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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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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!


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


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.


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.


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.


The LoFi gateway listens to all of the senders and uploads the data to a PC or to the Internet. LoFi is compatible with (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.


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.


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)

  • 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)

  • Did I Leave the Stove On?

    David Cook09/28/2014 at 20:05 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.


    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!

    David Cook09/17/2014 at 04:39 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.


    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.


    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

    David Cook09/17/2014 at 02:59 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

  • 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/ Drag that zip file onto the OSH Park web page to upload it.

View all 16 instructions

Enjoy this project?



voy.ager wrote 6 days ago point

Wow ! What a lot of work for just faking around. Project looks good but i believe this never worked and never had a chance. If it really worked, there should be no problem publishing the working Source codes if it is declared as Open Source. There are lot of mysteries in the Net.

  Are you sure? yes | no

Jorge Fabre wrote 04/14/2016 at 04:02 point

I just came across this project. I am really interested but reading the comments below I'm hesitant to continue as the source code is no where to be found. David would you kindly help us with this. 

Thanks for your great work. 

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Dylantje wrote 02/27/2016 at 17:26 point


Is this project still alive??? [ looks great/simple..

Is there a simple how to for a dombo like me?

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John Chiasson wrote 01/14/2016 at 15:23 point

I'm interested for home automation as well.  Anyone know if the boards are available, or if there is any source that will build them inexpensively?

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Nits wrote 01/11/2016 at 05:32 point

by when this is available?

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Indigaz wrote 07/03/2015 at 03:33 point

I too would like to add to the chorus of those interested in this project and would greatly appreciate the opportunity to use the source code as a learning tool.  I'm doing my best to learn microcontroller programming and seeing how someone achieves a task is the best way for my brain.  When I first saw this project during the first HaD prize and after seeing these things(transmitter/receivers) all over eBay for cheap, I was elated.  

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alon24 wrote 06/28/2015 at 08:50 point

Hi, can you share the code? 

This might be ported to Just an esp8266.

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Avamander wrote 07/17/2015 at 11:48 point

Try NRF24L01+ instead. Also, this project has been abandoned, it is kinda sucky that as soon as the person found out that he did not win, he abandoned the project. 

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Edoardo wrote 06/03/2015 at 18:38 point


This is seriously awesome, well done!!

But, as the others, I too would like to see the sourcode! Could you please put it in a repository or link us there?


  Are you sure? yes | no

tomg09 wrote 05/23/2015 at 19:38 point

I understand this project is shut down...but would you be willing to post the code you have somewhere?  Anywhere?  You don't have to maintain it, just post it so others can continue your work.

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Ken Burgess wrote 04/15/2015 at 06:34 point

This project is too cool for school, this should be a product/tool for the Arduino enabled.

Is there a plan to supply finished modules? I do SLS production 3D printing, would volunteer to do some packaging...

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Roger Guess wrote 04/03/2015 at 15:26 point

David, I just found this project. Amazing. If you have a desire to continue. I believe quite a few of us would support you.

  Are you sure? yes | no

Mohamed Nuwaos wrote 01/26/2015 at 03:13 point

this seems to be very cool gadgets,thanks for sharing, pls let me know where to buy the circuit board,or the transmitter. only Sri lankan following you haha

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mikko.pihlajamaki wrote 01/05/2015 at 08:47 point

It would seem that this project is killed and buried.

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Elliot Williams wrote 11/01/2014 at 21:20 point
Seriously great implementation and documentation, Dave. You shoulda won, IMO.

(Fan of the Robot Room from waaaaay back, FWIW. Thanks.)

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lavaguava wrote 10/29/2014 at 18:56 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 10/28/2014 at 08:30 point

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

  Are you sure? yes | no

wifiwaves wrote 10/22/2014 at 23:35 point

Check your email...


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wifiwaves wrote 10/21/2014 at 19:19 point

I had a project in mind.

On to the next thing...

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tritospolemos wrote 10/18/2014 at 06:54 point
Great project! When do we get to see some code? What [future] is that? ;-)

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David Cook wrote 10/20/2014 at 12:46 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.


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mikko.pihlajamaki wrote 10/14/2014 at 05:55 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?)

  Are you sure? yes | no

David Cook wrote 10/20/2014 at 12:50 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.


  Are you sure? yes | no

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