Touch sensors: overview, theory, and construction

This collection of touch sensor information should be of interest to anyone who liked the simple touch sensor post from Thursday. That was a resistive touch sensor and is covered in detail along with AC hum sensors that trigger based on induced current from power lines around you, and capacitive touch switches like we’ve seen in past hacks. Each different concept is discussed and clearly illustrated like the slide above. [Giorgos Lazaridis] has also put together individual posts that build and demonstrate the circuits. We’ve embedded his resistive sensor demo video after the break and linked to all three example circuits.

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Power supplies and transformers; a learning experience

[Ladyada] is working on a tutorial series covering power supplies. If you’ve ever built an electronic project you’ve used some type of power supply but we think that most people have no idea how you get from mains power to the DC voltages that most small projects use. So if you want to learn, get started with the first installment which covers AC/DC converters based on a transformer like the one seen above.

These transformers are inside the heavy and hot wall-wart plugs that come with many electronics. We used one along with a breadboard power supply when building the pumpkin LED matrix. They use a pair of coils to step down the voltage to a much smaller level. From there it’s a matter of rectifying the AC into DC power, which she talks about in an easy to follow discussion.

We understand this type of converter quite well but we’re a bit foggy on switch-mode AC/DC converters that don’t use a transformer. They’re much better because you don’t have to build a regulator into the target project like you do with wall-warts. Can’t wait until she gets to that part of the series!

EL Wire: make it, connect it, power it

[Jeri’s] back with a series of videos that outlines the step-by-step electroluminescent wire manufacturing, making EL panels from PCBs, and assembling power supplies for EL hardware. These concepts are actually quite approachable, something we don’t expect from someone who makes their own integrated circuits at home.

The concept here is that an alternating current traveling through phosphors will excite them and produce light. You need two conductors separated by a dielectric to get the job done. For wire, [Jeri] uses one strand of enameled magnet wire and one strand of bare wire. The enamel insulates them, protecting against a short circuit.

But that’s not all, she also tests using a circuit board as an EL panel. By repurposing the ground plane as one of the conductors, and using the solder mask as the dielectric she is able to paint on a phosphor product resulting in the glowing panel.

Finally, you’ve got to get juice to the circuit and that’s where her power supply video comes into the picture. We’ve embedded all three after the break. It’s possible that this is cooler than blinking LEDs and it’s fairly inexpensive to get started. The circuitry is forgiving, as long as you don’t zap yourself with that alternating current.

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Super simple Arduino setup lowers electricity bills

An Arduino with 40 lines of code, a temperature resistor, and servo are all that’s truly needed to save some dough with this thermostat by [Peter Hamilton]. LEDs and a potentiometer are added as well to help set and read the desired temperature. With or without said additional parts, the hack is still ridiculously simple and we’re wondering why we didn’t have a similar setup on our blisteringly cold office AC system before seeing it.

Though, we’re going a bit further with our version, plans are in the making to add timers to turn off the system for extended hours while no one is at the office. What would you add?

Neon binary clock

[Josiah] said ‘no’ to LEDs and instead used blue-phosphor neon lamps to build this binary clock. The ATmega328 inside uses three 8-bit shift registers to control the display. Each lamp needs a high-voltage NPN transistor in order to switch on the 150V necessary for proper illumination. A simple circuit was used to pull a 60 Hz clock signal out of the incoming 16VAC power. Unfortunately it was a bit too simple and didn’t provide a clean signal. [Josiah’s] workaround is something of a debounce subroutine in the firmware to prevent multiple interrupts on the falling edge.

The last project we saw from [Josiah] was the Coachella Lamp. That was a show piece of antiquated technology and this is another show piece with a minimalistic style. We also liked seeing the protoboard work on the inside. That’s a pretty jam-packed circuit board and keeping everything in the right place while you build up each trace with blobs of solder is no small feat.

SPRIME controlled AC outlets

Reader [Tim Upthegrove] sent in a novel take on powering and monitoring AC outlets and devices called SPRIME, or Simple Powerline Remote Interactive Monitor and Enforcer. Compared to previous hacks, such as 120v switching or Quick cheap remote outlets, that only turned an outlet on or off; SPRIME allows not only control over outlets via the internet, but also power usage of devices currently plugged in.

We really liked their idea of giving power companies access to SPRIME outlets to reduce power consumption during peak hours, but sadly we don’t see it being implemented in homes any time soon. Catch a video of SPRIME after the rift.

[Thanks Chris McClanahan and Jeff Starker for the project, and deyjavont for pointing out our silly mistakes]

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Logic clock without an on-board oscillator

[Lucassiglo21] developed this logic clock without using a crystal oscillator or a resonator. Instead, he’s letting the incoming electricity keep the time for him. The supply is AC at 50 Hz so he’s using some 4017 decade dividers to reduce that down to a 1 Hz signal. From there it keeps track of the ticks just like the last digital logic clock we saw.

If you’ve used AC line frequency as the clock source in your project we’d like to hear about it. Send us a tip and make sure your writeup includes a schematic. We’re especially interested to see if anyone has a good way of using this method with inexpensive microcontrollers.