Fail Of The Week: ESP Walkie, Not-So-Talkie

July 23, 2018 by Jenny List 51 Comments

The ESP8266 has become such a staple of projects in our community since it burst onto the scene a few years ago. The combination of a super-fast processor and wireless networking all on the same chip and sold in retail quantities for relative pennies has been irresistible. So when [Petteri Aimonen] needed to make a wireless intercom system for cycling trips it seemed an obvious choice. Push its internal ADC to sample at a high enogh rate for audio, and stream the result over an ad-hoc wi-fi network.

The result was far from satisfactory, as while early results with a signal generator seemed good, in practice it was unusable. Significant amounts of noise were entering the pathway such that the resulting audio was unintelligible. It seems that running a wireless network causes abrupt and very short spikes of power supply current that play havoc with audio ADCs.

He’s submitted it to us as a Fail Of The Week and he’s right, it is a fail. But in a way that’s an unfair description, because we can see there is the germ of a seriously good idea in there. Perhaps with an external ADC, or maybe with some as-yet-to-be-determined filtering scheme, an ESP8266 walkie-talkie is one of those ideas that should be taken to its conclusion. We hope he perseveres.

A Super Simple ESP8266 IOT Motion Sensor

July 19, 2018 by Tom Nardi 31 Comments

It’s really hard to overstate how awesome ESP8266 development boards like the Wemos D1 Mini really are. For literally a couple of dollars you can get a decently powerful Wi-Fi enabled microcontroller that has enough free digital pins to do some useful work. Like the Arduino and Raspberry Pi before it, the ESP8266 is a device that’s opening up whole new areas of hacking and development that simply weren’t as practical or cost-effective as previously.

As a perfect example, take a look at this stupendously simple Internet-connected motion detector that [Eric William] has come up with. With just a Wemos D1 Mini, a standard PIR sensor, and some open source code, you can create a practical self-contained motion sensor module that can be placed anywhere you want to keep an eye on. When the sensor picks up something moving, it will trigger an IFTTT event.

It only takes three wires to get the electronics connected, but [Eric] has still gone ahead and provided a wiring diagram so there’s no confusion for young players. Add a 3D printed enclosure from Thingiverse and the hardware component of this project is done.

Using the Arduino Sketch [Eric] has written, you can easily plug in your Wi-Fi information and IFTTT key and trigger. All that’s left to do is put this IoT motion sensor to work by mounting it in the area to be monitored. Once the PIR sensor sees something moving, the ESP8266 will trigger IFTTT; what happens after that is up to you and your imagination. In the video after the break, you can see an example usage that pops up a notification on your mobile device to let you know something is afoot.

With its low cost and connectivity options, the ESP8266 is really the perfect platform for remote sensing applications. Though to give credit where credit’s due, this still isn’t the simplest motion sensor build we’ve seen.

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Shoehorning A Slick Spotify Remote Into An ESP8266

July 11, 2018 by Kerry Scharfglass 9 Comments

In 2017 Spotify finally deprecated their public vanilla C SDK library, libspotify, and officially replaced it with dedicated SDKs for iOS and Android and this new-fangled web thing we’ve all heard so much about. This is probably great for their maintainability but makes writing a native application for a Linux or a hardware device significantly harder, at least without an application process and NDA. Or is it? Instead of using that boring slab of glass and metal in their pocket [Dani] wanted to build a handy “now playing” display and remote control interface but was constrained by the aforementioned SDK limitations. So they came up with a series of clever optimizations resulting in the clearly-named ESP8266 Spotify Remote Control.

The Spotify Remote Control has a color LCD with a touchscreen. Once attached to a Spotify account it will show the album art of the currently playing track (with a loading indicator!) and let you play/pause/skip tracks from its touch screen, all with impressively low latency. To get here [Dani] faced two major challenges: authorizing the ESP to interact with a user’s Spotify account, and low latency LCD drawing.

If you’re not on iOS or Android, the Spotify web API is the remaining non-NDA’d interface available. But it’s really designed to be used on relatively rich platforms such as fully featured web browsers, not an embedded device. To that end, gone are the days of asking a user to enter their username and password in a static login box, the newer (better) way is to negotiate for a per-user token (which is individually authorized per application), then to use that to authenticate your interaction. With this regime 3rd party applications (in this case an ESP8266) never see a user’s password. One codified and very common version of this process is called OAuth and the token dance is called a “workflow”. [Dani] has a pretty good writeup of the process in their post if you want more detail about the theory. After banging out the web requests and exception handling (user declines to authorize the device, etc) the final magic ended up being using mDNS to get the user’s browser to redirect itself to the ESP’s local web server without looking up an IP first. So the setup process is this: the ESP boots and displays a URL to go to, the user navigates there on a WiFi connected device and operates the authorization workflow, then tokens are exchanged and the Remote Control is authorized.

The second problem was smooth drawing. By the ESP’s standards the album art for a given track at full color depth is pretty storage-large, meaning slow transfers to the display and large memory requirements. [Dani] used a few tricks here. The first was to try 2 bit color depth which turned out atrociously (see image above). Eventually the solution became to decompress and draw the album art directly to the screen (instead of a frame buffer) only when the track changed, then redraw the transport controls quickly with 2 bit color. The final problem was that network transfers were also slow, requiring manual timesharing between the download code and the display drawing routing to ensure everything was redrawn frequently.

Check out [Dani]’s video after the break, and take a peek at the sources to try building a Spotify Remote Control yourself.

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Morphing Digital Clock Will Show You A Good Time

July 10, 2018 by Kristina Panos 27 Comments

A few weeks ago, [HariFun] set out to emulate a 7-segment display with an LED matrix. Seems easy enough, right? Right. He also wanted to come up with a new way to transition between digits, which is a much harder task. But he did it, and it’s really cool. At a viewer’s suggestion, [Hari] used the transition as the basis for a mesmerizing clock that brings the smooth sweep of an analog second-hand into the digital age.

This is the coolest way to watch the time pass since the hourglass. You can almost hear the light move as one digit slides into the next. Each transition is totally unique, so depending on the digit this involves one or more vertical segments sliding from right to left, or multiple segments moving in a counter-clockwise circle.

You too can watch time glide by with little more than a 64×32 RGB LED matrix, a NodeMCU, and [Hari]’s digit transition code. It only costs about $25 to build, and you really can’t beat the quality of instruction he’s put together. Take a second or two and check it out after the break.

If you prefer OLEDs and vertical transitions, there’s a clock for that, too.

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Junk Bin Self Balancing Bot With ESP8266

July 5, 2018 by Tom Nardi 10 Comments

As we all know, sometimes the projects we plan simply never materialize. You have an idea, maybe even buy some of the parts you need, and then…nothing. Maybe you changed your mind, or maybe the idea was never that good to begin with. In any event, time marches on, the parts pile up, and the ideas come and go. Such is the life of the hacker.

[Andrius Mikonis] writes in to tell us how his graveyard of abandoned projects ended up providing exactly what he needed to embark on a project he’s been fascinated with for years: the two-wheel self balancing robot. He started with a motor and wheel set that was originally intended to be part of a rover, added an accelerometer, and tied the whole thing together with an ESP-01 he had lying around. The final result certainly looks the part, and goes to show that projects don’t always need to be 1000 hour labors of love to accomplish their goals.

The construction of this little bot is simple in the extreme. A piece of plywood makes up the primary structure, with the wheels glued to the bottom and the electronics taking up residence in the top. It’s powered by two lithium battery cells that were salvaged out of an old laptop, with a DC-DC buck converter to provide a stable 3.3 VDC for the ESP-01 and MPU6050 accelerometer. To control the motors themselves, [Andrius] is using a cheap L293 controller that he found on eBay.

For interactive control, [Andrius] is making use of the ESP’s Wi-Fi to provide a web-based interface. This lets you control the bot from essentially any device that has a browser, rather than having to use a dedicated hardware transmitter.

Self-balancing robots of various levels of complexity are a relatively common project in the hacker world. There’s just something magical about the way they scoot around, seeming to defy gravity.

ESP8266 Keeps Tabs On The Kid’s Tablets

July 5, 2018 by Tom Nardi 24 Comments

Assuming you have a child and it’s no longer womb-bound, there’s a fairly high chance they’ve already had some experience with the glowing beauty that is the LCD display; babies of only a few months old are often given a tablet or smartphone to keep them occupied. But as the child gets to the age where they are capable of going outside or doing something more constructive, staring slack-jawed and wide-eyed at their tablet becomes a concern for many parents.

[Richard Garsthagen] is one such parent. He wanted a way to monitor and control how much time his children were using their iPad, so he came up with an automated system based on the ESP8266. Not only does it keep track of how long the tablet is being used, it even includes a reward system which allows the parent to add extra usage time for good behavior.

At the most basic level, the device is a sort of “holster” for the child’s tablet. When the tablet is placed in the slot, it presses a microswitch at the bottom of the cavity which stops the timer. When the switch is open, the LED display on the front of the device counts down, and the ESP8266 pushes notifications about remaining time to the child’s device via IFTTT.

Time can be added to the clock by way of RFID cards. The cards are given out as a reward for good behavior, completion of chores, etc. The child only needs to pass the card in front of the system to redeem its value. Once the card has been “spent”, the parent can reset it with their own special card.

It’s a very slick setup, making perfect use of the ESP8266. Reading the RFID cards, updating the timer, and using IFTTT’s API keeps the little board quite busy; [Richard] says it’s completely maxed out.

You might be wondering what happens when the clock reaches zero. Well, according to the video after the break…nothing. Once the time runs out, a notification simply pops up on the tablet telling them to put it away. Some might see this as a fault, but presumably it’s the part of the system where humans take over the parenting and give the ESP8266 a rest.

This isn’t the first time we’ve seen a microcontroller used to get the little hackers on schedule. At least (so far) none of them have gone full Black Mirror and started tracking when the kiddos are watching it.

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Move Aside Mercury: Measuring Temperature Accurately With An RTD

June 28, 2018 by Sean Boyce 40 Comments

Temperature is one of the most frequently measured physical quantities, and features prominently in many of our projects, from weather stations to 3D printers. Most commonly we’ll see thermistors, thermocouples, infrared sensors, or a dedicated IC used to measure temperature. It’s even possible to use only an ordinary diode, leading to some interesting techniques.

Often we only need to know the temperature within a degree Celsius or two, and any of these tools are fine. Until fairly recently, when we needed to know the temperature precisely, reliably, and over a wide range we used mercury thermometers. The devices themselves were marvels of instrumentation, but mercury is a hazardous substance, and since 2011 NIST will no longer calibrate mercury thermometers.

Luckily, resistance temperature detectors (RTDs) are an excellent alternative. These usually consist of very thin wires of pure platinum, and are identified by their resistance at 0 °C. For example, a Pt100 RTD has a resistance of 100 Ω at 0 °C.

An accuracy of +/- 0.15 °C at 0 °C is typical, but accuracies down to +/- 0.03 °C are available. The functional temperature range is typically quite high, with -70 °C to 200 °C being common, with some specialized probes working well over 900 °C.

It’s not uncommon for the lead wires on these probes to be a meter or more in length, and this can be a significant source of error. To account for this, you will see that RTD probes are sold in two, three, and four wire configurations. Two-wire configurations do not account for lead wire resistance, three-wire probes account for lead resistance but assume all lead wires have the same resistance, and four-wire configurations are most effective at eliminating this error.

In this article we’ll be using a 3-wire probe as it’s a good balance between cost, space, and accuracy. I found this detailed treatment of the differences between probe types useful in making this decision.

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