From the readers: low battery cutoff solutions

We got a lot of really great feedback about low battery cutoff options in the comments section of Monday’s replacement battery post. To refresh your memory, some power tool batteries were replaced by Lithium Polymer units which can be damaged if drained too low before recharging. We had thought that many Lithium cells had cutoff circuitry these days. The consensus is that these batteries didn’t because they’re for RC applications where weight is an issue. But we did get a ton of people sending in commercially available drop-in solutions, mostly from RC hobby outlets, so search around for those if you’re interested.

[Christopher] sent us a link to the cutoff circuit he built for his bike light. You can see the schematic for it above (direct link). He sourced an ATtiny45 to drive a MOSFET which disconnects the battery when it gets too low. This would be easy to adapt to other uses, but note that there’s a voltage regulator involved as well as a few other passives… not a difficult solution but also not all that simple.

This same concept can be adapted. A few commentors mentioned using a transistor (or MOSFET) with the base driven by a voltage divider including a zener diode. This way the voltage rating of the diode would effectively shut off the gate when that threshold was reached.

We also enjoyed reading about [Bill's] human-controlled cutoff circuit. It also uses a zener diode, but this time in series with a resistor and and LED patched into the trigger of the tool. The LED will shine brightly when the battery is in good shape. It will dim near the end, and fail to light when the critical limit has been reached. Just make sure you’re paying attention and you’re in good shape.

Ohm Sense makes sense of resistor color bands

[Alex Busman]‘s first foray in iOS programming looks like a pretty useful tool. He came up with Ohm Sense, an iPhone app that will take a picture of a resistor and calculate the value based on the color bands. It’s a great tool that we wish we had when we were starting out. At 99 cents, the app is also much cheaper than the emotional cost of our relationship with Violet.

[Read more...]

Homebrew heat gun from scrounged parts

A Hack a Day reader needed a tool to solder a lot of SMD parts, so he built a DIY heat gun, and we’re impressed with the results.

After trawling the internet looking for ideas for his heat gun, [MRGATZ85] found that most builds used the ceramic element from cheap soldering irons. Experiments in this direction didn’t go very well because the ceramic element in these irons tends to fall apart very easily. In a moment of inspiration, [MRGATZ85] realized he had an old vaporizer lying around and decided to take it apart. To his surprise, the vaporizer element was a great size, self-contained, and most importantly free. After fabricating a case out of high-temperature foam, aerosol cans, and deadbolt parts, [MRGATS85] was left with a very nice build.

Aside from SMD work, a heatgun can be a very valuable tool for PCB stripping and being used for solder reflow. We’re a little surprised we haven’t seen a homebrew heat gun in quite a while. Even though the element is surrounded by high-temperature foam, the gun still gets a little hot to the touch. We’re hoping that will eventually be under control; it’s a very useful build otherwise.

Check out the image gallery, or the video demo after the break.

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Variable capacitance/reistance switch box has you covered


While working on electronics projects, it’s often necessary to test out different capacitance or resistance values as things are moving along. Depending on what you are testing, this can be a tedious process even when using a breadboard. Instructables user [mattthegamer463] recently built a very useful device that would help out in these situations, and would likely be a welcome addition to any Hackaday reader’s workbench.

His variable resistor/capacitor box makes it easy to test out any number of different resistance or capacitance values with a simple turn of a knob. He wired up a pair of pots to provide a wide range of resistance values, being sure to add a low-resistance safety as well as safety override switch for those of you who like to have things blow up in your face live dangerously. A set of 22 capacitors were wired up on a piece of perfboard, each of which can be selected using a pair of knobs. He added a simple switch to allow the capacitors to be toggled between parallel and series orientations as well.

[Matt] did a wonderful job here – this is a great project that can be customized in a multitude of ways to fit almost anyone’s specific needs.

9 digit pulse counter

At roughly $20 to build, this 9 digit pulse counter is an excellent example of home built tools. The builder, [Josh] found himself repairing a device and in need of a pulse counter. With the components cheaply available, he just built his own. He says that it has a few limitations, like display brightness, but overall it seems to do the job well. You can download the PCB from his site.

[via MakeZine]

Tim “The Tool Man” Taylor’s dream ride

While surfing one of our favorite websites, we came upon this little jewel. We can’t really tell if this is hack-worthy, or just a deathtrap, so to help decide…

Mechanics crawler + 80cc motor – safety concerns = deathtrap

It’s really that final “Brakes? Why would I need to stop?” that puts this project over the edge. Regardless, check out a video after the break. And please, do not try this at home.

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Dresser tool chest isn’t as ghetto as you’d think


A dedicated rolling chest for one’s tools is among the most indulgent yet worthwhile acquisitions. Having everything mobile and organized for quick access improves efficiency and keeps the shop tidy. But holy living crap, have you priced these things? Even a mediocre setup costs more than the gross national product of some small nations!

Here’s a project that tarts up a dresser into a passable tool chest. Using casters, modern drawer pulls and a tidy paint job, they turn a nasty old dresser into something presentable. It’s nowhere near as slick as the commercial units…no ball bearing glides, not chemical resistant, and your macho grease monkey friends will just roll their eyes…but if you’d rather spend your hard-earned money on more and better tools than a pretty box to put them in, this might be just the thing. From across the room, you’d hardly know the difference.

A good tool chest will include several shallow drawers so that all the tools are visible at a glance and not buried in a jumble. If searching for a piece of furniture to re-use, look for something with multiple slim drawers rather than just a few deep ones; a large jewelry chest might work well.

[via Craftynest]