Hacking has always brought more good to the world than not hacking. The successful efforts of the Allies during World War II in deciphering the Enigma machine output still reminds us of that. Today, the machine is a classic example of cryptography and bare-metal computing.

We have covered quite a few DIY Enigma machines in the past, yet 14 years old [Andy] really impressed us with his high school science fair project, a scratch built, retro-modern Enigma machine.

With its wooden enclosure, keyboard, interchangeable rotors, and plugboard, his build resembles an original Worldwar II enigma machine down to the letter. However, when looking closer, you’ll find that the rotors are implemented as electronic modules that plug into D-Sub sockets on the machine. Also, there is a 16 segment display that displays the rotor position as well as an LCD screen that lets you comfortably read the plain- and ciphertext. On the inside, you’ll find an Arduino Mega along with 1,800 other parts and 500 wires, and of course, this modern version has a backspace key.

It took [Andy] over 9 months to put all this together, and he now finds himself among the winners of the State Science & Engineering Fair (SSEF), who will be sent to Intel as representatives of their states. Given his experience in field-capable computing, we’re sure [Andy] can help Intel reconquering mobile. Enjoy the video!

Thanks to [Arduino Enigma] for the tip!

For her science fair project, [David]’s daughter had thoughts about dipping eggs in coffee, or showing how dangerous soda is to the unsuspecting tooth. Boring. Instead she employed her father to help her build a Morse Code waterfall.

[David] worked with his daughter to give her the lego bricks of knowledge needed, but she did the coding, building, and, apparently, wire-wrapping herself. Impressive!

She did the trick with two Arduinos. One controls a relay that dumps a stream of water. The other watches with an optical interrupt made from an infrared emitter and detector pair to get the message.

To send a message, type it in the keyboard. The waterfall will drop spurts of water, and then show the message on the decoder display. Pretty cool. We also liked the pulse length dial. The solution behind the LEDs is pretty clever. Video after the break.

I’ve been thinking of expanding the pressure sensor lab for the Applied Circuits Course to do something more than just measure breath pressure.  Perhaps something that conveys another physics or engineering concept.

One thing I thought of doing was measuring the back pressure and air flow on an aquarium air pump bubbling air into an aquarium. Looking at the tradeoff of flow-rate and back pressure would be a good characterization of an air pump (something I wish was clearly shown in advertisements for aquarium air pumps and air stones).  Measuring flow rate is a bit of a pain—about the best I could think of was to bubble air into an inverted soda bottle (or other known volume) and time it.

This would be a good physics experiment and might even make a decent middle-school product-science science fair project (using a cheap mechanical low-pressure gauge, rather than an electronic pressure sensor), but setting up tanks of water in an electronics lab is a logistic nightmare, and I don’t think I want to go there.

I can generate back pressure with just a simple clamp on the hose, though, and without a flow rate measurement we could do everything completely dry.

Setup for measuring the back pressure for an aquarium air pump (needs USB connection for data logger and power).

Using the Arduino data loggger my son wrote, I recorded the air pressure while adjusting the clamp (to get the y-axis scale correct, I had to use the estimated gain of the amplifier based on resistor sizes used in the amplifier).

The peak pressure, with the clamp sealing the hose shut, seems to be about 14.5 kPa (2.1psi).

I was interested in the fluctuation in the pressure, so I set the clamp to get about half the maximum back pressure, then recorded with the Arduino data logger set to its highest sampling frequency (1ms/sample).

The fluctuation in back pressure seems to have both a 60Hz and a 420Hz component with back pressure at about half maximum.

Because the Arduino data logger has trouble dealing with audio frequency signals, I decided to take another look at the signals using the Bitscope pocket analyzer.

The waveform for the pressure fluctuations from the AQT3001 air pump, with the back pressure about 7.5kPa (half the maximum).

One advantage of using the Bitscope is that it has FFT analysis:

Spectrum for the back pressure fluctuation. One can see many of the multiples of 60Hz, with the particularly strong peak at 420Hz.

I was also interested in testing a Whisper40 air pump (a more powerful, but quieter, pump). When I clamped the hose shut for that air pump, the hi-gain output of the amplifier for the pressure sensor saturated, so I had to use the low gain output to determine the maximum pressure (24.8kPA, or about 3.6psi). The cheap Grafco clamp that I used is a bit hard to get complete shutoff with (I needed to adjust the position of the tubing and use pliers to turn the knob).  It is easy to get complete shutoff if the tube is folded over, but then modulation of less than complete shutoff is difficult.

The fluctuation in pressure shows a different waveform from the AQT3001:

The Whisper40 air pump, with the clamp set to get a bit less than half the maximum back pressure, produces a 60Hz sawtooth pressure waveform, without the strong 420Hz component seen from the AQT3001. The peak-to-peak fluctuation in pressure seems to be largest around this back pressure. The 3kPa fluctuation is larger than for the AQT3001, but the pump seems quieter.

The main noise from the pump is not from the fluctuation in the pressure in the air hose, but radiation from the case of the pump. That noise seems to be least when the back pressure is about 1.1kPa (not at zero, surprisingly). The fluctuation is then all positive pressure, ranging from 0 to 2.2kPa and is nearly sinusoidal, with some 2nd and 3rd harmonic.

As the back pressure increases for the Whisper40, the 2nd, 3rd, and 4th harmonics get larger, but the 60Hz fundamental gets smaller. The 4th harmonic is maximized (with the 1st through 4th harmonics almost equal) at about 22.8kPa, above which all harmonics get smaller, until the air hose is completely pinched off and there is no pressure variation.

When driving the large airstone in our aquarium, the Whisper40 has a back pressure of about 7.50kPa (1.1psi) with a peak-to-peak fluctuation of about 2.6kPa.

I’m not sure whether this air-pump back-pressure experiment is worth adding to the pressure sensor lab.  If I decide to do it, we would need to get a dozen cheap air pumps.  The Tetra 77853 Whisper 40 air pump is $11.83 each from Amazon, but the smaller one for 10-gallon aquariums is only $6.88.  With 12 Ts and 12 clamps, this would cost about $108, which is not a significant cost for the lab.

I’ve been thinking of expanding the pressure sensor lab for the Applied Circuits Course to do something more than just measure breath pressure.  Perhaps something that conveys another physics or engineering concept.

One thing I thought of doing was measuring the back pressure and air flow on an aquarium air pump bubbling air into an aquarium. Looking at the tradeoff of flow-rate and back pressure would be a good characterization of an air pump (something I wish was clearly shown in advertisements for aquarium air pumps and air stones).  Measuring flow rate is a bit of a pain—about the best I could think of was to bubble air into an inverted soda bottle (or other known volume) and time it.

This would be a good physics experiment and might even make a decent middle-school product-science science fair project (using a cheap mechanical low-pressure gauge, rather than an electronic pressure sensor), but setting up tanks of water in an electronics lab is a logistic nightmare, and I don’t think I want to go there.

I can generate back pressure with just a simple clamp on the hose, though, and without a flow rate measurement we could do everything completely dry.

Setup for measuring the back pressure for an aquarium air pump (needs USB connection for data logger and power).

Using the Arduino data loggger my son wrote, I recorded the air pressure while adjusting the clamp (to get the y-axis scale correct, I had to use the estimated gain of the amplifier based on resistor sizes used in the amplifier).

The peak pressure, with the clamp sealing the hose shut, seems to be about 14.5 kPa (2.1psi).

I was interested in the fluctuation in the pressure, so I set the clamp to get about half the maximum back pressure, then recorded with the Arduino data logger set to its highest sampling frequency (1ms/sample).

The fluctuation in back pressure seems to have both a 60Hz and a 420Hz component with back pressure at about half maximum.

Because the Arduino data logger has trouble dealing with audio frequency signals, I decided to take another look at the signals using the Bitscope pocket analyzer.

The waveform for the pressure fluctuations from the AQT3001 air pump, with the back pressure about 7.5kPa (half the maximum).

One advantage of using the Bitscope is that it has FFT analysis:

Spectrum for the back pressure fluctuation. One can see many of the multiples of 60Hz, with the particularly strong peak at 420Hz.

I was also interested in testing a Whisper40 air pump (a more powerful, but quieter, pump). When I clamped the hose shut for that air pump, the hi-gain output of the amplifier for the pressure sensor saturated, so I had to use the low gain output to determine the maximum pressure (24.8kPA, or about 3.6psi). The cheap Grafco clamp that I used is a bit hard to get complete shutoff with (I needed to adjust the position of the tubing and use pliers to turn the knob).  It is easy to get complete shutoff if the tube is folded over, but then modulation of less than complete shutoff is difficult.

The fluctuation in pressure shows a different waveform from the AQT3001:

The Whisper40 air pump, with the clamp set to get a bit less than half the maximum back pressure, produces a 60Hz sawtooth pressure waveform, without the strong 420Hz component seen from the AQT3001. The peak-to-peak fluctuation in pressure seems to be largest around this back pressure. The 3kPa fluctuation is larger than for the AQT3001, but the pump seems quieter.

The main noise from the pump is not from the fluctuation in the pressure in the air hose, but radiation from the case of the pump. That noise seems to be least when the back pressure is about 1.1kPa (not at zero, surprisingly). The fluctuation is then all positive pressure, ranging from 0 to 2.2kPa and is nearly sinusoidal, with some 2nd and 3rd harmonic.

As the back pressure increases for the Whisper40, the 2nd, 3rd, and 4th harmonics get larger, but the 60Hz fundamental gets smaller. The 4th harmonic is maximized (with the 1st through 4th harmonics almost equal) at about 22.8kPa, above which all harmonics get smaller, until the air hose is completely pinched off and there is no pressure variation.

When driving the large airstone in our aquarium, the Whisper40 has a back pressure of about 7.50kPa (1.1psi) with a peak-to-peak fluctuation of about 2.6kPa.

I’m not sure whether this air-pump back-pressure experiment is worth adding to the pressure sensor lab.  If I decide to do it, we would need to get a dozen cheap air pumps.  The Tetra 77853 Whisper 40 air pump is $11.83 each from Amazon, but the smaller one for 10-gallon aquariums is only $6.88.  With 12 Ts and 12 clamps, this would cost about $108, which is not a significant cost for the lab.

Over winter break, my son has been working nearly full time on writing data logging software for my students to use in the Applied Circuits for Bioengineers course. He has made the first public beta release (v1.0.0b1) today on BitBucket. (Note: you may have to click on the “tags” tab to get to the view that shows the v1.0.0b1 link. The BitBucket link directly to that view seems to be broken—that’s open issue 5504 in BitBucket’s own issue tracker.)

We’ve only tested the code on Mac OS X computers with Arduino Duemilanove and Uno boards, though we’ve tested a slightly earlier version on Windows.  The code should also run on Linux and with Leonardo and Mega boards, but has not been tested on these platforms. We welcome users testing the code for us—report any problems using the BitBucket issue tracker for the project.  The documentation is still in a fairly primitive state—report issues with that also, so that they can be fixed.

The overall goal is fairly simple: to have an easy-to-use way to record timestamps, voltages, and digital values from the Arduino into files on a host computer, without needing auxiliary hardware (like the Adafruit data logger shield that I bought for myself and assembled yesterday).

The user can specify what analog and digital pins to record and when to record the values.  When to record can be specified either   as interrupts on pins or as fixed timing intervals:

View of the two windows of the user interface.

The “volts measured” for the reference is stored as metadata in the output file and can be used for scaling the Arduino numbers (if “Convert to Volts” is checked).  The scaling can be an arbitrary value for the full-scale reading or can be the voltage measured with an external multimeter at the AREF pin.

This software has been through several versions:

1. The first version of the code was one I wrote last spring that just recorded interrupt times in an Arduino array and dumped them out over the USB cable after it was done (see Homemade super pulley).
2. My son was not happy with that crude program of mine and rewrote it in June to have use the Arduino memory as a queue and send the time stamps to a Python program on the laptop (see Improved super pulley code).  That program introduced him to three new concepts: circular buffers for queues, interrupts, and multi-threading, all of which he researched for himself. That version of the code mainly used a command line interface, but he used the curses package for a crude user interface.
3. He added a PyGUI graphical user interface, but that slowed down the code on the laptop and eventually grew to be difficult to maintain.
4. He decided to try to make the software by portable between three platforms (Mac OS X, Windows, and Linux) despite their very different ways of dealing with the USB serial ports, to run under both Python2.7 and Python3, and to require only minimal non-standard packages (mainly PySerial and the Arduino package Timer1).  He refactored the code completely and built the GUI using Tkinter. This has lead to the current version of the code, which is finally working robustly enough to let the bioengineering students use it.

It has been a good software-engineering experience for my son, and he has learned a lot.  In the process of developing this code, he has learned a lot about interrupts, using queues to communicate between processors and between threads, platform-independence, a couple of different GUI libraries, the value of version control and bug-tracking, race conditions, interface design for non-expert users, and even some things about documentation.

I’ve been acting mainly as a customer for this code, entering bug reports and suggesting new features, though I have occasionally helped him debug.  For example, we just spent fifteen minutes reading Section 15 “16-bit Timer/Counter1 with PWM” of the ATMega328 data sheet, trying to figure out why the first time interval was wrong.  It turns out that timer interrupt is raised immediately when the interrupt is enabled, unless the timer-overflow flag is turned off first.

My son may use this project as a science fair entry this year, though it was not started with that idea, and we discussed that possibility for the first time today.  The big problem is that this is purely an engineering project, not a “science” project, and trying to fake a hypothesis is not something we’ll consider.

Over winter break, my son has been working nearly full time on writing data logging software for my students to use in the Applied Circuits for Bioengineers course. He has made the first public beta release (v1.0.0b1) today on BitBucket. (Note: you may have to click on the “tags” tab to get to the view that shows the v1.0.0b1 link. The BitBucket link directly to that view seems to be broken—that’s open issue 5504 in BitBucket’s own issue tracker.)

We’ve only tested the code on Mac OS X computers with Arduino Duemilanove and Uno boards, though we’ve tested a slightly earlier version on Windows.  The code should also run on Linux and with Leonardo and Mega boards, but has not been tested on these platforms. We welcome users testing the code for us—report any problems using the BitBucket issue tracker for the project.  The documentation is still in a fairly primitive state—report issues with that also, so that they can be fixed.

The overall goal is fairly simple: to have an easy-to-use way to record timestamps, voltages, and digital values from the Arduino into files on a host computer, without needing auxiliary hardware (like the Adafruit data logger shield that I bought for myself and assembled yesterday).

The user can specify what analog and digital pins to record and when to record the values.  When to record can be specified either   as interrupts on pins or as fixed timing intervals:

View of the two windows of the user interface.

The “volts measured” for the reference is stored as metadata in the output file and can be used for scaling the Arduino numbers (if “Convert to Volts” is checked).  The scaling can be an arbitrary value for the full-scale reading or can be the voltage measured with an external multimeter at the AREF pin.

This software has been through several versions:

1. The first version of the code was one I wrote last spring that just recorded interrupt times in an Arduino array and dumped them out over the USB cable after it was done (see Homemade super pulley).
2. My son was not happy with that crude program of mine and rewrote it in June to have use the Arduino memory as a queue and send the time stamps to a Python program on the laptop (see Improved super pulley code).  That program introduced him to three new concepts: circular buffers for queues, interrupts, and multi-threading, all of which he researched for himself. That version of the code mainly used a command line interface, but he used the curses package for a crude user interface.
3. He added a PyGUI graphical user interface, but that slowed down the code on the laptop and eventually grew to be difficult to maintain.
4. He decided to try to make the software by portable between three platforms (Mac OS X, Windows, and Linux) despite their very different ways of dealing with the USB serial ports, to run under both Python2.7 and Python3, and to require only minimal non-standard packages (mainly PySerial and the Arduino package Timer1).  He refactored the code completely and built the GUI using Tkinter. This has lead to the current version of the code, which is finally working robustly enough to let the bioengineering students use it.

It has been a good software-engineering experience for my son, and he has learned a lot.  In the process of developing this code, he has learned a lot about interrupts, using queues to communicate between processors and between threads, platform-independence, a couple of different GUI libraries, the value of version control and bug-tracking, race conditions, interface design for non-expert users, and even some things about documentation.

I’ve been acting mainly as a customer for this code, entering bug reports and suggesting new features, though I have occasionally helped him debug.  For example, we just spent fifteen minutes reading Section 15 “16-bit Timer/Counter1 with PWM” of the ATMega328 data sheet, trying to figure out why the first time interval was wrong.  It turns out that timer interrupt is raised immediately when the interrupt is enabled, unless the timer-overflow flag is turned off first.

My son may use this project as a science fair entry this year, though it was not started with that idea, and we discussed that possibility for the first time today.  The big problem is that this is purely an engineering project, not a “science” project, and trying to fake a hypothesis is not something we’ll consider.