Passive, but not Innocuous

Maxim Integrated recently posted a series of application notes chronicling how there’s more going on than you’d think in even the simplest “passive” components. Nothing’s safe: capacitors, resistors, and even printed circuit boards can all behave in non-ideal ways, and that can bite you in the reflow-oven if you’re not aware of them.

You might already know that capacitors have an equivalent series resistance that limits how fast they can discharge, and an equivalent inductance that models departures from ideal behavior at higher frequencies. But did you know that ceramic capacitors can also act like voltage sources, acting piezoelectrically under physical stress?

For resistors, you’ll also have to reckon with temperature dependence as well as the same range of piezoelectric and inductance characteristics that capacitors display. Worse, resistors can display variable resistance under higher voltages, and actually produce a small amount of random noise: Johnson Noise that depends on the value of the resistance.

Finally, the third article in the series tackles the PCB, summarizing a lot of potential manufacturing defects to look out for, as well as covering the parasitic capacitance, leakage currents, and frequency dependence that the actual fiberglass layers themselves can introduce into your circuit.

If you’re having a feeling of déjà-vu, the same series of articles ran in 2013 in Electronic Design but they’re good enough that we hope you won’t mind the redundant repetition all over again. And if you’re already quibbling with exactly what they mean by “passive”, we feel your pain: they’re really talking about parasitic effects, but we’ll let that slide too. We’re in a giving mood today.

[via Dangerous Prototypes]

Gathering the Hacking Community of Zurich

When my Swiss cousin-in-law sent us her wedding invitation, I didn’t immediately think I’d get to see user [antti.lukats‘] tiny FPGA projects as part of the deal. I’m really glad that I came to Switzerland for the wedding, and also got to be a part of an awesome meetup in Zurich’s Fablab. [Antti], who was at the meetup, is pictured above holding a small tube full of FPGAs, he’s a Hackaday Prize Best Product finalist with FPGA project DIPSY.

As is becoming the norm for Hackaday meetups, we ask people to bring projects. We then count all the people who want to present something and squeeze all the presentations into just about 90 minutes. Before and after the lightening talks, there’s always plenty of time to walk around and see individual projects, meet people and of course eat and drink.

There were 3 walking robots and 2 rolling robots presented. [Arian’s] Roomba had the popular ESP8266 hacked into it. [Simon] brought a RaspberryPi powered rolling robot. [Thomas] brought a walking robot which walked quite well. The last walking robot of the night was shown just on video. [Radomir Dopieralski] brought his Hackaday Prize entry, the very cool and easy to use Tote robot. The Tote aims to fix the problem the world has without enough walking robots by creating an easy platform to build walking robots upon. It seemed at this meetup, that [Radomir’s] dream of many walking robots had been found.

[Oscarv] brought the insanely cool PiDP. The PiDP-8/I is another Hackaday Prize Best Product finalist, it’s a replica of the first minicomputer. [Oscar’s] version uses a Raspberry Pi to recreate all the operations. [Neil’s] SoftVGA is a software only VGA generator. I expect to see many more cool projects like these two next week at the Vintage Computing Festival in Berlin. I’ll be there with [Elliot] and [Bilke] and we’re having a Meetup with the VCF folks Oct 3rd.

[tamberg] presented a beautifully fabricated clear cube with switches on the inside, a metal ball rolls around and activates the switches. The Larson scanner next to it was designed by [stefan-xp]. [Yvonne] discussed her recent light painting “Topology of Light” and [Isaac] was sick of playing 4 in a row alone, so he built a robot to play the game with!

A popular hacker project is automatic watering of indoor or outdoor gardens. [Effi] nailed it with a brilliant presentation about moisture sensors while showing us how well her plants are doing.

There were far too many projects to list everything here, but [Thibault‘s] Bit Shift project really caught my eye. This project has several panels daisy chained together with layers of blue thermochromatic pigment on top of white primer.Each panel is a PCB, a heat pad controlled in a timed heating sequence powered by ATtinys. After each panel heats up, there is a 20 second delay before the next panel heats up. When the blue thermochromatic pigment reaches 37°c it turns transparent, and the white undercoating shows through. As the square cools down, the transparent pigment turns blue again. You can catch the video here.

Screen Shot 2015-09-28 at 11.32.43 PM

I hope to see some of you in Berlin, and if you missed it, we just put out the call for proposals for Hackaday’s first hardware conference.

The 2015 Hackaday Prize is sponsored by:

9th Grader Arrested, Searched for Building a Clock

A 14-year-old in Dallas, Texas has been arrested for bringing a clock to his school. [Ahmed Mohamed] could be any one of us. He’s a tinkerer, pulling apart scrap appliances and building projects from the parts. He was a member of the his middle school robotics team. The clock was built from a standard four digit seven segment display and a circuit board. [Ahmed] built the circuit inside a Vaultz hard pencil case like this one. He then did what every other experimenter, inventor, hacker, or maker before him has done: He showed off his creation.

Unfortunately for [Ahmed] one of his teachers immediately leapt to the conclusion that this electronic project was a “hoax bomb” of some sort. The police were called, [Ahmed] was pulled out of class and arrested. He was then brought to a detention center where he and his possessions were searched. [Ahmed] is now serving a three-day suspension from school. His clock is considered evidence to be used in a possible criminal case against him.

If this situation doesn’t get your blood boiling, then we don’t know what does. Not only is there a glaring racial issue here, but also an issue of allowing kids to bring their projects to school. We hope you’ll join us in expressing outrage at this whole debacle, as well as supporting [Ahmed] in any way you can. Let’s join together as a community to make sure a few small-minded individuals don’t break the spirit of this budding hardware hacker.

For anyone out there who would like to support [Ahmed]’s education even when his school won’t, [Anil Dash] is will be in contact with the family later today. We’re offering a gift card for the hackaday store and we would assume other contributions would also be welcome. -Ed.

Continue reading “9th Grader Arrested, Searched for Building a Clock”

Demonstrating Science at Harvard University

What if there was a job where you built, serviced, and prepared science demonstrations? This means showing off everything from principles of physics, to electronic theory, to chemistry and biology. Would you grab onto that job with both hands and never let go? That was my reaction when I met [Dan Rosenberg] who is a Science Lecture Demonstrator at Harvard University. He gave me a tour of the Science Center, as well as a behind the scenes look at some of the apparatus he works with and has built.

Continue reading “Demonstrating Science at Harvard University”

Upgrading an Old Camera with a New Light Meter

[Marc] has an old Voigtländer Vito CLR film camera. The camera originally came with an analog light meter built-in. The meter consisted of a type of solar panel hooked up to a coil and a needle. As more light reached the solar panel, the coil became energized more and more, which moved the needle farther and farther. It was a simple way of doing things, but it has a down side. The photo panels stop working over time. That’s why [Marc] decided to build a custom light meter using newer technology.

[Marc] had to work within the confines of the tiny space inside of the camera. He chose to use a LM3914 bar display driver IC as the primary component. This chip can sense an input voltage against a reference voltage and then display the result by illuminating a single LED from a row of ten LEDs.

[Marc] used a photo cell from an old calculator to detect the ambient light. This acts as a current source, but he needed a voltage source. He designed a transimpedence amplifier into his circuit to convert the current into a voltage. The circuit is powered with two 3V coil cell batteries, regulated to 5V. The 5V acts as his reference voltage for the display driver. With that in mind, [Marc] had to amplify this signal further.

It didn’t end there, though. [Marc] discovered that when sampling natural light, the system worked as intended. When he sampled light from incandescent light bulbs, he did not get the expected output. This turned out to be caused by the fact that incandescent lights flicker at a rate of 50/60 Hz. His sensor was picking this up and the sinusoidal output was causing problems in his circuit. He remedied this by adding two filtering capacitors.

The whole circuit fits on a tiny PCB that slides right into position where the original light meter used to be. It’s impressive how perfectly it fits considering everything that is happening in this circuit.

[Thanks Mojay]

Vibrating Distance Torch Illuminates the Dark without Light

If you’ve ever had to move around in a dark room before, you know how frustrating it can be. This is especially true if you are in an unfamiliar place. [Brian] has attempted to help solve this problem by building a vibrating distance sensor that is intuitive to use.

The main circuit is rather simple. An Arduino is hooked up to both an ultrasonic distance sensor and a vibrating motor. The distance sensor uses sound to determine the distance of an object by calculating how long it takes for an emitted sound to return to the sensor. The sensor uses sounds that are above the range of human hearing, so no one in the vicinity will hear it. The Arduino then vibrates a motor quickly if the object is very close, or slowly if it is far away. The whole circuit is powered by a 9V battery.

The real trick to this project is that the entire thing is housed inside of an old flashlight. [Brian] used OpenSCAD to design a custom plastic mount. This mount replaces the flashlight lens and allows the ultrasonic sensor to be secured to the front of the flashlight. The flashlight housing makes the device very intuitive to use. You simply point the flashlight in front of you and press the button. Instead of shining a bright light, the flashlight vibrates to let you know if the way ahead is clear. This way the user can more easily navigate around in the dark without the risk of being seen or waking up people in the area.

This reminds us of project Tacit, which used two of these ultrasonic sensors mounted on a fingerless glove.

A Simple Circuit For Testing Infrared Remote Controls

Every now and then a remote control acts up. Maybe you are trying to change the channel on your television and it’s just not working. A quick way to determine if the remote control is still working is by using a cell phone camera to try to see if the IR LED is still lighting up. That can work sometimes but not always. [Rui] had this problem and he decided to build his own circuit to make it easier to tell if a remote control was having problems.

The circuit uses a Vishay V34836 infrared receiver to pick up the invisible signals that are sent from a remote control. A Microchip 12F683 processes the data and has two main output modes. If the remote control is receiving data continuously, then a green LED lights up to indicate that the remote is functioning properly. If some data is received but not in a continuous stream, then a yellow LED lights up instead. This indicates that the batteries on the remote need to be replaced.

The circuit also includes a red LED as a power indicator as well as RS232 output of the actual received data. The PCB was cut using a milling machine. It’s glued to the top of a dual AAA battery holder, which provides plenty of current to run the circuit.