 8, 9, and 10. To set the address of the module, a single pin must be connected to ground. Modules cannot share addresses.

 

 

{gallery} Building the drop module

drop module 1.png

The drop modules are assembled with the same methods as the monitor - you can see here that all the components are wired up and protected with heat-shrink tubing.

drop module 2.png

You can see here where the headers and pins have been de-soldered from the adapter board and the nRF24 and wire leads have been soldered in their place - the assembly is covered in heat-shrink after soldering.

drop module 3.png

The PIR sensor is hot-glued into its 3D printed shell.

drop module 4.png

To finish, carefully fold the everything into the containers and seat the tops. Then Slide the retaining ring over the bottom of the containers. Finally, fasten everything together with the long #6-32 screws and nuts. It is a good idea to label the drop-modules too.

 

 

 

How to use it all

 

 

 

 

Conclusion

 

There were a lot of different ways we could have come at this project. We could have used a mesh network that would have allowed for dozens or over a hundred drop-modules, but instead, we went with three. Also, the code could have been written far more efficiently. Especially the monitor code. For anyone who attempts this project we strongly suggest having a go at optimizing the code.

 

We used 3D printed parts and toothpick containers to house our project, but you don’t have to do any of that. Use breadboards and cardboard. Or use plastic food containers. It doesn’t matter. The code and the hardware are oblivious to how good (or bad) they look. Also, for your version of this project, you can use different sensors. You don’t have to use PIR motion detectors. You could use the drop-modules to keep an eye on anything. Use photoresistors to see if someone turns on a light. Replace the PIR sensor with a momentary pushbutton or a pressure sensitive doormat to make a wireless doorbell. Maybe you could use a drop-module with just a tilt sensor to let you know if someone is messing with your bike. Whatever you ultimately decide to do, this project gives you a solid basis to work from.

 

But for now, Derek won’t know what hit him.

 

 

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Have a story tip? Message me at: cabe(at)element14(dot)com

http://twitter.com/Cabe_Atwell

Project build Index:

Arduino Project : Three-Finger Ring - Part 1 Getting started and 3D Printing

Arduino Project : Three-Finger Ring - Part 2 Code & the Circuit

Arduino Project : Three-Finger Ring - Part 3 Assemble the Ring!

 

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Step 6: Assemble the ring and install the components.

At this point, disassemble the breadboarded circuit and begin installing it into the ring. Glue and a hobby knife are essentials in this step. Unless you got lucky or have a printer that fabricates with a nigh-zero deviation from mathematical perfection, you will need to use a hobby knife to trim the printed parts.

 

The power pack is made by sandwiching the batteries together with a positive and negative wire and wrapping the whole affair tightly with electrical tape (Figure 5).

 

Hot glue was used to fasten the parts in place (Figure 6).

 

The #4 screws are used as pins for the hinge and to fasten the ring’s lid down (Figure 7).

 

battery pack.jpg  

Figure 5: The ring battery pack. It is a bit inelegant, but it works.

 

assembling 1.JPG

Figure 6: Glue the parts into the ring.

 

screw it together 1.jpg 

Figure 7: The #4 screws fasten the ring together.

 

 

 

 

Step 7: Power it up and show it off.

You might want to create some fresh images for your ring. Our pics didn’t increase our popularity quite as much as was hoped. Here are a few examples.

 

 

element 14 (12).JPG

danger (9).JPG

eulers relation (3).JPG

konami code (12).JPG

i 8 sum pi (8).JPG

max power (4).JPG

nerd life (8).JPG

ohms law (5).JPG

QT pi (6).JPG

stud muffin (28).JPG

final form (9).JPG

 

 

 

 

Final Notes:

We used a 128x64 OLED screen with that goofy yellow and blue background color. You can use whatever screen you want (almost whatever screen) as long as you adhere to a few guidelines. Make sure that the screen communicates via I2C.

 

The circuit and code do not use the RESET line. If the screen you get does have a RESET line, pull it HIGH by wiring it to the 5V output on the Trinket Pro.

 

If the resolution of the screen is anything other than 128x64 pixels, you will have to:

  • Size your images appropriately using a picture editor. You will not be able to use the CPP arrays in the provided code. You will have to create new arrays for your screens exact resolution.
  • You will have to adjust the U8GLIB_SH1106_128X64 u8g(U8G_I2C_OPT_NO_ACK) line in the code so that the U8glib library knows what screen size to work with. There are no provisions in the code or the hardware for detecting any information on the screen, so you have to tell it what is going on.

 

You are not obligated to use two CR2032 batteries to power your ring. Use a Li-Po battery back, an AAA with a boost converter, whatever. It doesn’t matter. The Trinket Pro can be powered by anything from 5.5-16 volts. If you wanted, there is no reason why a tiny Lithium-polymer battery and a battery management board couldn’t be used in place of the coin cells. Or a solar cell in conjunction with a super-cap or rechargeable battery.

 

Thanks for reading! Good luck with you own ring project!

Project build Index:

Arduino Project : Three-Finger Ring - Part 1 Getting started and 3D Printing

Arduino Project : Three-Finger Ring - Part 2 Code & the Circuit

Arduino Project : Three-Finger Ring - Part 3 Assemble the Ring!

 

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You have everything ready from Part 1 right? Good. Now it's time to program and get images on that screen.

 

Step 4: Breadboard the circuit.

 

Before installing anything, test it on a breadboard. That way, it will be so much easier to troubleshoot. See the electrical schematic in Figure 4.

 

breadboarded.jpg

Figure 3: Breadboard the circuit before installing it.

 

schematic.JPG

Figure 4: The electrical schematic for the Screen Ring.

 

 

Step 5: Upload the code to the Trinket.

 

There are a few special considerations for using the Adafruit Trinket. The IDE available from the Arduino site does not natively support it. You will need to either download a special version of the IDE from Adafruit with the board data pre-loaded, or you will have to follow the instructions on the Adafruit website detailing how to load the board data into the IDE. Either way, you will need to start HERE at the Adafruit introduction to the Trinket.

 

The cornerstone of the Screen Ring code is the U8glib library. It takes care of all the heavy lifting regarding control of the screen. The specifics of this library are well beyond the scope of this article but, if you want to learn more about it, start HERE.

 

 

Step 5-2: Create some sweet bitmaps for the ring.

The Arduino code cannot read PNGs or JPGs and the like. It requires BMP images to be converted into data arrays which are then pasted into the code. One of the easiest ways to accomplish this is to use the online image2cpp converter. Just upload a BMP, convert it and then copy the generated code into the Arduino sketch (Figure 5).

 

There are some rules for getting the converted images to display properly. This can all be done in Windows Paint.

  • Images must be in black and white.
  • Images must be created with a size of 128x64 pixels.

 

start of Array.JPG

Figure 5: The beginning of an array pasted into the sketch.

 

 

Resources: The CODE.

 

Attached to this post is code used in the Three Finger Ring.

 

In it, you can change the code to for any images you convert.

Project build Index:

Arduino Project : Three-Finger Ring - Part 1 Getting started and 3D Printing

Arduino Project : Three-Finger Ring - Part 2 Code & the Circuit

Arduino Project : Three-Finger Ring - Part 3 Assemble the Ring!

 

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CROP+DSC05498.jpg

 

I already teased this project back on "Geek Day," June 9th 2017. It's now completely finished!

 

This writeup will go over all the steps taken to build the screen ring. However, you dear reader won’t have to personally execute every step. You have the option of skipping steps because we will provide the 3D models for the ring and the accompanying code. You can procure the parts and print the ring without any of the design work. The one aspect of the design that you may have to change is the size of the holes in the ring to accommodate finger size.

 

In this section, we are going over all the mechanical aspects of the ring. What parts to gather. And how to get the ring 3D-Printed. (Part 2 is where we will cover the circuit design and code.)

 

Step 1: Decide on the parts to use.

 

For the dangerous end of the ring, we used a 128 x 64 pixel 0.96-inch OLED screen, very similar to this screen here. The exact screen we used is permanently blue with a yellow band across the top third. The yellow top third was probably originally intended to display data like the time and the battery charge.

An Adafruit Trinket Pro 5V provided the brains. It has far more IO than is needed but that’s OK. All those extra pins and features can be used on the next version of the Screen Ring.

 

While the options for powering the ring are many, we went with a couple of CR2032 coin cells. Each coin cell outputs 3V so stacking two of them in series yields a handy 6 volts. This is just enough to power the Trinket and for the Trinket’s onboard MIC5225 to regulate the voltage down to 5V for the OLED screen.

 

Bill of Materials

Quantity 1 - OLED Display, 128x64, I2C

Quantity 1 - Tactile Switch or something roughly equivalent

Quantity 2 - Adafruit Trinket Pro 5V

Quantity 2 - CR2032 coin cells

Quantity 3 - 10k resistor

Quantity 4 – #4 x 0.5” (12.7mm) machine screws

 

Step 2: Design the ring.

 

The ring was designed in SolidWorks, but any 3D CAD software like LIBRECAD or FREECAD will work. Again, you don’t have to design anything if you don’t want to. However, for the those who would attempt it, here is a bit of design advice.

  • It always helps to have at least a nebulous concept in mind.
  • Start by creating 3D models of the parts you know will be used. In this case, the screen, the batteries, the button and the Trinket. The level of detail applied to each of these models is up to you. You may not need to model the Trinket down to the point where all of the components on the board are represented. However, it would be a good idea to at least make the model large enough to fill the immediate space around the Trinket.
  • Start with a box big enough to hold all of these.
  • Position your parts inside the box where you think you would like them.
  • Start removing material where you don’t need it and adding it where necessary. For example, you might add bosses or studs for holding parts.

 

Once this "box full of parts" was designed, it was obvious that a single finger wasn’t going to be enough support it. For stability and coolness, it was decided that three rings bridged together would do the job. To get the size just right, a few of the ring-only sections were printed up and tested on actual hands.

 

3D modeling in progress.jpg

Figure 1: 3D modeling in progress. (NOTE: This image is far from the final design)

 

 

Step 3: Print the ring.

 

The 3D models can be sent off to a service like Shapeways or you can print them up yourself if you have access to a printer. For the ring seen here, we used our MakerGear M2. A quick shout out to MakerGear, the M2 deserves all the approbation it gets. It really is a workhorse.

 

We used this particular blue color (Figure 2) because it’s cool and kind of makes things look like they’re from the future. Oh, and because we had several rolls of that color already on hand.

 

the printed bits.jpg

Figure 2: This blue color is so rad.

 

 

Resources: 3D Models.

 

Attached to this post is a collection of the 3D models used in the Three Finger Ring.

 

You could use this as a starting point for your custom design too.

arduboy.jpg

A new Arduino Gameboy called Arduboy. Nostalgia is fun, and nostalgic games are even more fun. Arduboy is a new and cheap ‘gameboy’ that allows you to play games old-school. (via Arduboy)


I can't believe I missed out on this cute little gameboy-ish system powered by Arduino, with a heaping dose of nostalgia along with it. The creator, Kevin Bates, is calling it an Arduboy and he quit his full time job over a year ago to develop this creation. He even moved to China to get the production line all set up and have his product in the making. Now, that is definitely commitment.

 

The Arduboy is the size of a credit card and has an 8 hour battery life, meaning that waiting for your friend to get out of the bathroom at Starbucks just got way more fun. The Arduboy is powered by Arduino, a black and white 1.3 inch OLED screen, and two piezo speakers. Basically, it has everything you need to game in vintage style.

 

It also had... a great price point, at $29. You can get one for $39 direct from them. The Kickstarter campaign ended with over $433,000 in funding. This is over 17x their original pledge goal.

 

arduboy games.JPG

Arduboy games from the community.

 

The Arduboy is also open source so you can code it to do whatever you’d like. Bates has also sent over 100 developer copies to ensure that there are at least 100 free and open source games available for the Arduboy by the time it gets to you. Some of the games include knock-offs of popular games like Oregon Trail, Flappy Bird, and Ardumon.

 

Bates told the peeps at Engadget that he eventually wants to sell the Arduboy for $10 and have it available for companies to brand and giveaway as conference swag. If that ever happens, I will attend way more conferences. 


If anything, I take away a little inspiration from the Arduboy. The creator took a simple design all the way, committed to the project, and won out in the end. It's time for everyone to do the same...


C

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