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.

[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.

[Alex]‘s used OpenCV for processing of the image data. The app works by scanning the image from the top-left corner and continuing until it sees a beige rectangle. After a bounding box is drawn around the resistor, the iPhone scans the image for columns of color. After a little interpretation, the value of the resistor is displayed on the screen. While it only works on resistors with beige plastic now, [Alex] says he’ll expand that in the future to include blue bodied metal-oxide resistors. [Alex] says the coding only took a week, so if anyone would like code a similar app for Android, be sure to tell us on our tip line.

This isn’t [Alex]‘s first Hack A Day build. We featured his Handy Board project that uses an NES controller to play some chiptunes earlier this summer. Compared to the projects we’ve let slip over the last few months, it’s good to see someone did something productive with their summer.

[Alex] posted a demo of his resistor app on YouTube. Check it out below.

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.

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.

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]

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.

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]

adafruit industries’ latest product is an adjustable breadboard power supply kit. We’ve seen breadboard supplies before, but like most of adafruit’s kits, this is the best design you’re going to encounter. It uses an MIC2941 voltage regulator instead of the more commonplace LM317. It has a very low dropout which means your output voltage can be much closer to the input voltage. Their example is using 3AAA or a Li-Ion battery for an output of 3.3V. Input can be through a barrel jack or terminal blocks. There is a selection switch for 3.3, 5, and adjustable voltage. Using the adjustment pot you can select an output voltage anywhere from 1.3V to within .5V of the 20V maximum input. The adjusted output voltage will remain the same even if you increase the input voltage. Like all of their kits, you can find schematics, assembly and usage instructions, on their project site.

Update, Saturday July 4th, 2009: All preorders are closed.

We’re excited to announce our partnership with the folks at Seeed Studio (home of the excellent Seeeduino) to put the Bus Pirate v2go into production! The preorder period ends July 3rd. The price is $30 including worldwide shipping. The board pictured above is a hand soldered prototype, but the ones sold by Seeed are completely factory assembled.

This is the first officially produced piece of Hack a Day hardware. Depending on its success, we’ll be able to put many future designs into production. Read more about the Bus Pirate in our latest How-to. Thank you for your support!

***Update, Monday June 29, 2009: Wow, your support has been overwhelming! Thank you! There have been more orders for the Bus Pirate than we ever imagined. As of this update, there’s a few (12) Bus Pirates left in the Seeed preorder. After that, we’ve exhausted the supply of PIC24FJ64GA002s available in Shenzhen. If you’ve already placed your order nothing changes, the manufacturing process has already begun and your Bus Pirate will ship ASAP.

After the first preorder is filled, Seeed will start a new preorder. The second preorder will be delayed until more PIC24FJ64GA002s are delivered, about 4 to 6 weeks. This order should ship about 6 to 8 weeks after July 3, 2009, but we’ll try our best to get it out sooner. Thank you again for your support!

Those of you that live in snowier climates will drool over the I-Shovel, a battery powered robot that shovels the snow off your driveway, saving you countless hours of backbreaking labor over the course of a single winter. Its inventors claim that, despite its relatively underpowered motor, it keeps the driveway clear even in heavy snowfall; the trick, apparently, is that the robot constantly monitors the amount of snow on the driveway and springs into action whenever a significant but manageable layer has built up. Unfortunately, the I-Shovel is still a prototype, but with any luck you’ll be able to actually buy one soon. If you’re impatient, of course, you could always try building your own.

[via Toolmonger]

Scrawlr is the latest tool to come out of HP’s Web Security Research Group. It was built in response to the massive number of SQL injection attacks happening on the web this year. Most of these vulnerable sites are found through googling, so Scrawlr works the same way. Point it at your web server and it will crawl all of the pages and evaluate the URL parameters to see if they’re vulnerable to verbose injection. It reports the SQL server and table names if it comes across anything.

It only supports 1500 pages right now and can’t do authentication or blind injection. It’s still a free tool and a great way to identify if your site is vulnerable to automated tools finding you website via search engines.

[via Acidus]