Non-resettable thermal fuse teardown

non-resettable-thermal-fuse

This component is a one-shot thermal fuse. When the body rises above the specified temperature the two leads stop conducting. They’re useful in applications like motors, where you want to make sure power is cut to an overheating piece of hardware before permanent damage happens. They’re pretty simple, but we still enjoyed taking a look inside thanks to [Fatkuh's] video.

The metal housing is lined with a ceramic insulator, which you can see sticking out one end in the shape of a cone. It surrounds a spring which connects to both leads and is under a bit of tension. The alloy making the connections has a low melting point — in this case it’s about 70 C — which will melt, allowing the spring to pull away and break the connection. In the clip after the break [Fatkuh] uses his soldering iron to heat the housing past the melting point, tripping the fuse. He then cracks the ceramic cone to show what’s inside.

The only problem with using a fuse like this one is you’ll need to solder in a new component if it’s ever tripped. For applications where you need a fuse that protects against over current (rather than heat) a resettable polyfuse is the way to go.

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Tracking a car like it were a computer mouse

optical-mouse-sensor-tracks-vehicle-motion

This is [Paul Mandel's] Ground-truth velocity sensor. That’s a fancy name for a device which tracks the movement of a vehicle by actually monitoring the ground its travelling over. This differs from simply measuring wheel rotation (which is how traditional odometers work) in that those systems are an indirect measurement of motion. For us the interesting part is the use of an ADNS-3080 single-chip optical mouse sensor on the left. It’s cheap, accurate, and only needs to be ruggedized before being strapped to the bottom of a car.

[Paul] designed a case that would protect the electronics and allow the sensor to mount on the uneven underbelly of a vehicle. The optical chip needs to be paired with a lens, and he went with one that cost about ten times as much as the sensor. Data is fed from the sensor to the main system controller using the PIC 18F2221. One little nugget that we learned from this project is to poll a register that always returns a default value as a sanity check. If you don’t get the expected value back it signals a communications problem, an important test for hardware going into the vibration-hell that is automotive technology.

Learn shift registers without involving a microcontroller

shift-registers-without-a-microcontroller

This is a truly hands-on approach to learning. [Kevin Darrah] ditched the microcontroller and is using push buttons to learn about 595 shift registers. The test rig uses two of the serial-in, parallel-out chips. These are cascading which means that as data from the first chip overflows it feeds the input of the second. The parts are commonly used to drive LEDs, or reduce the number of pins needed to drive peripherals like this character LCD.

The five push-buttons give you a chance to intuitively learn how the chip logic works. The blank button is also commonly called Output Enable (OE). Driving it high shuts off the outputs of the chips but doesn’t clear the data. That task is performed by the clear button which is driven low to set all of the shift register memory to zero. The other three buttons set the logic level, shift it into the chip using the clock signal, and push the stored values to the outputs using the latch.

To get a visual approximation of what’s happening inside of these chips you should check out the shift register tutorial linked to in this post.

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LTC3105 and LTC3109 energy harvesting chips

a-look-at-energy-harvester-chips

[Shahriar] devoted the lastest episode of The Signal Path to looking at energy harvesting chips. These parts are designed to gather energy from non-traditional sources as efficiently as possible. The full episode, which is embedded after the break, is about one hour long. It starts with a bit of background about the nature of these parts, and a brief overview of the wide-range of chips available. Each is suited for a different type of energy source.

He moves on to test and explain the LTC3105 and the LTC3109. The former is shown above on a development board. [Shahriar] hooks it up to his bench equipment to compare its performance to the published specs. This culminates in a circuit that uses a solar cell as the source with a super capacitor used as storage. The latter is connected to a Peltier cooler and used to convert the potential energy of ice cubes to electrical energy which charges his iPhone for about thirty seconds. This might be useful in that Peltier generator we saw last week.

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Hand soldering BGA parts should be a circus act

Okay, we think it’s questionable when people say they have no problem soldering QFN packages, but BGA? Granted this chip has far fewer balls on it than many, but it’s still quite impressive that [Xevel] was able to solder this BGA breakout by hand.

The chip you see above is a TMP006 infrared temperature sensor from TI. [Xevel] picked up the part but didn’t want to break the bank when prototyping by buying a proper PCB to host it. There are only eight conductors on it, arranged in a grid with 0.5mm pitch. That didn’t seem to scare him off, as the video after the break shows him connecting each to a conductor on a hunk of stripboard.

[Xevel] mentions that this is a dead-bug style project. Usually you glue the part upside down when using that technique, but it needs line of sight to get an accurate temperature reading so he first cut a hole in the substrate. We’d bet he’s using wire-wrapping wire to make the connections. It’s a very fine solid core wire which is perfect for this kind of work.

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Building a bipolar supply from a boost converter

This DC-DC Bipolar PSU was developed for use with a guitar effects pedal. [Obsolete Technology] needed to source both positive and negative 15V. This is pretty easy to do if you’re converting from mains, but he wanted a solution that could work with a lower-voltage AC/DC wall wort or even from batteries.

The part that pulls it all together is the LT3467. It’s a switching power regulator which offers a range of features configured by the layout of a handful of external passive components. It can put out 80 mA on each line (positive and negative). Also extremely useful for this application is the chip’s high frequency operation. Depending on the version, it switches at 1.3 or 2.1 MHz. This is high enough that it will not introduce audible noise into the audio system.

We’ve got an exercise bike whose negative supply for the LCD is blown. We’re going to try build this circuit, trimming it for our voltage needs, and get the contrast working again.

[Thanks Olli]

PCA9517 i2c translator a perfect companion for Raspberry Pi hardware add-ons

The rig pictured above works as an Internet connected temperature sensor which sends [Zaion] an email with a graph of the change over time. This in itself is interesting, but one part in particular caught our eye. He’s using an i2c temperature sensor , and we think the PCA9517 Level-Translating I2C Bus Repeater that makes it possible is a perfect match for the RPi.

This is a Texas Instruments part. You can find more about it from the company’s product page. The key words in the name of the chip are ‘Level-Translating’. This has two bus connections, each with variable voltage levels. On side A the bus can be 0.9V to 5.5V. On side B the bus range is 2.7V to 5.5V. Since the Raspberry Pi I/O pins operate at 3.3V this could connect to the B side, give you the ability to interface with i2c parts rated for lower or higher voltages. This is especially handy for folks who started with the Arduino and own mostly 5V compliant prototyping hardware.

The part comes in a SOIC package, which you can easily hand solder and will costs around $1 depending on the supplier.