Need A Nano-Ammeter? You Already Have One!

February 1, 2016 by Al Williams 23 Comments

[Dannyelectronics] sometimes needs to measure tiny currents. Really tiny, like leakage currents through a capacitor. He’s built a few setups to make the measurements, but he also knew he’d sometimes want to take readings when he didn’t have his custom gear available. So he decided to see what he could do with an ordinary digital meter.

As you might expect, a common digital meter’s current scales aren’t usually up to measuring nano- or pico-amps. [Danny’s] approach was not to use the ammeter scale. Instead, he measures the voltage developed across the input impedance of the meter (which is usually very high, like one megaohm). If you know the input characteristics of the meter (or can calibrate against a known source), you can convert the voltage to a current.

For example, on a Fluke 115 meter, [Danny] found that he could read up to 60nA with a resolution of 0.01nA. A Viktor 81D could resolve down to 2.5pA–a minuscule current indeed.

We’ve looked at the difficulties involved in reading small currents before. If tiny currents aren’t your thing, maybe you’d like to try charging an iPhone with 3 KA, instead.

LED Tester Royale

January 29, 2016 by Elliot Williams 33 Comments

What do you get for the geek who has everything and likes LEDs? A tricked-out LED tester, naturally. [Dave Cook]’s deluxe model sports an LCD screen and two adjustable values: desired current and supply voltage. Dial these in, plug in your LED, and the tiny electronic brain inside figures out the resistor value that you need. How easy is that?

An LED tester can be as easy as a constant-current power supply, and in fact that’s what [Dave]’s first LED tester was, in essence. Set an LM317 circuit up to output 10mA, say, and you can safely test out about any LED. Read off the operating voltage, subtract that from the supply voltage, and then divide by your desired current to figure out the required resistor. It only takes a few seconds, but that’s a few seconds too many!

The new device does the math for you by adding an AVR ATtiny84 into the mix. The microcontroller reads the voltage that the constant current supply requires, does the above-mentioned subtraction and division, and displays the needed resistor. So simple. And as he demonstrates in the video below, it does double-duty as a diode tester.

This is a great beginner’s project, and it introduces a bunch of fundamental ideas: reading the ADC, writing to an LED screen, building a constant current circuit, etc. And at the end, you have a useful tool. This would make a great kit!

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Two Portable Oscilloscopes: Shootout

January 28, 2016 by Al Williams 3 Comments

Last time I introduced you to two relatively inexpensive and somewhat portable scopes: the EM125, which is a cross between a digital voltmeter and an oscilloscope, and the Wave Rambler, which is a scope probe with a USB connector attached. Both of the devices cost about $100, and both have their plusses and minuses.

This time, though, I wanted actually to look at some real-world signals. To make that easy, I grabbed yet another scope-like thing I had handy: an Embedded Artists Labtool. This is an interesting board in its own right. It is an LPC-Link programmer attached to an LPC ARM board that has several high-speed A/D channels. However, I’m not using any of that capability for now. The board also has a cheap ARM processor (an LPC812) on it that serves only to generate test signals. The idea is you can use the Labtool in a classroom with no additional equipment.

The Labtool’s demo CPU generates a lot of different signals, but with only one channel on the test scopes, it didn’t make sense to look at, for example, I2C data. So I stuck with two different test signals: a varying pulse width modulation signals and a serial UART transmitter.

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A Tale Of Two (Sub $100) Oscilloscopes

January 27, 2016 by Al Williams 44 Comments

Hi, I’m Al, and I’m an oscilloscope-holic. Just looking around my office, I can count six oscilloscope or oscilloscope-like devices. There are more in my garage. If you count the number of scopes I’ve owned (starting with an old RCA scope with a round tube and a single vertical scale), it would be embarrassing.

On the other hand, if you are trying to corral electrons into doing useful things, a scope is a necessity. You can’t visualize what’s happening in a circuit any better than using an oscilloscope. Historically, the devices were expensive and bulky. I’ve had many Tektronix and HP scopes that stayed in one place, and you brought what you were working on to them (sometimes called a “boat anchor”). It wasn’t that long ago that one of my vintage Tek scopes had its own dedicated cart so I could wheel it to where it was needed.

These days, scopes are relatively cheap, depending on what you have in mind for performance. They are also highly portable, which is nice. In fact, it is an indication of how spoiled I’ve become that my main bench scope–a Rigol DS1104Z–weighs seven pounds, yet I still look for something smaller for quick jobs.

That’s how I came into possession of two cheap scopes I wanted to talk about. They are similar in ways but different in others. Neither are going to replace a real bench scope, but if you want something portable, or you are budget-limited, they might be worth a look.

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Repair And Calibration Of Valhalla Programmable Precision Standard

January 25, 2016 by Anool Mahidharia 5 Comments

Precision standards are the pinnacle of test and measuring instrumentation. Well engineered, sure, but also beautifully built and a feast to look at, no matter how old they are. [Shahriar] at “The Signal Path” often gives us the skinny on such equipment. In the latest episode, we get a look inside a Valhalla 2701C Programmable Precision DC Voltage Standard.

Even by 1990 standards, it is a fairly basic instrument, capable of producing just DC Voltages from 100nV up to 1200V. But it is a reference standard, so the output is highly stable, accurate and precise. He snagged it from eBay on the cheap but transport seemed to have caused some damage. It would switch on and relays would click when he pressed buttons, but the 7-segment LED display was blank. Luckily, opening the top cover fixes that problem – just a loose connection between the front display and the main board. Examination also shows that adding a 120mA DC current range would require adding additional components on the main board so his hope of doing a quick firmware upgrade is short lived.

[Shahriar] takes the opportunity to walk us through the various sections of the well built unit. It’s apparently seen some repairs during it’s life. A few capacitors look changed, and a relay housing has seen damage from a soldering iron. The digital section is mainly the 6800 micro controller, an EPROM and a NVRAM, and it generates the PWM signals needed for producing the output voltages. A highly precise reference signal is essential for such equipment, and this one uses the LM299 with a “custom” suffix meaning it was specially screened and binned. He does a quick calibration run, but it’s obviously rushed and doesn’t produce stable results. But that could also be due to the low quality cables he used, or a number of other factors. Calibrating such equipment is a job demanding both time and patience.

While this may not knock your socks off. For that, check out this post where [Shahriar] does a tear down of the one million dollar Labmaster 10-100zi Oscilloscope, or this other one where he plays around with a half a million dollar oscilloscope you’ll probably never use, much less own.

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Let’s Play…Wheel Of Solder!

January 22, 2016 by George Graves 43 Comments

Solder is solder right? Just spin the wheel and whatever comes up will work fine. Well, not so fast. If you’re new to electronics, or are looking at getting started, there is a bit to learn first. [Mr Carlson] has the info you need with this youtube video you can watch after the break.

He begins with a discussion of solder diameter. For most through hole work, something around 0.03 inch is pretty universal. When your ready to step up to SMD work, we find 0.02″ inch to be a much better match to the smaller pad sizes. [Mr Carlson] goes on to talk about the types of flux used inside the solder. Rosin(R), Rosin-Midly-Activated(RMA) and Rosin Activated(RA) in order of least to most aggressive.

He rounds out the video with information and a warning about using “organic” core solder. If you’re new to the world of solder, this video is a good jumping off point. TLDR; If you’re just starting out, a 0.03″ RMA solder would be a good place to start – but if you want to learn a bit more, the 20 minute video is worth the watch for those of you just getting your ~~feet~~ iron tip wet. It’ll serve you well at least until solderless metal glue becomes affordable.

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Link Trucker Is A Tiny Networking Giant

January 22, 2016 by Elliot Williams 17 Comments

If you’re a networking professional, there are professional tools for verifying that everything’s as it should be on the business end of an Ethernet cable. These professional tools often come along with a professional pricetag. If you’re just trying to wire up a single office, the pro gear can be overkill. Unless you make it yourself on the cheap! And now you can.

[Kristopher Marciniak] designed and built an inexpensive device that verifies the basics:

Is the link up? Is this cable connected?
Can it get a DHCP address?
Can it perform a DNS lookup?
Can it open a webpage?

What’s going on under the hood? A Raspberry Pi, you’d think. A BeagleBoard? Our hearts were warmed to see a throwback to a more civilized age: an ENC28J60 breakout board and an Arduino Uno. That’s right, [Kristopher] replicated a couple-hundred dollar network tester for the price of a few lattes. And by using a pre-made housing, [Kristopher]’s version looks great too. Watch it work in the video just below the break.

Building an embedded network device used to be a lot more work, but it could be done. One of our favorites is still [Ian Lesnet’s] webserver on a business card from way back in 2008 which also used the ENC28J60 Ethernet chip.
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