Arduino voltage measurement tricks

We think it’s a great learning experience to tear back the veil of abstraction and learn a bit more about the hardware found on an Arduino board. This project is a great example. [Scott Daniels] takes a look at the other voltage measurement options available to AVR chips used by Arduino.

If you’ve used the analogRead() function then you’ve already measured a voltage using the Arduino. But do you know what is going on behind the scenes to make this happen? The Analog to Digital converter on the AVR chip is being used to measure an incoming voltage by comparing it to a known voltage reference. That reference is by default the supply voltage line for the chip. This should be 5V but will only be as accurate as the regulator supplying it. [Scott] looks at the other voltage references that may be used. An external reference can be used by adding hardware, but that’s not the focus of his article. Instead he looks at using the 1.1V internal reference. He’s written some short example code that let’s you measure the incoming line voltage based on that internal reference. This is a very handy trick that can let you detect when the chips is running from a battery and how much juice is left in the cell.

Analog soil moisture alarm

The lion’s share of soil moisture monitors we see are meant as add-ons for a microcontroller. So we’re glad that [Miceuz] tipped us off about this soil moisture alarm he built with analog parts. It’s really not hard to take the concept and build it in the analog world. That’s because you’re just measuring a resistance value. But for those of us who never really got started with analog parts this is a great project to learn from.

A high-efficiency op-amp is doing the brunt of the work. When the soil is moist the resistance is rather low compared to a reference voltage provided by a separate resistive divider. But when the plant gets thirsty and the soil dries out the resistance increases, triggering the op-amp to illuminate an LED and create some noise on the buzzer (we’re a bit confused on how that buzzer works).

Unfortunately this isn’t a viable long-term solution as the battery calculations show it lasting only about four months. That’s where a microcontroller-based circuit really shines, as it can put it self in low-power sleep and wake infrequently to take readings.

Multi-channel analog input module is a good jumping-off point for many projects

[Scott Harden] has already produced some projects which measure analog inputs. But he’s got plans for more and wanted a base system for graphing analog signals. You can see the small board next to his laptop which offers the ability to sample up to six signals and push them to a PC via USB.

The ATmega48 and a few supporting components are all you’ll find on that board. The USB connection is taken care of by an FTDI cable. He went that route because the cables are relatively cheap, easy to come by, and already have driver support on all the major operating systems. If you look at the screen you can see a window graphing one analog input in real-time. He wrote this in Python (which is once again a cross-platform tool) and it has no problem graphing all six inputs at once.

This is immediately useful as an upgrade to [Scott's] ECG machine. His future plans include a Pulse Oximeter, EEG, and EEG.

You’ll throw your back out playing this analog TV synth

de-rastra

While CRT televisions fall to the wayside as more people adopt flat-panel TVs, the abundance of unused sets gives hacker/artist [Kyle Evans] an unlimited number of analog canvases on which to project his vision. He recently wrote in to share his latest creation which he dubs “de/Rastra”.

The “CRT Performance Interface” as he calls it, is an old analog television which he hacked to display signals created by moving the TV around. Fitted with an array of force sensors, accelerometers, and switches, the display is dynamically generated by the movements of whomever happens to be holding the set.

Signals are sent wirelessly from his sensor array to an Atmel 328 microcontroller with the help of a pair of XBee radios, where they are analyzed and used to generate a series of audio streams. The signals are fed into a 400W amplifier before being inserted into the CRT’s yoke, and subsequently displayed on the screen.

We’re sure [Kyle] is probably trying to express a complex metaphor about man’s futile attempts to impose his control over technology with his project, but we think it simply looks cool.

Check out [Kyle’s] work for yourself in the video below and give us your take in the comments.

[Read more...]

A new and improved magnetic cello

Over the past few months, [Magnetovore] has been working on his magnetic cell project. It’s a very interesting instrument that seems right out of the electronic music explosion of the 1970s. Now, he’s ready to share his invention with the world, and we wouldn’t be surprised if we see this instrument being picked up by a few avant-garde musicians in the next few years.

Last September, we were introduced to [Magnetovore]‘s magnetic cello. The original version used four ribbon sensors for each of the strings and had completely analog electronics, leaving us wondering why this cello wasn’t invented in the 70s. The new version of the cello keeps the analog electronics that sound remarkably like a real acoustic cello, but does away with three of the ribbon sensors. Now the cello has a single ribbon sensor being used as all four strings – to change which string is played, the musician just has to press a button on the ‘bow’.

There is a drawback to using only one ribbon sensor; it’s now impossible to play two strings simultaneously as on an acoustic cello. The electronics in [Magnetovore]‘s original magnetic cello were monophonic anyway, so we’ll chalk this design change-up to reducing component cost.

After the break, you can check out a trio of very talented cellists playing [Magnetovore]‘s magnetic cello. There’s the classic Pokemon Center theme, the Mario Bros. theme, as well a Bach minuet and a crazy improvisation showing off what the magnetic cello can do.

[Read more...]

Advent Calendar of Circuits

We missed 60% of it already, but luckily you can easily watch the back catalog of [Alan Yates'] 2011 Advent Calendar of Circuits. As with traditional Advent Calendars he’s got a treat for every day in December leading up to Christmas. Instead of chocolate, the treat is a video about a different electronic circuit.

We didn’t find a playlist link, but you can just head over to his YouTube channel as each day is clearly labelled in the video titles. He starts off with a current limiting voltage regulator. A couple of days later he busts out a metal detector that will be fun to play with. Day 7 brings an AM transmitter/receiver pair, and Day 12 illustrates a burnt-out Christmas light detecting tool which we’ve embedded after the break.

The sheer volume of projects he’s putting out every day is remarkable and delightful. He doesn’t even limit himself to one video a day, but has posted several ‘extra’ editions with quick, circuit demos. [Read more...]

This toy intercom system is way better than a pair of tin cans and some string

toy-intercom-system

On his blog, [Kenneth Finnegan] recently showed off a replica of a fun toy he used to play with as a kid, a telephone intercom system. The setup is pretty simple, requiring little more than a pair of analog phones, a battery, and a resistor.

The phones are connected to one another using a standard telephone cable, but [Kenneth] uses a 9v battery to introduce a small bias current into the loop, allowing the speakers at either end to hear one another. He also added a small LED into the circuit so that there is a visual indication as to when both handsets are off hook.

The setup is very simple at the moment, though [Kenneth] does have some ideas in mind to enhance his intercom system. He hopes to tweak the remote phone to ring when the local phone is picked up, among other things.

Telephone technology is nothing new, but for just a few dollars (or less) your kids can be entertained for hours as [Kenneth] was way back when.

Continue reading to see a short video overview of the phone system, and be sure to share your ideas for enhancing it in the comments section.

[Read more...]