Digital Decade Resistance Box on the Cheap


[Stynus] has finished a unique decade resistance box which doesn’t use conventional rotary switches to select the appropriate resistors. These switches are old fashioned and expensive, so [Stynus] built this decade resistance box that uses a microcontroller and a series of relays to switch the resistors.

Simply selecting a resistance on the screen tells the microcontrollers which resistors need to be switched in order to provide the proper resistance. The box uses relays to do switching instead of transistors because the transistors don’t handle high frequency AC as well as the relays. The device is powered by an 18V transformer and rectifier and, as a bonus, [Stynus] got all of his parts on the cheap which made this a great solution to the expensive resistance decade box problem.

This is a very well-polished piece of test equipment. We’ve featured other decade resistance boxes but never one that was controlled by a microcontroller. All of the PCB layouts and the code for microcontroller are available on the project site if you have a desire to make your own.

Voltset Multimeters at World Maker Faire


Many tents at World Maker Faire were divided up into booths for companies and various projects. In one of these tents, we found the Voltset booth. [Tom, Ran, and Michael] were on hand to show off their device and answer any questions. Voltset is essentially a multimeter which uses your phone as a display. It connects to an Android phone via USB or an optional Bluetooth module.

Now we’d be a bit worried about the risk of damaging our phones with a voltmeter electrically connected via USB. However, many people have an old phone or retired tablet kicking around these days, which would be perfect for the Voltset. The Bluetooth module alleviates this problem, too – though it doesn’t fix the issue of what happens to the multimeter when someone decides to call.

Voltset isn’t new; both the Voltset team and the similarly specced  Mooshimeter were also at World Maker Faire last year. In the interim, Voltset has had a very successful Kickstarter. The team is accepting pre-orders to be shipped after the Kickstarter backers are sent their rewards.

voltset-2[Tom] told us that the team is currently redesigning their hardware. The next generation prototype board with more protection can be seen in the far right of the top photo. He also mentioned that they’re shooting for 5 digits of accuracy, placing them on par with many bench scopes. We’re skeptical to say the least about 5 digits, but the team is definitely putting their all into this product. We’ll wait until the Kickstarter backers start getting their final devices to see if Voltset is everything it’s cracked up to be.

Cheap Multimeter Gauges Embedded Idle Time


How often is your microcontroller actually doing something? You can find out by measuring idle time, but how exactly do you do this? [Jack Ganssle] shows that simple embedded applications can toggle a pin when idle, which can then be measured. More complex applications like those using a Real Time Operation System can do the same by making use of the idle hook. But what can you do to make this toggling pin feedback actually mean something?

His solution is to repurpose an analog multimeter. The meter is interface with the toggle pin and a trimpot calibrates the needle. This way the needle jumps when the processor is busy and returns to zero when idle. What a great tip for getting a little more feedback about what’s going on inside of that black plastic IC package. It’s not surprising to find such a clever hack from one of the Hackaday Prize judges.

While you’re in the analog multimeter aisle you might want to pick up a couple of extras for more alternate data displays.

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Digital Caliper Sacrificed For DRO Project


In general, machining metal on a lathe or mill takes skill and patience as the accuracy of the cuts are important. To make those accurate cuts, it is important to know where the tool is located and how far it moves. For manual machines, the most basic method of determining position is by using graduated dials mounted on the hand cranks. Although these graduated dials can certainly be accurate, they may be difficult to see and they also require the operator to do math in their head on the fly with every full revolution of the dial. Another option would be a digital read out (DRO) which has an encoder mounted to the moving axes of the machine. This setup displays the exact position of the tool on an easy to read numeric display.

Professional DRO kits for mills and lathes can cost between a few hundred dollars to several thousand dollars.  [Robert] has a lathe, wanted a DRO but didn’t want to shell out serious cash to get it. He built his own for super cheap in an extremely resourceful way…. using a Harbor Freight Digital Caliper. A housing was first fabricated so that the added equipment would not hinder the axis travel of the lathe. The caliper was then cut to length, installed in the housing and the entire assembly was then mounted to the lathe.

DIY Lathe DROIt is totally reasonable to use the stock caliper display to read the positional information, however, even these cheap digital calipers have connections for the encoder output data, which can easily be read by a microcontroller. That means it is super simple to hook these low-cost digital calipers up to a display remotely located in a more convenient position.


Pick and Place Machines at Maker Faire

A few years ago, every booth at a Maker Faire had a 3D printer. It didn’t matter if 3D printing was only tangental to the business, or even if the printer worked. 3D printers have finally jumped the shark, and there’s going to be an awesome t-shirt to reflect this fact. This year there weren’t many 3D printers, leaving us asking ourselves what the new hotness is.

Pick and place machines. We couldn’t find many at the faire, and only Carbide Labs’ Pick and Paste machine was working on picking up small resistors and LEDs the entire faire. Carbide’s Pick and Paste machine is exactly what you would expect in a pick and place machine: it picks up components out of tapes and wells, orients them correctly, and plops them down on a board.

The killer feature for the Pick and Paste is its modular design. The toolhead is expandable, allowing anyone to add a second vacuum nozzle to double the rate parts are placed, or a solder paste dispenser. The guys didn’t have the paste dispenser working for the fair (leaded solder and kids don’t mix), but this machine is effectively a combination pick and place machine and solder paste dispenser, something that’s usually two machines on an assembly line.

Also at the faire was Tempo Automation. They’re in a pseudo-stealth mode right now, waiting until everything works perfectly until bringing their machine to the masses. It is, however, exceptionally fast and about a third of the price of a similar machine.

The only other pick and place machine at the faire was the Firepick Delta, one of the more popular projects on and one of fifty finalists for the Hackaday Prize. Unfortunately, the FirePick Delta was broken in shipping, and although [Neil] was sitting right next to the 3D printing guys, it would have taken all weekend to repair the machine.

CircuitMaker from Altium

Altium recently announced CircuitMaker, their entry into the free/low-cost PCB design tool market. They’re entering a big industry, with the likes of Eagle, KiCad, gEDA, and a host of other tool suites. We had a few minutes to talk with Max in the Altium booth at World Maker Faire, and even got a bit of time with the tool itself.

Hands on, it definitely has the look and feel of Altium Designer, right down to the familiar yellow and green boxes for schematic and sheet parts. Center stage was the 3D view, a feature which Altium has had in their software since the late 90’s.

CircuitMaker’s website is pushing the collaboration aspect of the software. Design choices can be reviewed and commented on in real-time. This also suggests that the data files will live in Altium’s own cloud storage system.

CircuitMaker is still in the pre-beta phase, but they’re looking for beta testers now, so head over to the site and sign up!

Making an Inductor Saturation Current Tester

inductor saturation tester

[Kalle] tipped us about a quick project he made over a couple of evenings: an inductor saturation current tester. All the components used for it were salvaged from a beefy telecom power supply, which allows the tester to run currents up to 100A during 30us in the inductors to be characterized.

Knowing the limits of an inductor is very convenient when designing Switch Mode Power Supplies (SMPS) as an inadequate choice may result in very poor performances under high loads. [Kalle]‘s tester simply consists in a N-Mosfet switching power through a load while a shunt allows current measurements. The saturation point is then found when the current going through the inductor suddenly peaks. As you can see from the picture above, 16 4700uF electrolytic caps are used to compensate for the sudden voltage drop when the Mosfet is activated. A video of the system in action is embedded after the break.

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