Microcontrollers

2402 Articles

Raspis in Near Space

Throwing Pis Into The Stratosphere

November 14, 2014 by 26 Comments

It’s always exciting to see the photos from High Altitude Ballooning (HAB) outings. While it’s no surprise that the Raspi is a popular choice—low cost, convenient USB jacks, etc.—this is the first build we’ve seen that uses an OLED during the trip to show real-time data on-screen to be picked up by the on-board webcam. (Though you may have to squint to see it at the bottom middle of the above image).

[Fabrice’s] payload made it to 26,000m, and the screen he chose, an ILSOFT OLED, performed admirably despite the extreme conditions suffered (temperatures can reach -50C). The last time we saw a near-space Raspi payload was a couple of years ago, when [Dave Akerman] was closing in on UK balloon altitude records. [Dave] hasn’t stopped launching balloons, either, testing new trackers and radio modules, as well as his most recent build that sent a Superman action figure to the skies—all recorded in glorious HD.

Check out both [Dave] and [Fabrice’s] blogs for loads of pictures documenting the latest in High Altitude Ballooning, and stay with us after the jump for a quick video of [Fabrice’s] OLED in action.

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Adding A Battery Gauge To A Project With Zero Parts

November 8, 2014 by 41 Comments

The typical way of doing a low battery detector is throwing a comparator in the circuit, setting it to measure a certain threshold voltage, and sending that signal off to a microcontroller or other circuit to notify someone the battery is going dead. [Josh] has a simpler way using an 8-bit AVR and zero other parts.

The chip [Josh] is using is the ATtiny84. The ADC in this chip is usually used to measure an unknown voltage against a reference voltage. The trick [Josh] is using is to do this in reverse: The internal 1.1 Volt reference voltage is measured against an unknown scale, namely the input voltage.

The value provided by the ADC on the chip will always be Vin times 1024 over the reference voltage. Since Vin will be 1.1 V in this case, the ADC value is known, it’s only a matter of doing some 6th grade algebra to determine the value of the input voltage.

[Josh] put together a small demonstration where the chip blinks out the number of volts its receiving from a bench power supply. By blinking a LED, it can blink out the current value of VCC as integers, but by using this technique you should be able to get a fairly fine-grained reading of what VCC actually is. Video below.

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Triple Sensor Mailbox Alert Really Delivers

November 7, 2014 by 22 Comments

Messing with the U.S. Mail is not something we generally recommend. But if you build your own mailbox like [Bob] did, you stand a much better chance of doing what you want without throwing up any flags.

Speaking of throwing up flags, one of the coolest parts of this project is the toy mailbox inside the house that monitors the activity of the real box. When there is mail waiting, the flag on the toy mailbox goes up. Once [Bob] retrieves the mail, the flag goes back down automatically. A magnet in the real box’s flag prevents false alarms on the toy box provided the Flag Raised On Outgoing protocol is followed. Best of all, he built in some distress handling: If the mailbox door is left hanging open or the battery is low, the toy mailbox waves its flag up and down.

So, where do the three sensors come in? A magnetic reed switch on the wall of the real mailbox pairs with a magnet in the flag. To determine whether the door is open, [Bob] initially used another magnetic reed switch on the underside of the box. This didn’t work well in wet weather, so he switched to a mechanical tilt sensor. An IR LED on the ceiling and a phototransistor on the floor of the box work together to detect the presence of mail.

[Bob]’s homebrew mailbox has a false back that hides a PIC 16F1825. When the door opens, the PIC wakes up, turns on a MOSFET, and checks the battery level. It waits two minutes for the mailman to do his job and then reads the flag state. After comparing the IR LED and phototransistor’s states, it sends a message to the toy mailbox indicating the presence or absence of mail.

The toy mailbox holds a modified receiver board and a servo to control its flag. [Bob] has made the code and schematics available on his site. Walk-through video is after the jump.

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Using Router SoCs As WiFi Modules (Yet Again)

November 6, 2014 by 34 Comments

8-bit AVRs and 32-bit ARMs do one thing, and one thing well: controlling other electronics and sensors while sipping power. The Internet of Things is upon us and with that comes the need for connecting to WiFi networks. Already, a lot of chips are using repackaged System on Chips to provide an easy way to connect to WiFi, and the USR-WIFI232-T is the latest of the bunch. It’s yet another UART to WiFi bridge, and as [2XOD], it’s pretty easy to connect to an AVR.

The module in question can be had through the usual channels for about $11, shipped straight from China, and the only purpose of this device is to provide a bridge between a serial port and a wireless network. They’re not that powerful, and are only meant for simple tasks,

[2XOD] got his hands on one of these modules and tested them out. They’re actually somewhat interesting, with all the configuration happening over a webpage served from the device. Of course the standard AT commands are available for setting everything up, just like the ESP8266.

With a month of testing, [2XOD] has found this to be a very reliable device, logging temperatures every minute for two weeks. There’s also a breakout board available to make connection easy, and depending on what project you’re building, these could be a reasonable stand-in for some other popular UART -> WiFi chips.

A Development Board For The ESP8266

November 5, 2014 by 44 Comments

[Necromant] is ready to dip his toes into the world of firmware development for everyone’s favorite WiFi chip, the ESP8266. Before that begins, it would be a good idea to make a nifty little breakout board for this chip. Here it is, a board with a USB to UART converter with board art that’s compatible with a toner transfer process.

Since this is just a board that turns USB into something the ESP8266 can understand, the most reasonable course of action would be to throw an FTDI chip in there and call it a day. We wouldn’t suggest that. Instead, [necromant] is using a Prolific PL2303HX. The RTS/DTR pins on the serial chip aren’t used, but only because the ESP8266 forums haven’t yet decided on how to connect them to the WiFi chip. GPIOs on the Prolific are broken out for some other projects [necromant] has in mind, with a userspace driver to make everything work.

[Necromant] is the creator of Antares, a build system for microcontrollers and a Hackaday Prize entry. He intends to make his build system compatible with this WiFi chip, just as soon as everyone else figures out an easy way to make it work.

Using A Headphone Jack As A UART

November 4, 2014 by 38 Comments

We’ve seen audio ports being used to establish a communications channel between a computer and a microcontroller before, but nothing quite as slick as this. [Gordon] is using a webpage running on a tablet to send Javascript to a microcontroller where the entire program is interpreted.

[Gordon] is using the Espruino Pico, a board that’s on Kickstarter right now. This tiny board is built around a javascript interpreter, allowing code to be written and updated on the fly without mucking around with bootloaders.

This technique can be expanded to provide bidriectional communication between a microcontroller and a computer. On the project Github, [Gordon] used the microphone pin on a TRRS jack to sent data to a computer. It needs two more resistors, but other than that, it’s as simple as the one-way communications setup.

[Gordon] put together a few demos of the program, including one that will change the color of some RGB LEDs in response to input on a webpage.

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Checking Email With The ESP8266

November 3, 2014 by 29 Comments

Ever so slowly, everyone’s favorite WiFi adapter is making its way into Internet-enabled projects. [jimeer01] created a device that reads the subject and sender lines from the latest email in his inbox and displays it on an LCD using the ESP8266 WiFi chip.

[jimeer] is using a ByPic for writing to the LCD and querying an inbox through an ESP8266 module. The ByPic is a board built around the BV_Basic firmware, stuffing a PIC microcontroller in an Arduino form factor and giving it a BASIC interpreter. Because this board isn’t ‘compile and flash’ like an Arduino, it’s perfectly suited for changing WiFi configurations and IMAP server credentials on the fly.

The device grabs the latest email in an inbox and displays the date, sender, and subject on the display. After scrolling through those lines, the PIC hits the ESP8266 to query the server again, grabbing the latest email, and repeating the whole process again, all without needing to connect the device to a computer. Video below.

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