Here’s a tip from a wizened engineer I’ve heard several times. If you’re poking around a circuit that has failed, look at the resistor color codes. Sometimes, if a resistor overheats, the color code bands will change color – orange to brown, blue to black, and so forth. If you know your preferred numbers for resistors, you might find a resistor with a value that isn’t made. This is where the circuit was overheating, and you’re probably very close to discovering the problem.
The problem with this technique is that you have to look at and decode all the resistors. If automation and computer vision is more your thing, [Parth] made an Android app that will automatically tell you the value of a resistor by pointing a camera at it.
The code uses OpenCV to scan a small line of pixels in the middle of the screen. Colors are extracted from this, and the value of the resistor is displayed on the screen. It’s perfect for scanning through a few hundred through hole resistors, if you don’t want to learn the politically correct mnemonic they’re teaching these days.
Video below, and the app is available for free on the Google Play store.
Continue reading “Reading Resistors With OpenCV”
Here’s a simple piece of equipment which you’ll be proud to display on your electronics bench. It’s a resistance decade box. The concept has been around forever — it offers the ability to tune a wide range of resistance values just by adjusting the controls. We especially like the clean look of this one, and think the use of DIP switches is a nice touch.
Check out the toggle switch at the top. It lets you disconnect the resistance values from the output in order to test them with your meter. It may not seem like much, but fudging your switch settings could end up smoking your target project. The value of that feature isn’t lost on us.
The DIP switches are mounted to some Radio Shack breakout boards which work perfectly for hosting the resistors as well. This keeps the inside of the enclosure nice and tidy. The final touch is the printed face plate applied to the cover of the box.
Like we’ve said, this one is nice but our favorite is still this one that uses thumbwheel switches to dial in a value.
If hardware manufacturers want to keep their firmware crippling a secret, perhaps they shouldn’t mess with Linux users? We figure if you’re using Linux you’re quite a bit more likely than the average Windows user to crack something open and see what’s hidden inside. And so we get to the story of how [Gnif] figured out that the NVIDIA GTX690 can be hacked to perform like the Quadro K5000. The thing is, the latter costs nearly $800 more than the former!
[Gnif] wanted the card for gaming and to support multiple monitors. It has no problem driving up to three screens under Windows. But the Linux drivers only allow this on the professional counterpart to the GTX690, the Quadro K5000. It turns out that the card responds to a device ID as assigned by a series of analog values. These can be tweaked by swapping, yanking, or adding resistors in just the right places. As with that Agilent multimeter unlock of his which we saw a few days ago, he somehow managed to figure out the secret sauce that unlocks the power hidden in this card.
This paper dial makes selecting current limiting resistors a snap. [Giorgos Lazaridis] came up with the tool, which he describes in detail in the Worklog tab of his writeup. If you want one of your own he also posted a PDF which you can print, cut, and tack together.
At this point we can calculate resistor values for LED circuits without looking at reference material. But it wasn’t always like that. This wheel will be a fantastic tool for those just starting out in hobby electronics who are trying to grasp the theory behind lighting up a simple project. The outer wheel references the source voltage, with the inner being a gauge of forward voltage across the LED(s). Line those two values up and you can read the optimal resistor value in the window seen to the right. But wait, there’s more! As you can see in the video after the break the opposite face of the dial also includes a window which will tell you the power dissipation so that you may choose a properly rated resistor. Slick!
Continue reading “Papercraft dial is the slide-ruler of current limiting resistors”
This one might be an oldie, but it’s certainly a goodie.
Way back in 2005, [David] and [Charles] needed a project for one of their engineering courses. With so many loose resistors scattered over the lab, they decided to build an automated resistor sorter (PDF warning) to separate these resistors and put resistors of the same value together in the same bin.
The electrical and programming portion of this build is relatively simple – just a PIC microcontroller reading the value of a resistor. The mechanical portion of this build is where it really shines. Resistors are sorted when they pass through small plastic tubes mounted to a wooden frame.
There are several levels of these tubes in [David] and [Charles]’ sorter that move back and forth. The process of actually sorting these resistors is a lot like going down a binary tree; at each level, the tube can go right or left with the help of a solenoid moving that level of the frame back or forth.
[David] and [Charles]’ project wasn’t entirely complete by the end of the class; to do so would require 8 levels and 128 different tubes on the bottom layer. Still, it worked as a proof of concept. We just wish there was a video of this machine in action.
Tip ‘o the hat to [Alexander] for finding this one and sending it in.
If you’ve ever had to organize a bunch of resistors, you’ll know why [Anthony] created EESpeak. It’s a voice-controlled component look up tool that calculates a component value by listening to you read out color code bands.
In his demo video of EESpeak, [Anthony] reads off the color bands of several resistors whilst the program dutifully calculates and displays the value. [Anthony] also included support for calculating the value of capacitors and inductors by speaking the color bands, as well as EIA-96 codes for SMD parts.
In addition to taking speech input and flashing a component value on the screen, EESpeak also has a text-to-speech function that will tell you what a component without ever having to look at your monitor.
Even though the text-to-speech function seems a little cumbersome – it takes much longer for a computer to speak a value than to display it on the screen – using voice recognition to calculate component values is an awesome idea. With an extremely limited vocabulary the computer has to understand, the error rate of EESpeak is probably very low.
You can check out [Anthony]’s demo video after the break, and of course download the app on his blog.
Continue reading “Sorting resistors with speech recognition”
Here’s a tip to keep in your back pocket, you can use a metal file to adjust your resistors. [Gareth] shows off this technique in the video after the break. A metal file is literally all that you need to do some fine tuning. Just make sure you’re starting off with a carbon film resistor as this will not work with the metal film variety.
His example shows a 10k resistor which is reading just 9.92k on his multimeter. But he needs precisely 10k. After getting through the protective layer he makes just a couple of passes with a small file, each time adding about 20 Ohms of resistance. Now he does mention that excessive deep cuts can hurt the power rating of the resistor. But this certainly isn’t damaging it if done correctly. It turns out this is how they are tuned at the factory.
One possible use he mentions is trimming the balance on a hacked servo motor.
Continue reading “The cool kids all file their resistors for accuracy”