High Precision Analog IO With Digital Pins

Reading the temperature of your environment is pretty easy right? A quick search suggests the utterly ubiquitous DHT11, which speaks a well documented protocol and has libraries for every conceivable microcontroller and platform. Plug that into your Arduino and boom, temperature (and humidity!) readings. But the simple solution doesn’t hit every need, sometimes things need to get more esoteric.

The technique summarized by an image from Microchip Appnote AN685

For years we’ve been watching [Edward]’s heroic efforts to build accessible underwater sensing hardware. When we last heard from him he was working on improving the accuracy of his Arduino’s measurements of the humble NTC thermistor. Now the goal is the same but he has an even more surprising plan, throw the ADC out entirely and sample an analog thermistor using digital IO. It’s actually a pretty simple trick based on an intuitive observation, that microcontrollers are better at measuring time than voltage. 

The basic circuit

The circuit has a minimum of four components: a reference resistor, the thermistor, and a small capacitor with discharge resistor. To sense you configure a timer to count, and an edge interrupt to capture the value in the timer when its input toggles. One sensing cycle consists of discharging the cap through the discharge resistor, enabling the timer and interrupt, then charging it through the value to measure. The value captured from the timer will be correlated to how long it took the cap to charge above the logic-high threshold when the interrupt triggers. By comparing the time to charge through the reference against the time to charge through the thermistor you can calculate their relative resistance. And by performing a few calibration cycles at different temperatures ([Edward] suggests at least 10 degrees apart) you can anchor the measurement system to real temperature.

For all the gory details, including tips for how to save every last joule of energy, check out [Edward]’s post and the Microchip appnote AN685 he references. Besides this series [Edward]’s Cave Pearl Project has already yielded an impressive number of Hackday posts. For more great hardware writeups check out a general hardware build for a single sensing node, or the “temperature sensor” [Edward] made with no external parts at all!

Banana Bomb Is Likely To Get You In Trouble

If there’s one thing Hollywood loves, it’s a ticking clock to create drama. Nuclear weapons, terrorist bombs, and all manner of other devices have been seen featuring foreboding numbers counting down on a series of 7-segment displays. In this vein, [deshipu] developed a rather ridiculous take on the classic trope.

The project is built around a ticking four-digit display. The blue LEDs give it a modern touch, and it’s attached on top of an Arduino Pro Mini 3.3V. This enables the whole module to be powered by a coin cell, for an incredibly compact and tidy timer that is barely bigger than the display itself. There’s also a buzzer attached, which chirps each second, somewhat heightening the stress level in the immediate vicinity.

With a functioning timer, [deshipu] then went for comedy points, by hooking it up to a trio of bananas. This is widely considered more courteous than attaching it to a detonator circuit and actual dynamite, and is key to staying off government watchlists.

It’s a piece that would be amusing at a Halloween party or similar, and is easily completed by any beginner learning Arduino. It goes without saying that, while this is amusing, it’s a build that should very much not be bandied about in public or used for a prank. In this day and age, even touting a custom clock can draw unwelcome attention, so it’s important to be careful.  Video after the break.

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Build A Sprint Race Timer To Help Your Training

Any exercise is a positive thing, but if you’re looking to improve over time, you’ve got to measure your performance. [Nikodem Bartnik] is a runner and is looking to improve his sprinting abilities. Naturally, an Arduino is the perfect companion to help in this quest (YouTube link, embedded below).

The Arduino is built into a 3D printed enclosure, with several buttons for input. Rather unconventionally, a small e-paper display was chosen for the interface. This has the benefits of being easily readable outdoors during the day, as well as using very little power.

The device is simple to use, and makes training alone a breeze. The distance to be run can be selected, and the unit emits a series of beeps to indicate to the runner when to begin. The timer is placed at the finish line, and detects the runner passing by with an ultrasonic sensor.

It’s a useful build for sprint timing, and could be made even more versatile with a remote start function. If you need to time Hot Wheels instead of sprinters, don’t worry – there’s a build for you too. Video after the break.

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The Surprising Tech Of A Cheap Toaster

How complicated can a toaster be? You can get a cheap one for way under $10 that is little more than a hot wire. However, there are a few little complications. First, consumer products need to be safe — lawsuits are expensive. Second, there has to be some mechanism to hold the toast down until it is done. If you can buy one for $10 you can bet it isn’t some super toast processor running Linux in there.

[Technology Connections] tore one down for you so you don’t have to. The circuitry is simple, and who knew there was a dedicated IC for toaster control? However, the real engineering is in the lowly little handle you pull down to start the toasting.

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A Perfectly Orderly Way To Manage Your Time

[Paul Gallagher] has spent years separating his tasks into carefully measured out blocks, a method of time management known as the Pomodoro Technique. If that’s not enough proof that he’s considerably more organized and structured than the average hacker, you only need to take a look at this gorgeous Pomodoro Timer he’s entered into the Circuit Sculpture Contest. Just don’t be surprised if you suddenly feel like your own time management skills aren’t cutting it.

While [Paul] has traditionally just kept mental note of the hour-long blocks of time he breaks his work into, he thought it was about time he put together a dedicated timer to make sure he’s running on schedule. Of course he could have used a commercially available timer or an application on his phone, but he wanted to make something that was simple and didn’t cause any distractions. A timer that was easy to start, reliable, and didn’t do anything extraneous. We’re not sure if looking like the product of a more advanced civilization was part of his official list of goals, but he managed to achieve it in any event.

The timer is broken up into two principle parts: the lower section which has the controls, USB port, a handful of passive components, and an ATmega328 microcontroller, and the top section which makes up the three digit LED display. The two sections are connected by a header on the rear side which makes it easy for [Paul] to take the timer apart if he needs to get back into it for any reason. Notably absent in the design is a RTC; the relatively short duration of the timer (up to a maximum of 95 minutes) means the ATmega328 can be trusted to keep track of the elapsed time itself with an acceptable amount of drift.

The display side of the timer is really a sight to behold, with the legs of each LED soldered to a pair of carefully bent copper wires so they match the angle of the front panel. The associated resistors have been artfully snipped so that their bodies sit flat on the PCB while their leads reach out to the perfect length. It looks like a maintenance nightmare in there, but we love it anyway.

As we near the half-way mark of the Circuit Sculpture Contest, there’s still plenty of time to submit your own piece of functional art. If you’ve got a project that eschews the printed circuit board for a chance to bare it all, write it up on Hackaday.io and be sure to send it in before the January 8th, 2019 deadline.

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The 555 And How It Got That Way

There’s a certain minimum set of stuff the typical Hackaday reader is likely to have within arm’s reach any time he or she is in the shop. Soldering station? Probably. Oscilloscope? Maybe. Multimeter? Quite likely. But there’s one thing so basic, something without which countless numbers of projects would be much more difficult to complete, that a shop without one or a dozen copies is almost unthinkable. It’s the humble 555 timer chip, a tiny chunk of black plastic with eight leads that in concert with just a few extra components can do everything from flashing an LED a couple of times a second to creating music and sound effects.

We’ve taken a look under the hood of the 555 before and featured many, many projects that show off the venerable chip’s multiple personalities quite well. But we haven’t looked at how Everyone’s First Chip came into being, and what inspired its design. Here’s the story of the 555 and how it got that way.

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Minimal Blinky Project Makes The Chip The Circuit Board

We’ve got a thing for projects that have no real practical value but instead seek to answer a simple yet fundamental question: I wonder if I can do that? This dead-bug style 555 blinky light is one of those projects, undertaken just to see how small a circuit can be. Pretty small, as it turns out, and we bet it can get even smaller.

[Danko]’s minimal circuit is about as small as possible for the DIP version of the venerable 555 chip. The BOM is stripped to the bone: just the chip, three resistors, a capacitor, and an LED. All the discrete components are SMDs in 0805. The chip’s leads are bent around the package to form connections, and the SMDs bridge those “traces” to complete the circuit. [Danko] shows the build in step-by-step detail in the video below. There’s some fairly fine work here, but we can’t help wondering just how far down the scale this could be pushed. We know someone’s made a smaller blinky using a tiny microcontroller, but we’d love to see this tried with the BGA version of the chip which is only 1.4 mm on a side.

Cheers to [Danko] for trying this out and having some fun with an old chip. He seems to have a bit of a thing for the 555; check out this cute robot sculpture that’s built around the chip.

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