How HP Calculators Communicate Over Infrared

January 27, 2026 by Lewin Day 10 Comments

For most people, calculators are cheap and simple devices used for little more than addition and the odd multiplication job. However, when you get into scientific and graphical calculators, the feature sets get a lot more interesting. For example, [Ready? Z80] has this excellent explainer on how HP’s older calculators handle infrared communications.

The video focuses on the HP 27S Scientific Calculator, which [Ready? Z80] found in an op-shop for just $5. Introduced in 1988, the HP-27S had the ability to dump screen data over an infrared link to a thermal printer to produce paper records of mundane high-school calculations or important engineering math. In the video, [Ready? Z80] explains the communication method with the aid of Hewlett-Packard’s own journal publication from October 1987, which lays out of the details of “the REDEYE Protocol.” Edgy stuff. It’s pretty straightforward to understand, with the calculator sending out bursts of data in six to eight pulses at a time, modulated onto a 32.768KHz square wave as is the norm. [Ready? Z80] then goes a step further, whipping up custom hardware to receive the signal and display the resulting data on a serial terminal. This is achieved with a TEC-1G single-board computer, based on the Z80 CPU, because that’s how [Ready? Z80] does things.

We’ve seen other great stuff from this channel before, too. For example, if you’ve ever wanted to multitask on the Z80, it’s entirely possible with the right techniques. Video after the break.

Continue reading “How HP Calculators Communicate Over Infrared” →

The host stands in his electronics lab with the image of four remote controls overlaid.

Introducing Infrared Remote Control Protocols

April 13, 2025 by John Elliot V 23 Comments

Over on his YouTube channel [Electronic Wizard] has released a video that explains how infrared (IR) remote controllers work: IR Remote Controllers protocol: 101 to advanced.

This video covers the NEC family of protocols, which are widely used in typical consumer IR remote control devices, and explains how the 38 kHz carrier wave is used to encode a binary signal. [Electronic Wizard] uses his Rigol DS1102 oscilloscope and a breadboard jig to sniff the signal from an example IR controller.

There is also an honorable mention of the HS0038 integrated-circuit which can interpret the light waves and output a digital signal. Of course if you’re a tough guy you don’t need no stinkin’ integrated-circuit IR receiver implementation because you can build your own!

Before the video concludes there is a brief discussion about how to interpret the binary signal using a combination of long and short pulses. If this looks similar to Morse Code to you that’s because it is similar to Morse Code! But not entirely the same, as you will learn if you watch the video!

Small Mammals Appear To Have A Secret Infrared Sense

July 22, 2024 by Lewin Day 21 Comments

If you’ve ever watched Predator, you’ve noted the tactical advantage granted to the alien warrior by its heat vision. Indeed, even with otherwise solid camoflauge, Dutch and his squad ended up very much the hunted.

And yet, back in reality, it seems the prey might be the one with the ability to sense in the infrared spectrum. Research has now revealed this unique ability may all be down to the hairs on the back of some of the smallest mammals.

Continue reading “Small Mammals Appear To Have A Secret Infrared Sense” →

Tokyo Atacama Observatory Opens As World’s Highest Altitude Infrared Telescope

May 6, 2024 by Maya Posch 5 Comments

Although we have a gaggle of space telescopes floating around these days, there is still a lot of value in ground-based telescopes. These generally operate in the visible light spectrum, but infrared ground-based telescopes can also work on Earth, assuming that you put them somewhere high in an area where the atmosphere is short on infrared-radiation absorbing moisture. The newly opened Universe of Tokyo Atacama Observatory (TAO) with its 6.5 meter silver-coated primary mirror is therefore placed on the summit of Cerro Chajnantor at 5,640 meters, in the Atacama desert in Chile.

This puts it only a few kilometers away from the Atacama Large Millimeter Array (ALMA), but at a higher altitude by about 580 meters. As noted on the University of Tokyo project site (in Japanese), the project began in 1998, with a miniTAO 1 meter mirror version being constructed in 2009 to provide data for the 6.5 meter version. TAO features two instruments (SWIMS and MIMIZUKU), each with a specific mission profile, but both focused on deciphering the clues about the Universe’s early history, a task for which infrared is significantly more suitable due to redshift.

Infrared Following Robot Built As Proof-of-Concept For Autonomous Luggage

December 23, 2023 by Lewin Day 7 Comments

Once upon a time, the poor humans of the past had to lug around suitcases and trunks with their own arms. Then, some genius figured out that you could just put wheels on and make everyone’s life a million times easier. Now, what if you didn’t even have push, because your luggage could just follow you instead? Well, students [Yuqiang Ge] and [Yiyang Zhao] have figured out a proof of concept for how that could work.

Their build is a small robotic platform that they assembled for their ECE5730 final project. The tiny wheeled robot is programmed to rotate on the spot until its infrared sensors pick up a signal. In turn, the user is intended to carry an infared beacon for it to lock onto. A pair of sensors are used on the robot platform, separated by a board to serve as a blind. The robot determines the relative signal strength from each sensor, and uses that to vary PWM signals to the two DC drive motors to steer the robot platform to seek and follow the infrared beacon.

It’s a neat idea, and looks to work pretty well in a university corridor. It even has an ultrasonic range sensor to (ideally) stop when it gets too close to the user. Whether it would survive the tumult of a crowded airport is another thing entirely, but that’s what the engineering process is about. Indeed, the very concept has been commercialized already!

Following-robots are a common student project, and one well worth exploring if you’re new to the robotic field.

Continue reading “Infrared Following Robot Built As Proof-of-Concept For Autonomous Luggage” →

A display in a field showing the water stress index over time

Hackaday Prize 2022: Using Infrared Thermometers To Measure Crops’ Water Stress

September 11, 2022 by Robin Kearey 6 Comments

If you live anywhere on the Northern Hemisphere, you’re likely to have experienced one of the many heatwaves that occurred this summer. Extreme heat is dangerous for humans and animals, but plants, including important crops, also suffer. High temperatures lead to increased transpiration and evaporation, and if the water lost in this way is not replenished quickly enough, plants will stop growing and eventually wither and die.

In order to keep track of the amount of water available to crops, [Florian Ellsäßer] built the Crop Water Stress Sensor: a device that checks whether plants have enough moisture available to stay healthy. It does this by measuring the temperature of the leaves to calculate evaporation levels. If the leaves are cooler than their surroundings, this means that water is evaporating from them and the plant apparently has enough water available. If the leaves’ temperature is closer to the ambient temperature, then the plant may be running low on water.

[Florian]’s system performs this measurement using an infrared array, which is basically a low-resolution thermal camera that remotely measures the temperature of everything in its field of view. This IR array is pointed at a field, where it will see both leaves and the ground between them. The difference in temperature between these two can then be used to calculate the Crop Water Stress Index (CWSI), a standardized measure of how well-hydrated plants are. The result is shown on a display and also indicated using a convenient red-yellow-green status LED that shows if the crops in question need watering.

The system can be solar powered for completely remote operation, while its data can be read out through a WiFi interface. [Florian] is planning to update the design with a LoRa interface for greater range: the eventual goal is to build a large network of these sensors throughout agricultural areas and use the combined data to raise awareness of water shortages in certain areas. In order to make the sensors easy to build by anyone interested, all design files are available on the project page.

Keeping crops moisturized is one of the key tasks of agriculture, and we’ve seen several projects that aim to optimize and automate it, from a simple-but-effective ESP8266-based moisture sensor to complete hydroponics systems.

3D Printing Goes Near Infrared

February 3, 2022 by Al Williams 17 Comments

Researchers at the University of Texas have been experimenting with optical 3D printing using near infrared (NIR) light instead of the more traditional ultraviolet. They claim to have a proof of concept and, apparently, using NIR has many advantages. The actual paper is paywalled, but there are several good summaries, including one from [3D Printing Industry].

UV light degrades certain materials and easily scatters in some media. However, decreasing the wavelength of light used in 3D printing has its own problems, notably less resolution and slower curing speed. To combat this, the researchers used an NIR-absorbant cyanine dye that exhibits rapid photocuring. The team reports times of 60 seconds per layer and resolution as high as 300 micrometers. Nanoparticles in the resin allow tuning of the part’s appearance and properties.

Continue reading “3D Printing Goes Near Infrared” →