Ahh, the Lite Brite.

What could be more fun than pushing dozens of little plastic pegs through a piece of black paper in order to create a pixelated, though colorful image? Well, I can think of quite a few things more engaging than that, and luckily so can [Lonnie Honeycutt] over at MeanPC.

While contemplating what to build with a pile of LEDs, his daughter came into the room with her portable Lite Brite. He thought that the pegs she was using looked awfully similar to the LEDs on his desk, so he did some test fitting and was surprised to see that they fit almost perfectly.

[Lonnie] thought that the toy would make an excellent clock, and his daughter happily agreed to let Dad do some tinkering. A few hours, an Arduino, and some Charlieplexing later, he had a nice looking clock that his kids were sure to enjoy.

If you’re interested in seeing more about how constructed, be sure to check out his YouTube channel and Instructable, where he happily provides all of the build details.

Laser tripwire security systems can be expensive propositions that don't always work as planned -- just ask Raytheon, which saw its $100 million Perimeter Intrusion Detection System for JFK International Airport undermined by one wayward jet skier. Taking that as a form of dare, Justin Huynh and teammates at Liquidware have devised a much cheaper (if also much smaller) tripwire of their own. Any interruption of a laser pointer's beam is caught by an Arduino light sensor that promptly sends the alert to an Android-running BeagleBoard xM; if a toy like Bruce the shark dares cross the line, the BeagleBoard sends a Twitter message to let the authorities, or at least Huynh, clamp down on the trespasser. The invention won't replace Raytheon's handiwork anytime soon, although Huynh notes that additional or more powerful sensors could theoretically catch real, muscle-bound sharks and not just their plastic counterparts. The supply checklist and source code are waiting on the company's project page below, so those who'd like to ward off miniature invasions can get started today.

Continue reading Liquidware team crafts laser tripwire that tweets intruder alerts, keeps fake sharks at bay (video)

Filed under: Misc. Gadgets

Liquidware team crafts laser tripwire that tweets intruder alerts, keeps fake sharks at bay (video) originally appeared on Engadget on Mon, 20 Aug 2012 19:17:00 EST. Please see our terms for use of feeds.

Hobbyist Erik Kettenburg was concerned that the size and cost of Arduino stifled his ability to craft, so he set about developing Digispark. It's an Arduino-compatible board, the size of a quarter, that offers a few pins at around a third of the cost of an Uno -- so you don't have to worry about taking projects apart when you're done. Designed to be fully compatible with the Italian standard, it's packing six I/O pins, 8k memory and a full USB connection amongst other things. The aim is to retail the gear for $12 a piece, and has been so popular that it's made nearly $100,000 in Kickstarter pledges, smashing its original goal of $5,000. We've got video for you below, and you can still throw some cash Mr. Kettenburg's way if you fancy getting your hands on one quickly.

Continue reading Digispark, Arduino's unofficial kid brother, takes Kickstarter by storm (video)

Filed under: Misc. Gadgets

Digispark, Arduino's unofficial kid brother, takes Kickstarter by storm (video) originally appeared on Engadget on Mon, 20 Aug 2012 09:39:00 EST. Please see our terms for use of feeds.

So, i've been having some trouble lately and I can't seem to find a solution on the web. I've managed to controll a brushless motor through and ESC and arduino with PWM. Nothing too dificult. What I need now is a way to controll an inversion of the motor. Like you know, changing two of the wires from the motor makes it turn the other way around.

read more

The hardware hacking village at Toorcamp provided space and tools to work on hardware. It was interesting to see what hardware hacks people had brought to work on. One example is [Owen]‘s Nibble Node.js Widget. The widget combines the popular node.js platform and custom hardware to create a node for the “internet of things.” The hardware consists of a Arduino Pro Micro, a bluetooth module, a LCD display, and a speaker in a laser cut box.

By using a custom package in node.js, the Nibble becomes an object which can be controlled by its methods. This allows for the developer to push messages to the display and control the device without worrying about the details of the hardware. Since node.js is designed for web applications, it’s simple to make the device controllable from the web.

[Owen] also wrote an emulator for the DCPU from the upcoming game, 0x10c. DCPU assembly is passed in from node.js, which compiles it and sends it to the Nibble. The device can then run the application using the DCPU emulation, which also allows for control of the display and the speaker.

There’s a lot of neat things that can be done with this minuscule cube, and [Owen] plans to release an NPM package for the node.js code.

If you're going to revisit a certain underwater dystopia, you might as well have a ball. At least that's the approach being taken by Sweden-based DIYer rasmadrak, who has decided to build a Bioshock-themed custom pinball machine just for kicks. The project is filled with lots of neat little touches from Rapture, including Little Sister vents and a few Big Daddy homages. The builder also does a pretty good job of drilling into the details and providing insight on the creation process -- like the challenge in using two different systems such as Arduino and chipKIT together, for example -- via detailed posts in the Poor Man's Pinball! blog. The project proved to be a pleasant shock to the system for fellow pinball aficionado Ben Heck, who gave the project a sprinkling of Heckendorn love via Twitter. Pinball geeks can also follow the saga, so to speak, by checking out the source link below.

Filed under: Gaming

Bioshock custom rig is Big Daddy of pinball machines, gives players a taste of Rapture originally appeared on Engadget on Sun, 19 Aug 2012 23:17:00 EST. Please see our terms for use of feeds.

Earlier this week, I showed you [Naim Busek's] kickstarter for his turn signal helmet. In that article I explained that, while the helmet is a neat idea, I was really interested in what [Naim] had told me about his power consumption.  To put it the shortest way, he has made his arduino sleep so efficiently, it can be waiting for input longer than the battery’s optimum shelf life.

After that article, [Naim] wrote in to give me the details on what he did to achieve such an efficient system. You can read his entire explanation, un altered here.

Have been searching off and on for a particular app note that I wanted to share with you but could not for the life of me find it. Seeing your post I bit the bullet and spent the last few hours searching and finally located it. The document is Designing With Logic from Texas Instruments. The interesting part is Figure 5 (will explain why a little later).

A dive into the low power operation of Arduino hardware

Started with the basics. Made sure all LED driver pins were in the off state by default. The removed the load resistors for all of the feedback LEDS I could not switch off like the one connected to VCC that wastes power any time the battery is connected. As an implementation note, I actually turned SMT resistor sideways and left them connected by one pad. Makes it easy to reinstall it if I want them later.

I had planned to not use the onboard voltage regulator from the beginning because the quiessent current it use is huge 100+ uA. The shield I designed and built used a lower current (50mA vs. 250mA) regulator since I was planning to use it only for the control electronics and sensors. The high current LEDs would run directly off of the higher voltage without any regulation. Since the micro and sensors draw 12-15mA max when fully on 50mA was way more than enough.

The expected current draw for my system was:

• Voltage regulator: ~5-6uA
• ATMega328p: ~1uA
• CMA3000 (@10Hz w/ wakeup): ~10uA

Total: ~16uA

Note: The testing below was done on both an Arduino Pro Mini and an Arduino Fio with similar results. The bike helmet prototype was built on top of an Arduino Fio.

To get the device into low power I started with the Arduino example sleep sketch and went through the guidelines from the datasheet to try and figure out why it was drawing so much power. The Arduino was using ~420uA when the chip is while the data sheet claims

Knowing that I went ahead and bypassed disconnected the supply from Arduino battery input, connected it to the input of my ultra low quiescent voltage regulator and connected the output of that directly to the Arduino VCC. Current system draw went UP to ~155uA. WTF???

Next thing I looked for was pullups on the digital lines for I2C and/or SPI. Not just pins configured as outputs and driven the wrong way but also looking at what weak pullups were intentionally (or accidentally) enabled. I have seen this catch out a number of Arduino developers. If the output value of a pin is configured high, when it is switched to being an input it does not just switch to being a high impedance input. If the digital output register is set a weak pullup (for the AVR Rpu = 20-50kOhms) is enabled on that pin. If a peripheral then decides to make that signal on that input low, the system suddenly sees an increase of VCC/Rpu of current that would not be there if the pullup were not enabled. Whenever I see a system that is some weird multiple of VCC/Rpu off of where it’s sleep current is supposed to be I will look for an input pullup that should not be enabled. In this case with a 3.3V rail a pullup would cause 60-150uA draw. Reviewed all of my code, probed the pins and did not find anything configured wrong. Happy that I didn’t screw anything up but unhappy that i Still have 140uA (of 150uA) disappearing into the ether and sucking my battery dry.

Then I started looking for some of the more obscure types of failures that could be causing this. One of those things that I discovered (then had a crash course on how to fix) is something call “back-powering of digital output pins” or sometimes “pin powering” or “port powering” of a device. Now back to Designing With Logic. Looking at Figure 5, if a chip that has digital I/O is powered down (VCC disconnected) then voltage is applied externally to that I/O that voltage can cause D1 on the input or D3 on the output to reverse bias, allow current to flow and feed the internal VCC of the chip with that voltage (minus a diode drop). Then really weird things can start happening. Most current digital chips can easily run at 1.8V (0.9V for some of the newer ones) so if a an external pin is driven at 3.3V and enough current can sneak through the diode, the part will happily keep running on the 2.7-3.0V it gets internally. Found this out the hard way with a peripheral that would never shut down and reset. Was right on the edge and drew too much current to startup by back powering but once running would happily keep running by back powering. Gave it 3.3V and it turned on took it away and it just kept on running. Was super confusing, since could turn it on but not off???

While the output of the regulator is not a digital I/O pin I got to thinking that something might still be going on with the output circuitry. So I cut the output trace from the regulator on the Fio (I just removed the regulator completely from the Pro Mini) and the current draw dropped to 34uA. This gave me a more than 10x decrease in sleep current for a 10x battery life increase. Running off of 1900mAHr AA batteries it should sleep, still doing 10Hz sampling to detect motion, for 6-7 years. With the 9V batteries in my prototype at 590mAHr it is just shy of two years.

At this point I moved forward with the kickstarter comfortable that I could hit the lifetime targets I had set. The current was still about double my back of the envelope calculations but was not going to be a showstopper. It was still weighing on me that there was something in the system that I did not know exactly how and why it was happening. Just yesterday when I was thinking about this again, I found the spark fun tutorial Adventures in Low Power Land. While I had independently done the same initial steps while going through this process I did not get to the point of looking at the brown out detection (BOD) and changing the fuses. Given that the BOD consumes 15-20uA I am now very happy with my 34uA sleep meaning that with BOD disabled I should be at 14-19uA. :) For 1900mAHr battery that gives a 10-12 year sleep time. That is well beyond the 5-7 year shelf life of a normal alkaline battery. Any time I am exceeding the storage the storage life and approaching the self depletion time of the battery I am very happy. :)

[Byrel Mitchell] wrote in to share some details on this water glider which he has been working on with his classmates at the Nonlinear Autonomous Systems lab of Michigan Technological University. As its name implies, it glides through the water rather than using propulsion systems typically found on underwater ROVs. The wings on either side of the body are fixed in place, converting changes in ballast to forward momentum.

The front of the glider is at the bottom right of the image above. Look closely and you’ll see a trio of syringes pointed toward the nose. These act as the ballast tanks. A gear motor moves a pinion connected to the syringe plungers, allowing the Arduino which drives the device to fill and empty the tanks with water. When full the nose sinks and the glider moves forward, when empty it rises to the surface which also results in forward movement.

After the break you can find two videos The first shows off the functionality and demonstrates the device in a swimming pool. The second covers the details of the control systems.

Justin Hyunh wrote in to share this cool project he and Chris Ladden built: a tweeting anti-shark laser security system! A laser pointer shines on a light sensor. An Arduino detects a low reading from the sensor and uses a BeagleBoard to send a tweet to @BruceSharkAlert and also sends a text message to Justin’s phone.

This may or may not have implications for real-life shark tracking, but I’ll take an excuse to have my shark tweet me when he (or she, I’m no marine biologist) breaches the perimeter over to the sunny side of the tank.

Of course, I’m doing this with my toy shark-on-a-stick and only a laser level and a light sensor, but it’s possible to make this much more accurate and granular just by adding more strategically placed sensors/light sources into the mix.

(In case you didn’t realize, this wasn’t meant to be a REAL shark detection system.)

I had a good discussion with Steve P. this afternoon about the order and purpose of the labs I’ve designed so far.  He’ll be putting together a list of EE topics we have to cover to coordinate with the labs, so that students will have enough theory to do each lab, but not be overwhelmed with theory that they don’t yet have a use for.

I’ve designed the labs mainly around the interests of bioengineering majors, but I’ve tried to keep in mind other possible students, such as Digital Arts and New Media students, who would be interested in practical sensor circuits for interfacing to art projects (particularly for inputs to Arduino microprocessors).

Lab 1: thermistor

See posts

1. More musings on circuits course: temperature lab
2. Temperature lab, part2
3. Temperature lab, part 3: voltage divider

The first lab will consist of 3 parts, all involving the use of a Vishay BC Components NTCLE413E2103F520L thermistor.

First, the students would use a bench multimeter to measure the resistance of the thermistor, dunking it in various water baths (with thermometers in them to measure the temperature).  They should fit a simple curve to this data (warning: temperature needs to be on an absolute scale).

Second, they would add a series resistor to make a voltage divider. They have to choose a value to get as large and linear a voltage response as possible at some specified “most-interesting” temperature (perhaps body temperature, perhaps room temperature, perhaps DNA melting temperature).  There should probably be a pre-lab exercise where they derive the formula for maximizing . They would then measure and plot the voltage output for the same set of water baths. If they do it right, they should get a much more linear response than for their resistance measurements.

Finally, they would hook up the voltage divider to an Arduino analog input and record a time series of a water bath cooling off (perhaps adding an ice cube to warm water to get a fast temperature change), and plot temperature as a function of time.

EE concepts needed: voltage, resistance, voltage divider, notion of a transducer.

Lab skills developed: use of multimeter for measuring resistance and voltage, use of Arduino with data-acquisition program to record a time series, fitting a model to data points, simple breadboarding.

Note:  Mylène suggested that we start student familiarization with the test equipment by having them use the multimeters to measure other multimeters.  What is the resistance of a multimeter that is measuring voltage?  of one that is measuring current? what current or voltage is used for the resistance measurement?  We might want to do this first.

 Lab 2: electret microphone

See posts

1. Oscilloscope practice lab
2. Op-amp lab

Mylène suggested that we start oscilloscope familiarity by looking at the output of power supplies. What ripple can you see on the voltage output of a benchtop supply? of a cheap wall wart?  This requires the students to learn the difference between DC and AC input coupling for oscilloscopes.  I think that we may be able to teach what we need here without measuring the power supplies, though that is a good backup plan.

First, we would have the students measure and plot the DC current vs. voltage for the microphone.  The microphone is normally operated with a 3V drop across it, but can stand up to 10V, so they should be able to set the Agilent E3631A power supply to various values from 0V to 10V and get the voltage and current readings directly from the bench supply, which has 4-place accuracy for both voltage and current.  There is some danger of the students accidentally delivering too much voltage and frying the mic, but as long as they get the polarity right, that isn’t too big a hazard.  Ideally, they should see that the current is nearly constant as voltage is varied—nothing like a resistor.

Second, we would have them do current-to-voltage conversion with a 5v power supply to get a 2.5v DC output and hook up the output of the microphone to the input of the oscilloscope.  Input can be whistling, talking, iPod earpiece, … . They should learn the difference between AC coupled and DC coupled inputs to the scope, and how to set the horizontal and vertical scales of the scope.

Third, we would have them design and wire their own DC blocking filter (going down to about 1Hz), and confirm that it has a similar effect to the AC coupling on the scope.

Fourth, they should play sine waves from the function generator through a loudspeaker next to the mic, observe the voltage output with the scope, and measure the voltage with a multimeter, plotting output voltage as a function of frequency.  Note: the specs for the electret mic show a fairly flat response from 50Hz to 3kHz, so most of what the students will see here is the poor response of a cheap speaker at low frequencies.  Those with extra time could look at putting the speaker and mic at opposite ends of tube and seeing what difference that makes.

EE concepts: current sources, AC vs DC, DC blocking by capacitors, RC time constant, sine waves, RMS voltage, properties varying with frequency.

Lab skills: power supply, oscilloscope, function generator, RMS AC voltage measurement.

Lab 3: electrode measurements

See posts

1. Trying to measure ionic current through small holes
2. Conductivity of saline solution
3. On stainless steel
4. Better measurement of conductivity of saline solution
5. Measuring Ag/AgCl electrodes

First, we would have the students attempt to measure the resistance of a saline solution using a pair of stainless steel electrodes and a multimeter.  This should fail, as the multimeter gradually charges the capacitance of the electrode/electrolyte interface.  For the safety of the lab equipment, we should have the beakers with salt water in a secondary containment tray at all times.

Second, the students should again use a voltage divider, with 10–100Ω load resistor, but with the function generator driving the voltage divider.  The students should measure the RMS voltage across the resistor and across the electrodes for different frequencies from 3Hz to 300kHz (the range of the AC measurements for the Agilent 34401A Multimeter).  They should plot the magnitude of the impedance of the electrodes as a function of frequency and fit an R2+(R1||C1) model to the data.  A little hand tweaking of parameters should help them understand what each parameter changes about the curve.

Third, the students should repeat the measurements and fits for different concentrations of NaCl (we’ll have to get a liter or so of each stock solution made up by one of the wet labs).  Seeing what parameters change a lot and what parameters change only slightly should help them understand the physical basis for the electrical model.

Fourth, students should make Ag/AgCl electrodes from fine silver wire. To avoid possible problems with Clorox in the lab, we’ll probably have them electroplate in NaCl solutions.  If their electrodes have an area of about 0.8 cm² (2.5cm of 18 gauge wire with a diameter of 1.024mm), we can electroplate at the recommended current density of 1mA/cm² (so 0.8mA) in 0.9% (0.16M) NaCl for a minute, reversing polarity occasionally to improve the chloride coat. The instructions I’ve seen vary a lot, so neither the salt concentration nor the current density seem to be particularly critical values. We could provide a constant-current supply, but we can probably get by with just having them use a bench supply and adjust the voltage manually to keep the current around 1mA, using visual feedback to terminate the process. (Some instructions just call for using a 9v battery and a whole coil of silver wire.)  According to Warner Instruments

The color of a well plated electrode will be light gray to a purplish gray. While plating, occasionally reversing the polarity for several seconds tends to deepen the chloride coating and yield a more stable electrode.

Fifth, the students should measure and plot the resistance of a pair of Ag/AgCl electrodes as a function of frequency (as with the stainless steel electrodes). We’ll have to think of an easy way for them to mount their electrodes so that they don’t move and so that the silver-copper interface is not near the salt water.

Sixth, if there is time, measuring the potential between a stainless steel electrode and an Ag/AgCl electrode.

EE concepts: impedance, series and parallel circuits, variation of parameters with frequency.

Electrochemistry concepts: At least a vague understanding of half-cell potentials. Ag → Ag⁺ + e^-,  Ag⁺ + Cl^- → AgCl.

Lab skills: bench power supply, function generator, multimeter, fitting functions of complex numbers, handling liquids in proximity of electronic equipment.

Lab 4: Sampling and aliasing

I don’t know the details of this lab, but Steve P. has a PC board that samples and digitizes an input with an 8-bit ADC, then reconstructs the waveform with a DAC.  He has worked out a lab for explaining and demonstrating aliasing of sampled signals using this board, a signal generator, and a dual-trace oscilloscope.  I’ll have to borrow the board and the lab handout from him to see if there is anything in the lab I’d want to tweak.

EE concepts: quantized time, quantized voltage, sampling frequency, Nyquist frequency, aliasing.

Lab skills: dual traces on oscilloscope.

Lab 5: Op amp basics

See post Op-amp lab

Use an op amp to build a simple non-inverting audio amplifier for an electret microphone, setting the gain to around 6 or 7.  Note that we are using single-power-supply op amps.

If this lab is too short, then students could feed the output of the amplifier into an analog input of the Arduino and record the waveform at the highest sampling rate they can with the software we provide (probably around 300–500 Hz).  This would again demonstrate aliasing.

EE concepts: op amp, DC bias, bias source with unity-gain amplifier, AC coupling, gain computation.

Lab skills: complicated breadboarding (enough wires to have problems with messy wiring). If we add the Arduino recording, we could get into interesting problems with buffer overrun if their sampling rate is higher than the Arduino’s USB link can handle.

Lab 6: capacitive touch sensor

See posts

1. Capacitive sensing
2. Capacitive sensing, part 2
3. Capacitive sensing with op amps
4. Capacitive sensing with op amps, continued

The students would build an op-amp oscillator (a square-wave one, not a sine wave) whose frequency is dependent on the parasitic capacitance of a touch plate, which the students can make from Al foil and plastic food wrap. Students would have to measure the frequency of the oscillator with and without the plate being touched.

We can provide a simple Arduino program that is sensitive to changes in the period of the oscillator (see example in Capacitive sensing with op amps, continued) and turns an LED on or off.

EE concepts: frequency-dependent feedback, oscillator, RC time constants, parallel capacitors.

Lab skills: more messy breadboarding.  Frequency measurement.

Lab 7: Phototransistor

See posts

1. Phototransistor
2. Synchronous demodulator
3. Pulse detection with light
4. Giving up on light-based pulse sensor
5. Looking at bioengineering measurements courses
6. Random thoughts on circuits labs

Since optical detection is such an important part of many biomolecular lab techniques, I really want to do something with an LED and phototransistor (or CdS cell or photodiode), but so far none of my ideas have worked out.  I have a nice Fairchild QRE1113 reflectance sensor that uses a matched 940nm wavelength LED and phototransistor, which I’ve used a tachometer for motors for the robotics club. Unfortunately, a tachometer is more appropriate for a mechatronics lab than a biengineering circuits course.

I thought that I might be able to use it to measure arterial pulses by reflection, but I don’t seem to get a signal at my heart rate (I did better with the uncomfortable ear clip).

The reflectance sensor is good for measuring finger tremor if you hold a finger close to (but not touching) the sensor.  The effect is optical, not capacitive coupling, since the signal is stronger if a non-conducting white piece of paper is held near the sensor rather than a finger.  The reflectance sensor is remarkably insensitive to ambient light, though shining a laser pointer on the sensor is easily detected.

We can easily do labs involving interrupting light beams, but there isn’t much “circuit” stuff for the simple ones and not much “bio” stuff either.  We could up the circuit content (perhaps too much) by modulating the light beam and using a synchronous demodulator to detect the beam even in the presence of high ambient light.

I still need to find something that is feasible and somehow related to bioengineering.  This needs more thought.

Lab 8: No idea

I’m still missing a lab.  I’ve not done anything with position, pressure, or volume sensing yet.  Of course, it is possible that some of the earlier labs will take longer than I think, and we’ll need to slip the schedule anyway.  The EKG lab looks pretty packed, so may be some portion of that could be foreshadowed here.  Perhaps bandpass filtering and characterizing a simple filter?  That would be useful, but rather boring.

Maybe an electronic music lab of some sort would be fun here?

Labs 9 and 10: EKG

See posts

1. EMG and EKG works
2. Two-stage EKG
3. EKG recording working
4. More thoughts on EKG
5. EKG blinky
6. Instrumentation amp protoboard
7. Instrumentation amp protoboard rev2.1
8. EKG blinky boards arrived

The electrocardiogram will be the final project for the course, and I think it will take two full lab sessions. The first lab session would consist of soldering up the instrumentation amp protoboard, checking for opens and shorts, and designing and characterizing a differential amplifier with an adjustable gain of about 100–1000 (including AC coupling to eliminate problems with DC offset saturating later stages).  The amplifier should have a bandwidth of about 0.01Hz–150Hz.

The second one would be and making a twisted-wire harness with alligator clips to attach to the EKG electrodes, connecting the amplifier to the electrodes, debugging the student-designed EKG amplifiers, and adjusting the gain.  I suspect that a few students will get a design that works in the first week, but that a lot of students will be doing a lot of unsoldering and resoldering as they find bugs in their design, hence the need for 2 weeks in the lab.

Student check out will require that they be able to blink an LED in time with their heart beat, display the EKG waveform on the oscilloscope, and record a minute of EKG signal at 200 samples/second using the Arduino, all without adjusting their board between demos.

EE concepts: biopotentials, instrumentation amplifier, common-mode signal, differential signal, twisted pair wiring, grounding to avoid common-mode signal saturating an instrumentation amplifier, Ac coupling, simple bandpass filtering.

Lab skills: soldering.

Summary

I have a pretty clear idea how I think the lab part of the course should start and how it should end, but there are a couple of weeks just before the end that are still a bit vague.  Perhaps as Steve starts aligning the EE topics with the labs he can identify some topics that need a lab exercise to clarify them.  Maybe some of my blog readers (those who haven’t deserted me during this long process of designing a course) can make some more suggestions—even repeating some old suggestions would not be a bad idea now, as I need a creative kick.