Vintage Microammeter Now Tells Temperature

[Craig] sent in this tip about a simple hack he built to convert an old analog micro-ammeter into a thermometer using a few parts. There’s a certain charm to retro analog meters, and there was enough space inside the old meter to accommodate the tiny breadboarded circuit and the three AA batteries to convert it into a cool looking centerpiece which is useful too!

He used the 3-pin MCP9700 analog temperature sensor connected to a LTC1541 – a combined comparator, op-amp and band gap reference voltage all rolled into one package. The thermometer displays 1uA per degree Celsius, has an output of 1mV per degree Celsius for external temperature monitoring / data logging, and draws just about 20uA. While the build itself is pretty simple, [Craig] took the time to walk through every design decision he made in the video after the break. This starts with the design for his circuit, and  moves on to the selection of parts and their values. The video is a must-watch for anyone wanting to learn more about precision op-amp based designs.

The three batteries will drain over time, and a circuit like this one requires a stable reference voltage. That is taken care by the bandgap reference voltage from the LTC1541. This eliminates the use of additional voltage regulators, and allows the circuit to work from 4.5V down to about 3.3V. Check the video after the break to listen to [Craig] describe how it works. We’re not sure how quickly it responds to changes in ambient temperature since the sensor is enclosed inside the meter, so maybe some vents at the back, or bringing out the sensor might be a good idea.

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Smarter-than-wood Saw Blade Makes Perfect Foldable Joints

[Andrew Klein] knows the pain of building drawers from plywood. It can be a pain to get all of the pieces measured and cut just right. Then you have to line them up, glue them together, and clamp them perfectly. It’s time-consuming and frustrating. Then one day it hit him that he might be able to make the whole process much easier using a custom saw blade.

The the video below, [Andrew] does a great job explaining how the concept works using a piece of paper. The trick is that the plywood must be cut in a very specific shape. This shape results in the plywood just barely being held together, almost as if it’s hinged. The resulting groove can then be filled with wood glue, and the plywood is folded over on itself. This folding process leaves no gaps in the wood and results in a strong joint. Luckily this special shape can be cut with a specialized saw blade.

This new process removes the requirement of having five separate pieces for a drawer. Instead, only four cuts are needed on a single piece of square plywood. The corners are then removed with a razor blade and all four sides are folded up and into place. [Andrew] shows that his prototype blade needs a little bit of work, but he’s so hopeful that this new invention will be useful to others. Continue reading “Smarter-than-wood Saw Blade Makes Perfect Foldable Joints”

Move Over Red Bull, Hot Wire Foam Cutter Now Gives You Wings

Not many people will argue with flying RC airplanes is super fun. One big bummer is when a crash damages a part beyond repair. Sure, the RC pilot could keep buying replacement parts but doing so will add up after a while. RC plane builder and general guy with a cool name, [HuckinChikn], decided to build a hot wire foam cutter so making replacement wings would be quick and cheap.

The actual hot wire part is nothing special, just some wire pulled taut across a frame and a 24 vdc power supply pumping out current and heating the wire so it melts any foam in its path. The unique part of the build is that one side of the hot wire frame is secured in place and only allowed to pivot about that point. The other side of the frame traces an airfoil-shaped pattern. This setup allows [HuckinChikn] to make tapered wings. The difference between a straight wing and a tapered wing is similar to that of a cylinder and cone.

hotwire foam wing cutter

Check out the video after the break for a quick demonstration how easy it is to make a wing when you have the right tool!

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Hacking Amazing Soldering Features into the Already Great Weller WMRP

Weller, the German soldering tools manufacturer, has a nice range of micro soldering irons (pencils) designated as the WMRP series. These are 12V, 40 W or 55W units with a 3 second heat up time, and allow quick tip exchange without needing any tools. [FlyGlas] built a neat soldering station / controller for the WMRP series based around an ATMega microcontroller running Arduino.

It’s packed with most of the features you see in a professional rig.

  • low offset op amp for soldering tip temperature measurement with type c thermocouple
  • cold junction compensation using the PTC (KTY82-210) included in the WMRP soldering pencil
  • input voltage measurement
  • soldering pencil current measurement
  • recognizing if the soldering pencil rests in the stand (–> standby)
  • 3 buttons to save and recall temperature values
  • rotary encoder to set soldering temperature
  • illuminated 16×2 character LCD module
  • USB for debugging and firmware update
  • 4mm safety socket for +12V power input and a protective earth socket for connection to ESD protection

WMRP_controller_02A PWM signal from the microcontroller controls the load current using a MOSFET. Load current is measured using a Hall Effect-Based Linear Current Sensor – ACS712. The corresponding linear output voltage is buffered and slightly amplified using AD8552 zero drift, single supply, RRIO Dual Op Amp before being sent to the microcontroller ADC input. To ensure ADC measurements are accurate and stable, a low noise precision voltage reference – ADR392 is used. Another precision resistive voltage divider allows input voltage measurement. The supply input has over-current and reverse voltage protection. A set of buttons and a rotary encoder are connected to the microcontroller to allow settings and adjustments. An analog section measures the thermocouple voltage from the soldering pencil as well as the stand-by switch status. The handle has an embedded reed switch that is activated by a magnet in the support stand which puts it into stand-by mode. Another analog section performs cold junction compensation using the PTC sensor within the soldering pencil.

The Git repo contains the initial Arduino code which is still a work in progress. While the hardware source files are not available, the repo does have the pdf’s, gerbers and BOM list, if you want to take a shot at building it. Check a demo video after the break. Thanks [Martin] for sending in the tip.

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DIY Concrete Mixing Wheelbarrow Made from Recycled Parts

[Dan] had a bunch of concrete mixing to do. Sure, it was possible to stand there and mix concrete and water in a wheelbarrow for hours and hours but that sounds like a tedious task. Instead, [Dan] looked around the shop to see if he had parts available to make a concrete mixer. As you may have guessed, he did. Instead of stopping at just a concrete mixer, he decided to make a concrete mixing wheelbarrow!

The frame is built out of plywood left over from a past canoe project. The frame holds a mixing barrel that was also hanging around the shop. From the photo, the drive system looks simple but it is not. First, the small motor pulley spins a larger pulley that is in-line with the barrel. Gearing down the drive this way increases torque available to spin the barrel, and that gear reduction is necessary to spin the heavy concrete slowly. What you can’t see is a planetary gear system that gears down the drive train again. The gears are cut out of plywood and were designed in this Gear Generator program. The sun (center) gear of the planetary setup is supported by another scavenged part, a wheel bearing from a Chevy minivan.

Now [Dan] can mix all the concrete he wants, wheel it over and dump it wherever he needs it. With the exception of the drive belt and some miscellaneous hardware, all the parts were recycled.

New Cross Bladed Axe Not For Cosplay or Larping

Firewood aficionado and general axing enthusiast [KH4] likes to cut and split his own fire wood. To burn a tree trunk sized piece of wood efficiently, it has to be split into 4 smaller pieces. [KH4] does this with 3 axe swings, the first splitting the main log in 2, then splitting each half in half again. Although he likes swinging the mighty axe, he still would like to increase the efficiency of each swing.

Well he’s done it! This is accomplished by making a Cross Bladed Axe that has an X-shaped head. Each axe swing should split a log into 4 pieces. That results in 66% less swings for the same amount of wood split!

This projected started with two spare axe heads. One was cut in half with an angle grinder. The two axe head halves were then ground down so that they match the contour of the original axe head. Once the fit was good, the welder was broken out and all 3 axe head pieces were combined into one beastly mass.

After the new head was polished and sharpened, it was re-assembled a new hickory handle. We have to say, the end product looks pretty awesome. There’s a video after the break of this axe in action. Check it out!

Have you ever seen how these axe heads used to be manufactured?

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Printed Tentacles for PCB Probing

Every hacker workbench has one or more of those “helping hand” devices to aid in soldering and assembly. When it comes to testing and debugging though, it could get tricky if you have to start handling test probes while looking at the meter display or fiddling with knobs on the oscilloscope. Sometimes one has to test a board that has just pads for test points. Or maybe you need to directly probe pins on an IC. Checking multiple signals on I2C, SPI, Serial or USB is not too easy with just two hands. [Giuseppe Finizia] is an electronic engineer at the Scientific Investigations Department of the Carabinieri in Italy. He works as a senior analyst in the Electronic Forensics Unit and deal’s with technical investigations on seized electronic devices. To help him in his investigative work, he designed and built a 3D printed PCB workstation with octopus-like tentacles that provides all the additional fingers needed.

The tool is basically a base with adjustable clamps where the test PCB can be fixed. Around the base, up to twelve articulated “tentacles” can be fixed. Various test accessories are attached to the ends of these tentacles – Alligator Clips for holding electronic parts, IC Hook Clip Grabbers, Micro SMD Grabber Test Clips and some others that he is still working on. [Giuseppe] used  MOI 3D modeling software to design his device, and the files are available on Thingiverse for download. He does warn that printing all the parts, specially the tentacle units, can be quite tricky on a regular 3D printer. He used a ZORTRAX M200 printer in high resolution mode and Z-HIPS filament. However, it may be easier to just use machine shop flexible coolant pipe for the tentacles. This may require some sort of modification to the base mounts and the business end of the tentacles though.

Thanks to [CFTechno] for sending in this tip.