Monthly Archives: April 2019

App note: Reduced power dissipation of relay loads

via Dangerous Prototypes

an_on_AND9797-D

Another app note from ON Semiconductors on using PWM technique to reduce power consumed when latching mechanical relays. Link here (PDF)

Integrated circuit driver circuits often use relay loads in their application. Output drivers are a source of power dissipation on the IC. Latching relays can be used to keep sustaining load current at a minimum by engaging and removing drive current, but a PWM system can also preserve reduced power conditions by engaging and reducing duty cycle using standard type relays.

By considering the Maximum Turn−On Voltage and Minimum Turn−Off Voltage specifications typically quoted in the relay electrical specification, your system design can utilize a signal to pull−in and activate the relay followed by a reduced power PWM sustaining signal.

App note: The load switch – Selection and use of ecoSWITCH(TM) products

via Dangerous Prototypes

an_on_and9848-d

ecoSWITCH(TM) from ON Semiconductors offers space saving solution on power distribution system. Link here (PDF)

Load switches play an important part in the management of supply domains and the protection of the loads they supply. Loads switches are often used for power sequencing, standby load leakage reduction, and inrush current control. Integrated ecoSWITCH products deliver an area reducing solution, offering over current protection, load soft start, and extremely low on series resistances of sub − 20 milliohm. This article discusses the primary benefits of load switches, application considerations, and how ecoSWITCH differs from other types of integrated switch offerings. A generic cloud system application and USB power delivery example are presented to demonstrate how the addition of ecoSWITCH solves design challenges such as achieving low quiescent current, local load protection, and startup sequencing.

New product: DB15 Screw Terminal Adapter for MCP23X/26X Advanced Motor Controllers

via Pololu Blog

DB15 Screw Terminal Adapter for MCP23X/26X Advanced Motor Controllers with included hardware.

DB15 screw terminal adapter mated to an MCP266 Advanced Motor Controller.

We are now carrying a DB15 Screw Terminal Adapter for MCP23X/26X Advanced Motor Controllers. The adapter breaks out connections from the DB15 connector to a set of screw terminals, making accessing those pins easier during prototyping. It is designed specifically to work with the MCP Advanced Motor Controllers that feature a DB15 connector: the MCP233, MCP236, MCP263, and MCP266. However, it could also be used as a generic breakout board for other hardware that uses the same connector, like old computer joysticks or MIDI devices (where it is called a game port).

Rudimentary ultrasound machine made with Arduino Due

via Arduino Blog

Ultrasound images are an important tool for medical diagnosis, and while units used by doctors can be very expensive, getting a basic image doesn’t have to be. Inspired by this attempt at a $500 ultrasound machine seen here, maker “stoppi71” decided to create his own using a 5 MHz ultrasound transducer via a paint-thickness gauge.

An Arduino Due provides computing power to turn sound pulses into images, while a 3.5-inch TFT display shows what it’s examining. Short pulses in the 100-200 nanosecond range are generated with the help of a monoflop and MOSFET, returning an echo corresponding to what it’s “looking” at. 

Although the results are not nearly what you’d expect at the doctor’s office, rudimentary readings of skin and bone are definitely visible. 

I’ve examined different objects from aluminum-cylinders over water-filled balloons to my body. To see body-echos the amplification of the signals must be very high. For the aluminum-cylinders a lower amplification is needed. When you look at the pictures you can clearly see the echoes from the skin and my bone.

So what can I say about the success or failure of this project. It is possible to look inside the body with such simple methods and using parts, which aren’t commonly intended for that purpose. But these factors are limiting the results too. You don’t get such clear and well structured pictures compared with commercial solutions.

Friday Product Post: You’ve Been Thunderstruck!

via SparkFun: Commerce Blog

Hello, there everyone! It's Friday, and that means we have some new products to show you all - starting with a Lightning Detector Breakout. Yup, you read that right! We also have the new Google Coral Single Board Computer, and three DMX cables. Let's take a closer look at all!

Storm's Coming, Ani!

SparkFun Lightning Detector - AS3935 (Qwiic)

SparkFun Lightning Detector - AS3935 (Qwiic)

SEN-15276
$24.95

Add the SparkFun Qwiic Lightning Detector to your next weather station to make sure you are aware of any potential hazardous weather heading your way. The AS3935 is capable of detecting lightning up to 40 km away, with an accuracy of 1 km to the storm front, and a sensitive antenna tuned to pick up lightning events in the 500 kHz band. Utilizing our handy Qwiic system, no soldering is required to connect it to the rest of your system. However, we still have broken out 0.1"-spaced pins in case you prefer to use a breadboard.


Google Coral Development Board

Google Coral Development Board

DEV-15318
$156.95

The Coral Dev Board is a single-board computer with a removable system-on-module (SOM) that contains eMMC, SOC, wireless radios and the Edge TPU. You can use the Dev Board as a single-board computer when you need accelerated ML processing in a small form factor, but it also serves as an evaluation kit for the SOM. You can use the dev board to prototype internet-of-things (IoT) devices and other embedded systems that demand fast on-device ML inferencing, and then scale to production using just the 40 mm × 48 mm SOM board combined with your custom PCB hardware using board-to-board connectors.


XLR-3 (DMX) Cable - 5ft

XLR-3 (DMX) Cable - 5ft

CAB-15308
$4.95

This is a five-foot-long (~1.5 m) DMX cable capable of better communications for lighting and special effects through standard or digital communication protocols. We specifically like to use this cable with our ESP32 Thing Plus DMX to LED Shield, but it can also be used to interface with other DMX fixtures, as well!

If you need a longer cable, you're in luck! We also offer cable lengths of 10 ft and 25 ft.


That's it for this week! As always, we can't wait to see what you make! Shoot us a tweet @sparkfun, or let us know on Instagram or Facebook. We’d love to see what projects you’ve made!

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Avalanche Noise Generator Notes

via Hacking – bunnie's blog

Good sources of entropy (noise) are an essential part of modern cryptographic systems. I designed a mobile-friendly avalanche noise generator as part of the background work I’ve been doing for the betrusted project (more on that project later). I had to do a new design because the existing open-source ones I could find were too large and power hungry to integrate into a mobile device. I also found it hard to find solid theory pieces on avalanche noise generators, so in the process of researching this I wrote up all my notes in case someone needs to do a ground-up redesign of the system again in the future.

Here’s an excerpt from the notes:

Avalanche breakdown is essentially a miniature particle accelerator, where electrons that enter a PN junction’s depletion region (through mechanisms that include thermal noise) are accelerated across an electrical field, to the point where new electron-hole pairs are generated when these high-energy electrons collide with atoms in the depletion region, creating an amplification cascade with low reproducibility.

An approximate analogy is an inflatable pool filled with water. The height of the pool is the potential barrier of the reverse-biased PN junction. A hose feeding water into the pool represents a constant current of electrons. The volume of the pool can be thought of as the depletion capacitance, that is, the capacitor created by the region of the junction that is void of carriers due to natural drift and diffusion effects. As water trickles into the pool, the water level rises and eventually forms a meniscus. Random disturbances, such as ripples on the surface due to wind, eventually cause the meniscus to crest over the edge of the pool. The water flowing over the edge pushes down on the inflatable pool’s side, causing more water to flow, until the level has reduced to a point where the inflatable pool’s side can snap back into its original shape, thus restarting the cycle of filling, cresting, and breakdown. The unpredictability of when and where the breakdown might happen, and how much water flows out during the event, is analogous to the entropy generated by the avalanche effect in a PN junction.

The electrical characteristic of avalanche noise biased by a constant current source is a “sawtooth” waveform: a linear ramp up in voltage as the capacitance of the depletion region charges to the point where the electric field becomes large enough to initiate the cascade, and then a sharp drop off in voltage as the cascade rapidly discharges the junction capacitance. The cascade then abruptly halts once the field is no longer strong enough to sustain the cascade effect, leading to a subsequent cycle of charging and breakdown.

The site also includes detailed schematics and measurement results, such as this one.

The final optimized design takes <1cm^2 area and draws 520uA at 3.3V when active and 12uA in standby (mostly 1.8V LDO leakage for the output stage, included in the measurement but normally provided by the system), and it passes preliminary functional tests from 2.8-4.4V and 0-80C. The output levels target a 0-1V swing, meant to be sampled using an on-chip ADC from a companion MCU, but one could add a comparator and turn it into a digital-compatible bitstream I suppose. I opted to use an actual diode instead of a NPN B-E junction, because the noise quality is empirically better and anecdotes on the Internet claim the NPN B-E junctions fail over time when operated as noise sources. I’ll probably go through another iteration of tweaking before final integration, but afaik this is the smallest, lowest power open-source avalanche noise generator to date.