No DAC? Try PDM

January 6, 2024 by Al Williams 16 Comments

Ever notice that the ESP32-S3 doesn’t have a digital-to-analog converter? [Chris] did and asserts that he doesn’t care because he can just use the PDM system to get the same result. PDM — pulse density modulation — is similar to PWM and, like PWM, requires a filter that could range from a simple RC network to an active filter. You can see the result in the video below.

There are several ways [Chris] could produce the output he wanted. PWM was one choice, and some example code uses a timer to do PDM. However, that is not very efficient. The other alternative is to use the I2S output. However, this does require a few workarounds.

In particular, the I2S output is always stereo and incorporates a clock output that isn’t needed for this application. [Chris] simply output the same value on both channels and routed the clock to some pins that are normally used for startup options. That means they can’t easily be used for your own inputs, but it’s OK to use them for unimportant outputs.

We always enjoy seeing solutions like this because it can give you ideas for use in your own projects. Of course, this won’t apply to every project where you need a DAC, but it still might give you some ideas.

We have looked at PDM before. You could, too, build your own DAC hardware.

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Telescope Rides On 3D Printed Equatorial Table

January 4, 2024 by Bryan Cockfield 25 Comments

In the realm of amateur astronomy, enthusiasts find themselves navigating a cosmos in perpetual motion. Planets revolve around stars, which, in turn, orbit within galaxies. But the axial rotation of the Earth and the fact that its axis is tilted is the thing that tends to get in the way of viewing celestial bodies for any appreciable amount of time.

Amateur astronomy is filled with solutions to problems like these that don’t cost an arm and a leg, though, like this 3D printed equatorial table built by [aeropic]. An equatorial table is a device used to compensate for the Earth’s rotation, enabling telescopes to track celestial objects accurately. It aligns with the Earth’s axis, allowing the telescope to follow the apparent motion of stars and planets across the night sky.

Equatorial tables are specific to a location on the Earth, though, so [aeropic] designed this one to be usable for anyone between around 30° and 50° latitude. An OpenSCAD script generates the parts that are latitude-specific, which can then be 3D printed.

From there, the table is assembled, mounted on ball bearings, and powered by a small stepper motor controlled by an ESP32. The microcontroller allows a telescope, in this case a Newtonian SkyWatcher telescope, to track objects in the sky over long periods of time without any expensive commercially-available mounting systems.

Equatorial tables like these are indispensable for a number of reasons, such as long-exposure astrophotography, time lapse imaging, gathering a large amount of observational detail for scientific purposes, or simply as an educational tool to allow more viewing of objects in the sky and less fussing with the telescope. They’re also comparatively low-cost which is a major key in a hobby whose costs can get high quickly, but not even the telescope needs to be that expensive. A Dobsonian telescope can be put together fairly quickly sometimes using off-the-shelf parts from IKEA.

Current-Based Side-Channel Attacks, Two Ways

January 4, 2024 by Dan Maloney 9 Comments

Funny things can happen when a security researcher and an electronics engineer specializing in high-speed circuits get together. At least they did when [Limpkin] met [Roman], which resulted in two interesting hardware solutions for side-channel attacks.

As [Limpkin] relates it, the tale began when he shared an office with [Roman Korkikian], a security researcher looking into current-based attacks on the crypto engine inside ESP32s. The idea goes that by monitoring the current consumption of the processor during cryptographic operations, you can derive enough data to figure out how it works. It’s difficult to tease a useful signal from the noise, though, and [Roman]’s setup with long wire runs and a noisy current probe wasn’t helping at all. So [Limpkin] decided to pitch in.

The first board he designed was based on a balun, which he used to isolate the device under test from the amplification stage. He found a 1:8 balun, normally used to match impedances in RF circuits, and used its primary as a shunt resistance between the power supply — a CR1220 coin cell — and the DUT. The amplifier stage is a pair of low-noise RF amps; a variable attenuator was added between the amp stages on a second version of the board.

Board number two took a different tack; rather than use a balun, [Limpkin] chose a simple shunt resistor with a few twists. To measure the low-current signal on top of the ESP32’s baseline draw would require such a large shunt resistor that the microcontroller wouldn’t even boot, so he instead used an OPA855 wideband low-noise op-amp as an amplified shunt. The output of that stage goes through the same variable attenuator as the first board, and then to another OPA855 gain stage. The board is entirely battery-powered, relying on nice, quiet 18650s to power both the DUT and the shunt.

How well does it work? We’ll let you watch the talk below and make up your own mind, but since they’ve used these simple circuits to break a range of different chips, we’d say this approach a winner.

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Open Source DC UPS Keeps The Low-Voltage Gear Going

December 22, 2023 by Dan Maloney 26 Comments

We all like to keep our network gear running during a power outage — trouble is, your standard consumer-grade uninterruptible power supply (UPS) tends to be overkill for routers and such. Their outlet strips built quickly get crowded with wall-warts, and why bother converting from DC to AC only to convert back again?

This common conundrum is the inspiration for [Walker]’s DC UPS design, which has some interesting features. First off, the design is open source, which of course invites tinkering and repurposing. The UPS is built for a 12 volt supply and load, but that obviously can be changed to suit your needs. The battery bank is a 4S3P design using 18650 cells, and that could be customized as well. There’s an ideal diode controller that prevents DC from back-feeding into the supply when the lights go out, and a really interesting synchronous buck-boost converter in place of the power management chip you’d normally see in a UPS. The converter chip takes a PWM signal from an RP2040; there’s also an ESP32 onboard for web server and UI duties as well as an STM32 to run the BMS. The video below discusses the design and shows a little of the build.

We’ve seen a spate of DC UPS designs lately, some more elaborate than others. This one has quite a few interesting chips that most of us don’t normally deal with, and it’s nice to see how they’re used in a practical design.

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Bed Sensors Do More Than You’d Think

December 21, 2023 by Kristina Panos 24 Comments

Bed sensors do sort of sound like a gimmick — after all, who cares whether someone is occupying the bed? But if you think about it, that information is quite useful from a home automation standpoint. A person could do all sorts of things in this state, from ensuring the overhead lights in the room can’t come on, to turning off other smart devices that are likely not being used while both occupants are sleeping.

[The Home Automation Guy] presents a couple of ways of doing this, but both center around a fairly inexpensive pressure-sensing mat.

In the first method, he connects the pressure mat up to a Zigbee Aqara Leak Sensor, which conveniently has two terminals on the back to accept the wires from the pressure sensor. Then he simply connects it up to a Zigbee-compatible home assistant like the Aqara Hub.

In slightly harder mode, he forgoes the Aqara Leak Sensor and connects the pressure mat up to an ESP32 using a nifty screw terminal dev board. Then he sets up the sensor and all the desired actions in ESPHome. Of course, with an ESP32, it’s easy to add a second pressure mat for [Mrs. The Home Automation Guy]’s side of the bed.

Now, once they’ve both gone off to bed, the house goes into night mode — all the smart plugs, Sonos devices, and other things are powered down, and the alarm system is put into night mode. Be sure to check out the build video after the break.

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Take The Minimal Pain Out Of ESP32 Programming

December 15, 2023 by Jenny List 29 Comments

Perhaps without many of us realising it, our single board computers perform the task of making programming their processor or SoC a lot easier. They take care of setting the right lines or commands to put the chip in programming mode, they deal with timings, such that we simply fire our code from our dev environment without having to expend much thought. It’s not as though it’s difficult to program most microcontrollers, but there is usually a procedure to set the chip in programming mode. Tired of pressing buttons to achieve this with the ESP32, [DoganM95] took the time to create an all-in-one USB ESP32 programming board.

It’s a straightforward enough CH340C design that also has a USBC-PD chip on-board allowing powering of an attached ESP32 from PD sources. It’s all the stuff you’d find incorporated on a little dev board, without the ESP32, so while it’s nothing earth-shattering it’s also a neat and useful little addition to your arsenal. Unsurprisingly it’s not the first time someone’s created a similar board for a commercially available ESP32 module.

Bluetooth As Proxy For Occupancy

December 13, 2023 by Bryan Cockfield 59 Comments

During [Matt]’s first year of college, he found in a roundabout way that he could avoid crowds in the dining hall by accessing publicly available occupancy data that the dining hall collected. Presumably this was data for the dining hall to use internally, but with the right API calls anyone could use the information to figure out the best times to eat. But when the dining hall switched providers, this information feed disappeared. Instead of resigning himself to live in a world without real-time data on the state of the dining hall, he recreated the way the original provider counted occupancy: by using Bluetooth as a proxy for occupancy.

Bluetooth devices like smartphones, fitness sensors, and other peripherals often send out advertising packets into the aether, to alert other devices to their presence and help initiate connections between devices. By sniffing these advertising packets, it’s possible to get a rough estimate of the number of people in one particular place, assuming most people in the area will be carrying a smartphone or something of that nature. [Matt]’s Bluetooth-sniffing device is based on the ESP32 set up to simply count the number of unique devices it finds. He had some trouble with large crowds, though, as the first ESP32 device he chose didn’t have enough RAM to store more than a few hundred IDs and would crash once the memory filled. Switching to a more robust module seems to have solved that issue, and with a few rounds of testing he has a workable prototype that can run for long periods and log at least as many Bluetooth devices passing by as there are within its range.

While [Matt] hasn’t deployed this to the dining hall yet, with this framework in place most of the work has been done that, at least in theory, one of these modules could be easily placed anywhere someone was interested in collecting occupancy data. He has plans to submit his project to the university, to research the topic further, and potentially sell these to businesses interested in that kind of data. This isn’t an idea limited to the ESP32, either. We’ve seen similar projects built using the Raspberry Pi’s wireless capabilities that perform similar tasks as this one.

Thanks to [Adrian] for the tip!