Every once in a while we get wind of a project that we’re reluctant to write up for the simple reason that it looks too good to be true. Not that projects need to be messy to be authentic, mind you, but there are some that are just so finished and professional looking that it gives us a bit of pause. [Sebastian]’s programmable precision resistor is a shining example of such a project
While [Sebastian] describes this as “a glorified decade resistance box,” and technically that’s exactly right — at its heart it’s just a bunch of precision resistors being switched into networks to achieve a specific overall resistance — there’s a lot more going on here than just that. The project write-up, which has been rolling out slowly over the last month or so, has a lot of detail on different topologies that could have been used — [Sebastian] settled on a switched series network that only requires six relays per decade while also minimizing the contribution of relay contact resistance to the network. Speaking of which, there’s a detailed discussion on that subject, plus temperature compensation, power ratings, and how the various decades are linked together.
For as much that’s interesting about what’s under the hood, we’d be remiss to not spend a little time praising the exterior of this instrument. [Sebastian] appears to have spared no expense to make this look like a commercial product, from the rack-mount enclosure to the HP-esque front panel. The UI is all discrete pushbuttons and knobs with a long string of 16-segment LEDs — no fancy touch-screens here. The panel layout isn’t overly busy, and looks like it would be easy to use with some practice. We’d love to hear how the front and rear panel overlays were designed, too; maybe in a future project update.
This honestly looks like an instrument that you’d pay a princely sum to Keithley or H-P to own, at least back in the late 1990s or so. Kudos to [Sebastian] for the attention to detail here.
With surface-mount components quickly becoming the norm, even for homebrew hardware, the resistor color-code can sometimes feel a bit old-hat. However, anybody who has ever tried to identify a random through-hole resistor from a pile of assorted values will know that it’s still a handy skill to have up your sleeve. With this in mind, [j] decided to super-size the color-code with “The Great Resistor”.
At the heart of the project is an Arduino Nano clone and a potential divider that measures the resistance of the test resistor against a known fixed value. Using the 16-bit ADC, the range of measurable values is theoretically 0 Ω to 15 MΩ, but there are some remaining issues with electrical noise that currently limit the practical range to between 100 Ω and 2 MΩ.
[j] is measuring the supply voltage to help counteract the noise, but intends to move to an oversampling/averaging method to improve the results in the next iteration.
The measured value is shown on the OLED display at the front, and in resistor color-code on an enormous symbolic resistor lit by WS2812 RGB LEDs behind.
Precision aside, the project looks very impressive and we like the way the giant resistor has been constructed. It would look great at a science show or a demonstration. We’re sure that the noise issues can be ironed out, and we’d encourage any readers with experience in this area to offer [j] some tips in the comments below. There’s a video after the break of The Great Resistor being put through its paces!
For prototype electronics projects, most of us have a pile of resistors of various values stored somewhere on our tool bench. There are different methods of organizing them for easy access and identification, but for true efficiency a resistance substitution box can be used on the breadboard to quickly change resistance values at a single point in a circuit. Until now it seemed this would be the pinnacle of quickly selecting differently-sized resistors, but thanks to this programmable resistor bank there’s an even better option available now.
Unlike a traditional substitution box or decade box, which uses switches or dials to select different valued resistors across a set of terminals, this one is programmable and uses a series of sealed relays instead. That’s not where the features stop, though. It also comes equipped with internal calibration circuitry which take into account the resistance of the relay contacts and internal wiring to provide a very precise resistance value across its terminals. It’s also able to be calibrated manually to account for temperature or other factors.
For an often-overlooked piece of test equipment, this one surely fits the bill of something we didn’t know we needed until now. Even though digital resistor substitution boxes are things we have featured in the past, the connectivity and calibration capabilities of this one make it intriguing.
Some people look at a venerable resource like resistor color code charts and see something tried and true, but to [Andrew Jeddeloh], there’s room for improvement. A search for a more intuitive way is what led to his alternate cheat sheet for resistor color codes.
Color code references typically have a reader think of a 560 kΩ resistor as 56 * 10 kΩ, but to [Andrew], that’s not as simple as it could be. He suggests that it makes more sense for a user to start with looking up the colors to make 5.6 (green-blue), then simply look up that a following yellow band means resistance in the 100 kΩ range (assuming a four-band resistor); therefore 560 kΩ is green-blue-yellow.
The big difference is that the user is asked to approach 560 kΩ not as 56 * 10 kΩ, but as 5.6 * 100 kΩ. [Andrew] shares a prototype of a new kind of chart in his post, so if you have a few minutes, take it for a spin and see what you think.
The vast majority of us are satisfied with a standard, base ten display for representing time. Fewer of us like to be a bit old-fashioned and use a dial with a couple of hands that indicate the time, modulo twelve. And an even smaller minority, with a true love for the esoteric, are a fan of binary readouts. Well, there’s a new time-telling game in town, and as far as we’re concerned it’s one of the best ones yet: resistor color codes.
You can set the time in the traditional fashion using buttons, or — and here’s the brilliant part — you can use a resistor. Yup, that’s right. Connecting a 220 Ohm resistor across two terminals on the clock will set the time to 2:20. Genius.
When you come across an art as old as timekeeping, it’s easy to assume that everything’s already been done. We have sundials, hourglasses, analog clocks, digital watches, those cool clocks that use words instead of numbers, the list goes on. That’s why it’s so exciting to see a new (and fun!) idea like this one emerge.
We’re always fans of interesting clock builds around here, whether it’s a word clock, marble clock, or in this case a clock using a unique display method. Of course, since this is a build by Hackaday’s own [Moritz v. Sivers] the display that was chosen for this build was a custom thermochromic display. These displays use heat-sensitive material to change color, and his latest build leverages that into one of the more colorful clock builds we’ve seen.
The clock’s display is built around a piece of thermochromic film encased in clear acrylic. The way the film operates is based on an LCD display, but using heat to display the segments. For this build, as opposed to his previous builds using larger displays, he needed to refine the method he used for generating the heat required for the color change. For that he swapped out the Peltier devices for surface mount resistors and completely redesigned the drivers and the PCBs around this new method.
Of course, the actual clock mechanism is worth a mention as well. The device uses an ESP8266 board to handle the operation of the clock, and it is able to use its wireless capabilities to get the current time via NTP. All of the files needed to recreate this are available on the project page as well, including code, CAD files, and PCB layouts. It’s always good to have an interesting clock around your home, but if you’re not a fan of electronic clocks like this we can recommend any number of mechanical clocks as well.
The best part is that the status can been seen on both sides of the door so you don’t forget to keep it updated. Or maybe it’s the super-low part count. There’s no BLE, LoRa, or Wi-Fi, just two sets of red and green LEDs, a three-way switch, and a power source. Well, and current-limiting resistors of course.
[Bob] already had all the components on hand, including the nifty enclosure, which is another great thing about this build. Like [Bob] says, you could house the control side of this circuit in just about anything you’ve got lying around.