Bode Plots On An Oscilloscope

August 19, 2013 by Brian Benchoff 9 Comments

bode

Bode plots – or frequency response graphs – are found in just about every piece of literature for high-end audio equipment. It’s a simple idea, graphing frequency over amplitude, but making one of these graphs at home usually means using a soundcard, an Excel spreadsheet and a multimeter, or some other inelegant solution. Following a neat tutorial from [Dave Jones], [Andrew] came up with a very simple way to make a Bode plot in real-time with an oscilloscope, a microcontroller, and a few off-the-shelf parts.

The basic idea behind [Dave Jones]’ impromptu Bode plotter is to configure a frequency generator to output a sine wave that ramps up over a period of time. Feed this sine wave through a filter, and you have amplitude on the vertical axis of your ‘scope and frequency on the horizontal axis. Boom, there’s your Bode plot.

[Andrew] did [Dave] one better by creating a small circuit with an Arduino and an AD9850 sine wave generator. Properly programmed, the AD9850 can ramp up the frequency of a sine wave with the Arduino outputting sync pulses every decade or octave of frequency, depending if you want a linear or log Bode plot.

It’s a nifty little tool, and when it comes to building test equipment from stuff that just happens to by lying around, we’ve got to give it up for [Andrew] for his really cool implementation.

Building An Accurate Equal Arm Balance

August 18, 2013 by Mike Szczys 13 Comments

microscale

This interesting take on weights and measures uses a two foot long level as the base for a diy equal arm balance. The balance is the oldest method used for measuring mass. That’s because you don’t even need a reference weight for it to work as long as you are measuring ingredients that are proportional to each other in whole numbers.

The key to accuracy with these scales is to reduce friction at the fulcrum. In this case the fulcrum is made of two upturned razor blades on the base, with a single razor blade resting perpendicular to those on the arm. But because gravity is doing the equalization, the base must be as level as possible. Adjustable feet were added to the base so that it can be leveled on two axes. When the tower at the center was built (using threaded rod) a disc level was used to fine-tune the mounting angle of the two razor blades. The finishing touches include a coupling nut on each end for fine-tuning the balance, and the halves of a tea ball strainer as the weighing vessels.

Repairing A Mill That Cost As Much As A Car

August 8, 2013 by Brian Benchoff 45 Comments

miters

Years ago, someone at the bio-instrumentation lab at MIT needed to change a CMOS battery in the controller for a three axis mill. This reset the machine’s BIOS and was widely regarded as a bad move. The mill sat in the lab for a few years before Prof. [Ian Hunter] donated it to MITERS – the student shop at MIT. And so the task of repairing a machine that cost as much as a car fell upon a plucky group of students.

The machine – a Dyna-Myte 1007 has a 10″x7″x10″ work area, pneumatic tool changers and carousel, and the working for a fourth axis. It is. however, driven by an ancient Pentium computer running DOS with all the fun of ISA slots and IRQs that entails.

The MITERS began their repair by digging around in the software configuration, finding the axis drive is controlled via IRQ 3, which was currently occupied by COM 2. Changing that in the BIOS let the computer control the axes and, with a few solenoids and an air compressor, the tool carousel also worked.

With a bit of digging around, the MITERS also got the spindle working, giving them a very awesome and very expensive CNC milling machine for free. Even though the computer could be replaced with a $35 Raspberry Pi, we really have to admire the MITERS for fixing what they already had; it’s a cheaper and much, much faster way to get their new toy up and running.

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Supercharging Your Digital Calipers

August 8, 2013 by Marsh 56 Comments

supercapCalipers01

A dead battery in your digital calipers usually means a trip to the store for a new button cell. Not for [Trevor]. His hack substitutes a super capacitor, guaranteeing you’ll never need to rummage around for one of those pesky watch batteries again.

These calipers require only 20 seconds to reach a full charge that can last for a few days. Better still, [Trevor] designed a simple circuit with a voltage regulator at the end of the cord to allow charging via USB: just remember to flip the switch from “discharging” to “charging” mode. Although this is a fairly straightforward hack, its design is impressively tidy. The super capacitor fits perfectly at the end of the display and slides along with it, keeping it away from any important printed numbers. If these are the same calipers everyone seems to have these days, it looks like it may still fit in the provided case, too.

If you’re looking for more ways to beef up your calipers, try upgrading them with a Bluetooth module.

Taming STM32 Discovery Boards For Regular Use

August 7, 2013 by Mike Szczys 6 Comments

taming-discovery-boards

We think [Karl Lunt] has a point when he says that the STM32 Discovery Boards are cool and inexpensive, yet not hobby friendly. But it’s nothing that a little big of creativity can’t solve. Above are pictured three of the hacks he used to tame the Discovery boards.

The first is the addition of a microSD card adapter. He soldered wirewrap wire to each of the contacts on the adapter. He recommends a low iron setting to make sure you don’t melt the plastic adapter housing. He then used double stick foam tape to adhere it to the bottom of the dev board. The other ends of the wire are wrapped around the appropriate pins on the dual-row pin header. Similarly, the UART3 connections are broken out from the pin headers to that white quick connect socket. This lets him access serial data without having to solve the USB issues that were vexing him.

Finally, he made his own daughter board to break out the dual row headers into screw terminals. We’ve been hit with problems interfacing hardware with the board’s native connections — jumpering to IDE cables just never worked reliably. This breakout board not only makes it simple, but organizes the pins into groups based on their alternate functions.

Do you remember seeing the hacksaw version of this Discovery board which gives you two dev boards for the price of one?

Replacing Knurled Thumb Screws

August 6, 2013 by Brian Benchoff 32 Comments

Screw

[Pete] bought himself an old South Bend lathe, but unfortunately some of the thumb screws were missing from this fine old machine. Originally, the lathe had knurled thumbscrews, and with a thumbscrew from Ace hardware the lathe itself was functional, but by no means looking its best. With a lathe you can make just about anything, so [Pete] decided he would make his own knurled thumbscrews and bring this lathe back to life.

Knurling is a diamond or linear pattern of indentations usually found on fancy metal knobs, flashlights, and other equipment that needs a good grip. While there are knurling tools for lathes, [Pete] decided to use his knurlmaster – a handheld device that looks like a pipe cutter – to cut a few knurls into a steel bar.

As for making this knurled bar into a proper thumbscrew, [Pete] shows us two methods: the first is tapping the knurled steel, putting in the right screw for the job, and securing the parts with Loctite. The second method involves cutting the threads on the lathe, an excellent example of how a lathe can make just about anything, even parts for itself.

Bench Equipment Tip: Screenshot Of Old Oscilloscopes

August 6, 2013 by Mike Szczys 18 Comments

oscillocam-oscilloscope-camera-accessory

Here’s a quick tip on capturing the output of oscilloscopes that don’t have that native feature. [Paulo Renato] used a cookie tin as a camera cowl for capturing CRT oscilloscope screenshots.

We figure if you’ve got any kind of functioning oscilloscope you’re lucky. And although it’s nice to pull down the measurements to your PC on the newer models, the results [Paul] gets with this rig are still satisfactory. The plastic cookie box he used blocks out ambient light while holding the camera at a consistent focal length. He used some flat black spray paint to make sure the obnoxious yellow plastic didn’t interfere with the image, then drilled a hole which fits tightly around his camera lens.

You’ll need to monkey with the exposure settings to get the best image. But once you’ve got it dialed in it should be the same every time you want to take a picture of the screen.