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LoFi

LoFi is a very low cost ($5), small, auto-transmitting module. Preassembled and preprogrammed. Simply attach to your appliances or projects!

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This project was created on 06/20/2014 and last updated 18 days ago.

Description
Like many hackers and hobbyists, we dream of a smart home. Although there are third-party transceiver modules and data loggers on the market, they are too expensive and complicated to deploy in volume.

LoFi is a very low cost ($5), small, auto-transmitting module. All you need to do is to attach the modules to interesting appliance circuit points or sensors throughout your home and garden. The data arrives on your PC or can be sent to the Internet with a WiFi hotspot.

No programming, no protocols to learn, and no carrier boards for you to make. Just attach!

Using your desktop or laptop, you can set trigger levels on individual modules to tell them when to transmit. For example, send an update when the voltage changes by more than 1 V on the vibration sensor near the garage door opener. You can also set the module on a timer, such as hourly on your garden monitor.

The possibilities are endless!
Details

SENDER

The sender is compact (1.25 sq. inch) and operates from 1.8 to 5.5 V. The module consists primarily of an Atmel ATtiny84A which monitors the inputs and outputs the data. A red and green LED provides visual status.

The sender module has:

  • Five analog inputs with configurable triggers
  • Digital trigger
  • Built-in temperature sensor
  • Battery voltage measurement
  • Optional CR2032 coin cell holder
  • Optional pushbutton to manually activate data transmission

CONFIGURATION

Without any programming knowledge, the sender module can be configured to transmit:

  • On power up
  • When any analog input goes above a certain value
  • When any analog input goes below a certain value
  • When any analog input changes by more than a certain amount
  • Periodically from 1 second to 18 hours

Configuration is accomplished using a laptop or desktop connected via a standard FTDI serial cable.

LOW COST

The sender costs only $2.43 in parts (qty 1000) or $3.50 (qty 10). Think of all the things you can monitor at that price -- in the garage, basement, garden, kitchen, or bedroom.

LOW POWER

The sender uses only 18 µA on average. This means it can be installed in small places while running on a coin cell, or can be virtually maintenance free with a pack of AAs.

CONNECTEDNESS

The LoFi gateway listens to all of the senders and uploads the data to a PC or to the Internet. LoFi is compatible with data.sparkfun.com (aka Phant), a free open-source Internet repository. As demonstrated in the Semifinals video, you can connect LoFi to the Internet in under 2 minutes.

INTERFACE

The interface couldn't be more easy. On the sender, simply solder sensors to the standard 0.1-inch pitch holes. No programming necessary. On the PC, the software walks you through each connection step and lets you modify device configuration in a friendly UI.

Non-proprietary output means you can use all of the repository tools written for Phant (or for the JSON, XML, tab values it provides). The output from the Gateway to the PC is tab-delimited plain text, so you can log it in a terminal program or write your own software regardless of OS.

LEARN MORE

Battery Life Expectancy (1 year on coin cell, 10 years on AA)

Message Delivery Rate (>95% success rate)

Dealing with Static: Auto Gain Preamble and Error Correction

LoFi as a Solar-Powered Weather Station (temperature and light levels)

LoFi Detecting Garage Door State (tilt ball switch)

Artist Rendition of Productized Look and Feel (contest requirement)

Sender Schematic

Good Things Come in Small Packages (fitting into a pill bottle and iPhone charger)

Components
  • 1 × C1 Capacitor 10µF 16WV (CC1206ZKY5V7BB106)
  • 1 × IC1 Microcontroller, SOIC, ATtiny84A (ATTINY84A-SSU)
  • 1 × J1 Connector, 6-pin right-angle female socket (PPPC061LGBN-RC or 801-87-006-20-001101)
  • 1 × LED1 Status LED, 1210, bicolor (LTST-C155KGJRKT)
  • 2 × R1, R2 Current-limiting resistor, 220Ω 5% (RC1206FR-07220RL)
  • 1 × R3 Pull-down resistor, 100kΩ 5% (RC1206FR-7100KL or RK73B2BTTD104J)
  • 1 × J3 (optional) ISP6 programming header (75869-131LF)
  • 1 × Configuration cable FTDI USB-to-serial TTL 3.3V
  • 1 × Schottky diode SOD123 10V ultra-low drop (PMEG1030EH,115)

Project logs
  • Did I Leave the Stove On?

    a month ago • 0 comments

    Have you ever left the house and had that little voice in your head say “Did I remember to turn off the stove?" Or maybe you're concerned about a loved-one living independently. With LoFi, you can eliminate needless worry.

    Here is an example application where LoFi wirelessly monitors a stove using an adjustable heat detector. The steel casing is magnetically mounted so that it is out of the way, but does not require permanent installation.

    You can see this in action towards the end of the Semifinals video.

    TECHNICAL DETAILS

    Contactless temperature sensors provide an opportunity to instrument major appliances without opening or altering them. It is possible to connect a wireless transmitter to the LEDs on a modern oven display to determine if the stove is active. However, a less invasive technique is to simply measure the temperature externally using infrared.

    The Melexis infrared sensor (MLX90614) sees -70C to +380C. It is as simple as aiming the sensor at the stove top and measuring the temperature. LoFi transmits changes in the analog value, and can trigger transmissions on either those changes or a digital trigger pin.

    The Melexis thermal sensor can be read with either I2C or PWM (app note). LoFi is designed for analog inputs. To convert the Melexis PWM output to analog, attach a 10 kilohm resistor and 0.1 μF capacitor to the output pin.

    For user friendliness, I wanted an adjustable “on" threshold and an indicator light. Because only one input pin is needed by LoFi, it would have been cheapest, smallest, and easiest to modify the code to have LoFi's ATtiny chip perform the comparison operation and light the LED with the spare pins.

    For the sake of being a purist, I instead chose to create an interface board containing a comparator, so that LoFi would still be considered 'stock'. That is, this was an opportunity to document a solution for people that aren't comfortable with programming.

    The TLV3702 was chosen because it works down to 2.5 volts. C2 and R2 convert the IR sensor PWM to analog. R3 is the adjustment threshold for determining when the stove is 'on'.

    Below is the implementation of the circuit. Again, the comparator is only necessary if you don't want to modify the LoFi source code.

    There are a wide variety of interesting things to monitor in a home. With LoFi, the price is low enough to make it affordable.

  • You've Got Mail!

    a month ago • 0 comments

    A wireless mailbox notifier lets you know when the postal mail has arrived in your mailbox. This can be particularly helpful if your mailbox is not immediately adjacent to your front door.

    The mailbox notifiers I've seen usually rely on detecting when the mailbox lid is opened (hall effect sensor or tilt switch) or when a person approaches (motion sensor). Those are fairly successful methods -- but I didn't want to repeat what other people have already done. Also, those methods don't take into account whether mail is waiting or instead the homeowner simply triggered the lid sensor by anxiously checking their empty mailbox.

    Instead, I'd like to check for the presence of something in the box. A hacked postal scale would be highly effective, but would be awkward to fit. So, I'm going to use a reflected sensor: emit infrared light and measure the amount that returns. A white envelope or glossy magazine reflects significantly more light than an empty box. And, because LoFi transmits analog values, a threshold doesn't need to be tweaked between 'detect' and 'non-detect' states.

    Here's the schematic: (which is attached to LoFi)

    The 22 kilohm resistor forms a voltage divider with the phototransistor. A change in light (either due to sunlight entering due to the box being opened or due to reflection off of mail) changes the conductance of the phototransistor, and thus the division of voltage. That voltage is fed into a LoFi input.

    Two infrared emitters (LEDs) are placed in series with a current-limiting resistor to provide a light source. The second emitter is powered for 'free', as it simply uses power that otherwise would have been burned off in the resistor. On average, about 20 mA will flow.

    GREAT SCOTT!

    Twenty milliamps will drain the battery pack in less than a week! I thought LoFi was supposed to be low power?

    LoFi has a pin that provides GND only when the sensors are being read. Thus, when LoFi is sleeping (98% of the time), the emitters are off. Therefore, the AA pack will last years.

    For the case, I found some small plastic jars with colorful screw-on lids (Amazon B00523WBK2). This is attached with yellow Sugru.

    HOW WELL DOES IT WORK?

    As you can see below, the infrared reflective sensor detects mail very well. Over time, it will be interesting to see what different bunches of mail look like. “Either we just received a ton of mail, or one very glossy white envelope."

    I'm not sure why the detection increases slightly over time when staring at mail. Either the mail is settling or the phototransistor has both a fast and slow component to its detection properties. Perhaps it follows a curve like a capacitor?

    I did encounter one issue, which is that 433 MHz transmitter was completely shielded inside the metal box. I managed to snake the antenna out one of the bottom drain holes, after enlarging the hole slightly with a drill. Fair warning, you may need to seek permission from your spouse and homeowners association. ; )

  • Gateway

    a month ago • 0 comments

    The gateway listens to one or more senders and passes the data to a PC, or via WiFi to the intranet/Internet. This allows you to collect data locally or with a server.

    The gateway consists primarily of an Atmel ATmega328 microcontroller that reads the 433 MHz receiver and writes to the FTDI serial cable and CC3000 Wi-Fi board.

    Below you'll find the schematic. It begins with Schottky diodes for reverse battery protection and to allow multiple power source to be connected at the same time without affecting each other. This is followed by PPTC self-resetting circuit breakers for overcurrent protection. Finally, a Zener diode provides overvoltage protection. Because most people will only own one gateway, the extra cost of those protection parts is not a significant amount compared to an overall system.

    Notice that most of the pins are not connected to onboard components. Because the purpose of this board is to route messages, most of the pins lead to external connectors. Many spare pins are available, as this chip was selected for its speed, RAM, and surface-mount package.

    You can examine the PCB and Gerbers in the LoFi-PCB-Layouts.

View all 13 project logs

Build instructions
  • 1

    LoFi is expected to be delivered ready-to-use (prepopulated and preprogrammed). These instructions are for people that want to build LoFi themselves from scratch or are interested for curiosity. These instructions are expected to change as the project nears completion.

    Download and decompress the PCB layout files from this project page.

  • 2
  • 3

    Open the PCB layout folder and locate desired PCB you'd like to have made. For example, LoFi-PCB-Layouts/Sender/LoFi-Sender-v7.zip. Drag that zip file onto the OSH Park web page to upload it.

See all instructions

Discussions

lavaguava wrote 2 days ago null point

I agree with mikko.pihlajamaki this project would be extremely useful to the hobbyist. I hold the view that this project should have won the hackaday prize.

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mikko.pihlajamaki wrote 3 days ago null point

David,

Is there any hope that you might continue with the project? It shows so much potential.

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wifiwaves wrote 9 days ago null point

David,

Check your email...

Thanks...!

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wifiwaves wrote 10 days ago null point

Hmm...

I had a project in mind.

On to the next thing...

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tritospolemos wrote 13 days ago null point

Great project! When do we get to see some code? What [future] is that? ;-)
https://webcache.googleusercontent.com/search?q=cache:pLZn-h1luXoJ:https://hackaday.io/project/1552/instructions

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David Cook wrote 11 days ago null point

Hello Tritospolemos,

LoFi was created to compete in the Hackaday Prize contest. When LoFi was eliminated from the competition, I removed forward-looking statements related to the contest requirements. At this point, I'm not certain whether the project will be continued.

David

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mikko.pihlajamaki wrote 18 days ago null point

Hi David,

Excellent project! I hope you'll continue with it even you didn't make to the final five. I'm just waiting to fill my house with these things. (Have you considered using ESP8266 instead of CC3000 for _really_ low cost solution?)

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David Cook wrote 11 days ago null point

Thanks Mikko!

Well, the CC3000 is definitely more complicated than it needs to be. I hoped it would be as simple as passing in a URL and getting back a string of data. Instead, it needs a whole series of calls and a library to work. So, I may indeed look at replacing it with another solution, such as an ESP8266. At the higher end of the cost spectrum, I've been looking at the $99 Windows tablets (HP, Toshiba) to see if they could act as a touchscreen status panel and gateway simultaneously.

David

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radicalbiscuit wrote 18 days ago null point

David,

Congratulations on having made it as far as you did. I was really rooting for LoFi. I've enjoyed seeing your progress and I'm still excited about the future developments. I doubt my daily (nay, hourly) page refreshes will cease just because THP is over for LoFi.

If I could send you to space, I would! Instead, I'll just send you my goodwill.

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David Cook wrote 11 days ago null point

Hi radicalbiscuit,

Thank you for the kind words and support. One of the frustrating aspects of the contest is that they don't provide any feedback for improvement (which is ironic for a contest that espouses open ideals). So, I'm kind of scratching my head at this point.

Nevertheless, it was very exciting and I learned a lot. I have accumulated material that I intend to write up. However, now I don't have the contest deadlines driving me, I'll probably take time to bathe and sleep. : )

David

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tarzanbox wrote 22 days ago null point

Hi David,
Just wondering if it works as a network or in case of two nodes try to send at the same time, how would the central server handle that kind of situation and distinguish between each node ( MAC like thing available already??)

Good work.
Cheers.

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David Cook wrote 22 days ago null point

Hi tarzanbox,

Yes, each sender has a unique ID (like a MAC) and each message has a number. Therefore, you can use multiple gateways to support nodes sending at the same time in various zones in your house. The server can easily spot any duplicate messages that were heard by both receivers.

LoFi supports multiple channels (frequencies) as the transmitter and receiver are not hard wired. LoFi also delivers redundant messages to reasonably compensate for any losses or collisions.

David

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lavaguava wrote 24 days ago null point

Amazing! I want this, I have been looking for something similar to this for a while now. I saw this on your website. Good luck.

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David Cook wrote 24 days ago null point

I, too, was looking for low cost wireless instrumentation. The HackadayPrize ended up being a good excuse to try making it myself. : )

Thanks for reading Robot Room and for taking the time to support the project!

David

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Keegan Reilly wrote a month ago null point

Hi David, awesome work! Don't mean to rush you, you are making great progress, but I'm just curious when and where I might be able to start ordering ready made LoFi modules. Are you going to go through something like tinder or maybe sparkfun? I want to fill my house with dozens of temperature sensors and create an accurate thermal model of my insulation. The low cost of LoFi was the key to making something like that possible!

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David Cook wrote a month ago null point

Hi Keegan,

Thanks for the enthusiasm! This weekend I worked more on the configuration application and on an enhancement to improve serial synchronization across temperature ranges. I want to ensure that these are easy to set up and work reliably before making them available to others.

Timing until commercialization will depend on whether LoFi makes it into the finals. If so, I'll take some time off from my day job to accelerate LoFi development. Keep your fingers crossed.

David

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Patti Cale-Finnegan wrote a month ago null point

Good luck!

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David Cook wrote a month ago null point

Hi Patti,

Thank you! Keep your fingers crossed!

David

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Lesley Karasinski wrote a month ago null point

Amazing! Very best of luck David.

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David Cook wrote a month ago null point

Hi Lesley,

Thank you so much. I can't begin to express how much this support means to me.

David

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bcherni wrote a month ago null point

Congratulations! Awesome work, David! Good Luck! You have our vote! Did your spouse really let you drill a hole in the mailbox?!

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David Cook wrote a month ago null point

Shhh! I don't think she reads the log entries and she hasn't yet noticed the enlarged hole.

Thanks for the support!

David

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Nat wrote a month ago null point

Very cool. Good luck!

Are you sure? [yes] / [no]

David Cook wrote a month ago null point

Thank you for the positive energy -- there is less than a week to go and I'm exhausted. : )

David

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bak_jess wrote a month ago null point

Hi David - Amazing work! Best of Luck. Jessica (Rachel's sister)

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David Cook wrote a month ago null point

Hello Jess!

Do you think that Rachel is a little bit toooooo supportive of sending me into space?

David

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jsjcfeltz wrote a month ago null point

Good Luck on your entry!
You are an inspiration to the BHS Robotics team!

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David Cook wrote a month ago null point

Wow! That is very kind of you to say. I really appreciate the support. Go BHS!

David

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JTL wrote a month ago null point

Nice! Wondering if I can use this to detect someone trying to "jimmy" a door open...

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David Cook wrote a month ago null point

Yes, Adafruit has a vibration sensor that is essentially a spring with a wire inside of it. Vibration causes the spring to make contact with the wire, which would trigger LoFi to send a signal. This would also detect knocking and someone breaking a window.

https://www.adafruit.com/products/1766

Hope this helps!

David

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Noam Rathaus wrote 2 months ago null point

Can you explain your comment in the Readme file?
"This is the first prototype board which is missing some pulldowns and minor improvements. (The revision is not done yet.)"

What is missing? and what improvements?

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David Cook wrote 2 months ago null point

Hi Noam,

Sure! Here are the changes I've made since v1 of the listener (gateway):

1. Changed to surface mount power connector and ISP6 for improved manufacturability.

2. Diode and current limiting resistor on the CC3000 WiFi interface between IRQ and the MCU, and between MISO and the SPI bus. This is because the CC3000 is a 3.3V part but the 433 MHz receiver and MCU are running at 5 V.

3. Directly connected the CC3000 regulated 3.3 V to VBEN (rather than using a pullup) because the breakout board does not level shift this input (grrrrr) and the WiFi board will always be active when attached.

* Added another LED to indicate full message received as opposed to simply incoming bits.

* Added external connectors for all of the LEDs so that the board can be placed inside an enclosure.

* Added PPTC self-resetting circuit breakers to each source of power input for overcurrent protection.

* Added 5.6 V zener diode for overvoltage protection.

* Added a test hook voltage input from the AVR Dragon, since it doesn't provide voltage through the ISP6 interface that the good ol' STK500 board did.

* Added spare 0.1 uF and 10 uF capacitor pads.

* Added a spare power input for bench power supplies.

* Added an RX test point so I can see incoming bits on the oscilloscope.

I'll update the published schematics and PCB files soon.

David

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David Cook wrote 2 months ago null point

Hi Noam,

As promised, the schematic and PCB files have been updated and posted.

David

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BJK wrote 2 months ago null point

Good luck, David! I like that you get to continue refining your project throughout the stages of competition. Alles Gute!

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David Cook wrote 2 months ago null point

Danke vielmals!

I seem to be going in two opposing directions: smaller and larger. 'Smaller' to fit into novel locations and 'larger' to offer easier prototyping. I have a couple of really interesting applications in progress, which I'll publish before the next deadline.

David

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wifiwaves wrote 2 months ago null point

Congratulations for making the cut to the next level, David.

Onward and upward...!

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David Cook wrote 2 months ago null point

Thank you!

I spent most of Monday clicking the refresh button. I was overjoyed when the list appeared with LoFi on it. Then, almost immediately, I realized I would need to step up my game to compete with some of the other semifinalists. It will be an exciting, busy, and swift month.

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Rjpope42 wrote 2 months ago null point

Great project and great idea, I must admit I'm jealous it wasn't mine :)

I would be building some right now, but I'm not clear on something, it looks like the reciever boards are made, but you haven't worked out the reciever code?

Unfortunatley I don't have any other 433MHz recievers laying around to do the job

Again, great project and good luck!
It's nice to see something this useful and practical!

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David Cook wrote 2 months ago null point

Thank you for the compliments on the project! The receiver firmware is currently able to receive the message, decode the hamming, and pass the message to the PC. The PC is able to indicate the message arrived and log it to a file. However, the receiver and PC need to programmed to perform that task through Wi-Fi. Also, the PC software needs to be able to show all of the senders on a site map and let you view the messages on the screen. So, there is definitely work to complete -- but I believe there is enough time to do so.

I appreciate your kind words and support!

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Jasmine wrote 3 months ago null point

Hello David, I've just checked your project and it meets the requirements, so it will be considered for the next round of The Hackaday Prize. Thanks & good luck.

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David Cook wrote 2 months ago null point

That's wonderful news! I see you and the team seem to be double-checking all 400+ projects. Based on their replies, some builders are grateful, some seem to have abandoned their projects, and a few seem to be giving you attitude. Therefore, in case anyone else doesn't say it: Thank you, Jasmine. You're efforts to help everyone across the starting line is truly decent.

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TacticalNinja wrote 3 months ago null point

Hi David,

I've been fascinated by, and learned so much from your work since robotroom.com (I've been reading it since I was 16! I remember sending you an email regarding an H-Bridge design back then.)

I got a question though, I'm not sure if I missed something from your write up, is it possible to have a few of those transmitters transmitting at the same time with one receiver node? If so, how did you manage to receive the signal simultaneously? TIA, I'll keep posted.

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David Cook wrote 3 months ago null point

Hello TacticalNinja -- I have had a lot of fun writing up articles over the years. I'm glad you've enjoyed reading them!

Yes, LoFi supports multiple transmitters for a single receiver. But, as you suspect, it is not possible for a single receiver to receive messages from more than one transmitter on the same frequency at literally the same time. Instead, the system relies on two important conditions:

1. The transmitters are low duty cycle, meaning they spend most of the time being quiet (which also extends battery life).

2. The transmitters repeat data (retries) at slightly uneven intervals to avoid overlap of all of the messages.

I've found this works really well. For more congested conditions, you can use multiple receivers at different frequencies.

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TacticalNinja wrote 3 months ago null point


Hi David,

Thanks for the quick reply. I was also thinking of the same mechanism since I could not find any other way to sort out multiple transmitter nodes using a single receiver node without some sort of ACK signal.

Keep those projects coming! :-)

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Eric Tsai wrote 3 months ago null point

David, we have pretty similar projects. Your MCu design is a lot more battery efficient than mine. I've been using several AA batteries to keep mine running. I'll have to investigate your ATtiny design to see if I could incorporate it into my Arduino sensor node design.

Thanks for the inspiration! I linked your project in my hackaday.

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David Cook wrote 3 months ago null point

Hi Eric -- Thank you. You sure have a wide variety of monitoring ideas on your project page!

I'm using the deep sleep mode with a watchdog interrupt to wake up, if that helps you any. The sensors are powered down until they are read, and my board doesn't use a voltage regulator. So, that definitely keeps current usage to a minimum.

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Minimum Effective Dose wrote 3 months ago null point

I love the concept behind this project, it's fantastic. I'm very excited to see how it develops. Really sharp work.

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David Cook wrote 3 months ago null point

Thank you so much! The listener + receiver + WiFi board (effectively becoming a LoFi hotspot) has just been finished. After the boards arrive I'll post pictures.

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radicalbiscuit wrote 3 months ago null point

I'm excited at the prospects this offers. I've preemptively purchased a few receiver-transmitter pairs and I anxiously await availability.

Two questions, and I must apologize for the first:

When might these be mass produced and available to an end user like me?

What am I supposed to do with all these extra receivers? :P Maybe I can set up multiple receivers for a wider range.

Thanks for your work! I'm most excited about two projects in the world right now: ISEE-3 and this.

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David Cook wrote 3 months ago null point

Hello radicalbiscuit,

Thank you so much for the kind words. It is very motivating when someone posts a positive comment like yours!

1. I've been approached by a wonderful reseller about producing the product. But, I need to finish it first. I'm working on the listener board now (up to this point, I've been using a sender board in reverse.) I can't tell whether it would be viewed positively or negatively by the judges for a product to be 'in stores' before the conclusion of the contest.

2. Ha! I also have a bunch of extra receivers. Whenever I dig in my parts container for a transmitter module, I have to toss a couple of receivers back. Nope. Nope. Yes! Maybe you should start a project called 'Triangulation Using Spare AM Receivers'.

David

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radicalbiscuit wrote 3 months ago null point

While this wouldn't solve the problem of extra receivers, it would utilize transmitters and receivers in pairs: have you considered meshing, standalone Lofi repeaters? The purpose being, of course, to extend range of the system indefinitely.

Similar to APRS, when an error-free message is heard by a receiver/repeater and has not yet been received before, it will transmit the same message, perhaps altered to indicate the number of hops the message has taken. Other repeaters will also transmit the message and in the end, the master receiver picks it up.

This could be well-suited to a wall wart form factor, although wireless functionality may also work well if your receiver commands power efficiency in the same neighborhood as your transmitter.

And there's no reason these couldn't double as the triangulation devices mentioned in your reply to my original comment. Given known locations of the repeaters, a plot of all the Lofi senders on OpenStreetMap is only a calculation away... :D



Once again, thanks for your work. Looking forward to seeing and reading about the new boards!

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David Cook wrote 3 months ago null point

Range hasn't been an issue so far, however you are definitely on to something regarding making a basic mesh network. If you consider a far away or terrain-constrained transmitter at only 3V, a repeating receiver with a 12 V transmitter and nicer antenna could significantly broaden the total network range without adding much cost. Good idea!

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Pixel Pirate wrote 4 months ago null point

Sorry if I'm being OCD, but those traces on your PCB make me cringe...

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David Cook wrote 4 months ago null point

Someone once said, "It should be 'CDO', because then it would be in alphabetical order". But seriously, I'm always open to suggestions. What would you do differently? The Copper Connection file is listed in the downloads. Could you make some sample edits and send the file to me?

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Pixel Pirate wrote 3 months ago null point

Mostly it's just aesthetics cringe. I can't stand routing a trace that isn't a 45 degree angle. Nor can I stand uneven spacing.
IT's just a psychological thing.

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Ron wrote 4 months ago null point

Nice project Mike, wireless and ATtiny is the way to go

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David Cook wrote 4 months ago null point

Thanks Ron. Yes, the ATtiny has so many built-in features that this project needs: oscillator, deep sleep, long-period watchdog wakeup, voltage reference, temperature sensor, EEPROM for settings, and so on.

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wifiwaves wrote 4 months ago null point

David,

Just something for everyone to be aware of...

The FCC has specific requirements for using transmitters. The FCC has made provisions for unlicensed transmitters throughout the radio spectrum. You can operate just about anywhere, but there are restrictions on the field strength, type of emission, and duty cycle that the system designer needs to be aware of before planning and deploying a system.

Unlicensed transmitters are covered under Part 15. The specific section covering these particular transmitters is at:

http://tiny.cc/a519hx

Briefly, the transmitters under discussion in your project are limited by two provisions:

15.231 (a)

The transmit on time is limited to a maximum of 5 seconds. Video, voice, and control of toys is prohibited, and the transmitter must be manually triggered. No periodic operation is allowed, except to verify system operation. In this case, the transmit time is limited to 2 seconds per hour (1/1800 duty cycle).

15.231 (e)

The on-time is limited to a maximum of 1 second. The off-time shall also be at least 30 times the on time, with no less than 10 seconds between transmissions. The key to using this section is to have the system transmit in short bursts, with a 10 second off time. No restriction on application or modes, but you have to pay attention to the duty cycle.

I ran into these issues when I was designing a remotely located turbidity sensor protecting a surface drinking water supply. Our design accommodated these requirements with no particular impact on the device functionality. We are using this long range device:

http://tiny.cc/lg39hx

It should be noted that where the device performs a fire, security, or other life safety function, the device may transmit for the entire duration of the alarm condition. While not prohibited, one should give due consideration to using homebrew devices in such situations. Commercial devices are rigorously tested under numerous circumstances to insure that they will operate properly when necessary.

Good RF design practice guidelines (aside from the FCC requirements) 'require' that a transmitter not use more power than is necessary to accomplish the given communication. This keeps the spectrum cleaner, and allows greater density. It also keeps the power supply requirements lower.

While these transmitters may not be seen at any great distance, following these limitations keeps one from having 'interesting' discussions with the FCC.

Onward and upward...!

wifiwaves

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David Cook wrote 4 months ago null point

This is great information. You clearly have the voice of experience. : )

At present the duration of messages is 200 ms. I'll make the default configuration include a quiet period of 10 seconds.

Fortunately, LoFi is not tied to a specific transmitter, frequency, or antenna. So, it will be possible to select appropriate modules for a region, governing body, or interference profile.

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wifiwaves wrote 4 months ago null point

David...great work!

For those interested in these kinds of transmitters/receivers, here are a ton of devices out there. Search for "key fob remote control" and a plethora of transmitters & receivers will show up. There are a couple of other bands available, most notably 418MHz (with little interference).

I find this device to be extremely helpful when working with these kinds of devices:

http://www.iautomate.com/products/rf-explorer-433-mhz-spectrum-analyzer.html

No pecuniary interest...just a fine device for cheap.

Keep up the great work!

wifiwaves

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David Cook wrote 4 months ago null point

Hi wifiwaves,

Hmmm. 418 MHz sounds very appealing. Thus far, I haven't had problems with interference in my home, but surely other people will. This would give people a choice. Also, perhaps I could build listener that could connect to two receivers, thus permitting more devices.

Thanks for the tip!

David

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Dave Jakopac wrote 4 months ago null point

David, the Sandwich robot I built--based on your book--still runs in demos at Chibots events. Great project and I'm looking forward to seeing the results.

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David Cook wrote 4 months ago null point

Hi Dave!

On a recent family vacation, we played a game where we were asked about our most prized personal position. I said 'Sandwich' and my family looked at me like I was crazy. Sure, there's epoxy coming out the coupler, ratty wires, and a few cuts that went slightly too far, but it still works and I built it myself. So, I am sincerely pleased to hear your robot is still running as well.

David

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barcellos.alvaro wrote 4 months ago null point

Slow and secure and constant as into the Voyager. My vote sure.
Could open a trend in remote control and sensors.

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David Cook wrote 4 months ago null point

According to Wikipedia, Voyager has a bit rate of 40 bits/s without error correction. So, I'm pleased to have 1970's technology beat. Oh, wait, it can transmit up to 115.2 kbit/s? Never mind.

Thanks for the vote!

David

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Mike Gordon wrote 4 months ago null point

This looks great! I can think of multiple uses around the house for a few of these. With that said, how about adding a 1-byte transmitter identifier character to the header to allow for independent sender/transmitters to be used in the same environment? The identifier could be set in the same interface as the trigger parameters.

It doesn't show in the project, but are you also planning a corresponding output module to plug into the 433 receiver? I'm thinking a small board that would read the transmission and duplicate the states out to corresponding analog and digital pins, either momentary, or latching until a new transmission is received that would change a pin's value, or even for a user configurable (on the output board) number of milliseconds

What is the power consumption of the input board and transmitter combination at rest and while transmitting? One application I'm thinking of would be to send an alert when one of 3 doors opens and closes, possibly with a status update on one every 10 mins. I'd like to power it off of a couple AA batteries, but not if I'd have to change them every couple weeks. Any ballpark estimate on that?

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David Cook wrote 4 months ago null point

Hi Mike,

Currently the header is six bytes and contains:
'L', message length, sender address, message id + retry id, command, subcommand

Therefore, yes!, you can have many transmitters. Also, note the message length byte and command bytes will permit the receiver to be able to deliver a variety of messages that it doesn't know anything about (forward compatibility).

As for the receiver, I am presently using a LoFi sender configured 'backwards'. But, I plan to make a special board to permit direct uplink to WiFi.

As for power consumption, I just added a log post inspired by your question. The answer is: a couple of AAs would power the device for a decade.

David

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João Lucas Torres wrote 4 months ago null point

Great work! I really love low cost networks. I'm finishing my final course project and it's about infrared networks.

Waiting news of this project.

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David Cook wrote 4 months ago null point

Thank you for the encouragement. New boards arrived today, so I'll have interesting material to post this weekend.

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Hjorgenogueira wrote 4 months ago null point

what a great project David, i always thought simple RF without complicate and expensive protocols like zigbee and other would do the trick most of the times...i think i will try to make one of these just to try out, unless if you have already spares ones and are planing to sell these...?!
thanks for the inspiration and sharing with us!

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David Cook wrote 4 months ago null point

Thank you! When the project nears production quality, I'll remember to upload an object file as well, so that you can program bare chips without having to reproduce the compiler environment. That being said, I am optimistic that the ready-to-run modules will be manufactured and available from our favorite sellers.

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Neal McBurnett wrote 2 months ago null point

The cool thing about 802.15.4 and stuff like zigbee that builds on it is that besides being a standard, and super-low-power, it can also fit in to a standard homenet, and be addressable securely and globaly via ipv6 (6lowpan). Can you contrast your solution with a cheap, bare-bones 802.15.4 solution in terms of cost, etc?

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David Cook wrote 2 months ago null point

The XBee module is wonderful and much more powerful.

However, LoFi is:
* Lower cost (about $2 in parts + $1 for the transmitter)
* Lower power (10 mA transmit, 13 uA idle)
* Smaller size

Both have their place. If you simply need something to monitor some analog values (sensors) and run a long time on a coin cell, then LoFi is a good choice. If you need a communication channel, then XBee is a good choice.

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DeepSOIC wrote 4 months ago null point

I want this one to go straight into our science lab!

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David Cook wrote 4 months ago null point

All right!

Your thumbnail freaked me out until I clicked on it.

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Mike Szczys wrote 4 months ago null point

Hi David! This already looks like a fantastic entry for The Hackaday Prize.

I actually stopped by to mention that I'm a huge fan of yours. Your book "Robot Building for Beginners" was the second book I read when beginning to learn about electronics and in my mind the most formative. Thanks so much for sharing your knowledge and passion!

Good luck with this entry.

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David Cook wrote 4 months ago null point

Wow! Thanks Mike. That means a lot to me. I visit Hack A Day daily to learn from others and to be inspired. Your site does so much to encourage science that I absolutely had to contribute an entry to your contest. By the way, I am really impressed with how easy it is to post and edit projects here.

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