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Contactless transit card teardown

Posted on Monday, July 25th, 2016 in RFID, Teardowns by DP | No Comments

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A RFID transit pass teardown from Electronupdate:

Here is the die photo: super tiny. I bet they get thousands of dice off of each wafer. Looks like it’s a protocol called MIFARE. Vendor of the chips is NXP. I think it’s their ultra light family
The amazing bit is that a card is printed with conductive ink, a semiconductor added (with a transistor count in the tens of thousands), a vendor-specific ID placed on the outside with another layer of paper, spooled in to giant rolls, vended for a single trip and then thrown away…..

More details at Electronupdate blog.

Check out the video after the break.  (more…)

Homebrew Raspberry pi shutdown button

Posted on Monday, July 25th, 2016 in DIY, R-Pi by DP | No Comments

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Facelesstech made his own Raspberry pi shutdown button and wrote a post on his blog detailing its assembly:

One thing I learn from my last shut down button was that the raspberry pi has internal pull up resistors so I didn’t need a 10k and a 1k pull up resistor on this design. This would save me a lot of space and pins on the new revision.
The reason I have decided to use these pins is that it doesn’t block any important pins you might be wanting to use during prototype of your project. All the other shut down buttons cover over the pins at the top of the header which include the SPI pins and most of the power pins. I have to admit mine doesn’t seam to be a bit more difficult to place in the correct place but I think that its a small price to pay for not having the important pins covered.

More details at Facelesstech blog.

Free PCB Sunday: Pick your PCB

Posted on Sunday, July 24th, 2016 in Free PCBs by DP | 29 Comments

IRToy

We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

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App note: Flow sensing in tankless water heaters

Posted on Sunday, July 24th, 2016 in app notes by DP | No Comments

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Contactless reed switches from Littelfuse provides flow and water presence monitoring. Link here (PDF)

Reed switches and sensors are highly effective solutions for flow sensing applications that can be used for detecting the presence of fluid flow in a system or even measure the rate of fluid flow.

Tankless water heaters are becoming a widely popular solution for water heating needs. The availability of hot water on demand and the perceived limitless supply of hot water make these types of water heaters much more attractive than traditional tank water heaters. These water heaters also provide long-term energy savings since energy is used only when there is a demand for hot water. In order to effectively heat the water when there is a demand, a sensor is needed to detect the flow of water.

App note: Circuit protection technology application matrix application guide

Posted on Sunday, July 24th, 2016 in app notes by DP | No Comments

Here’s an application matrix of Littelfuse’s circuit protections, Link here (PDF)

App note: Creating a custom flash-based bootstrap loader (BSL)

Posted on Sunday, July 24th, 2016 in app notes by DP | No Comments

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An application note (PDF!) from TI on creating a custom flash-based bootstrap loader (BSL):

MSP430F5xx and MSP430F6xx devices have the ability to locate their bootstrap loader (BSL) in a protected location of flash memory. Although all devices ship with a standard TI BSL, this can be erased,and a custom made BSL can be programmed in its place. This allows for the creation of using custom communication interfaces, startup sequences, and other possibilities. It is the goal of this document to describe the basics of the BSL memory, as well as describe the TI standard BSL software so it may be reused in custom projects.
This application report also includes a small demonstration BSL that can be used on MSP430G2xx devices. An entry sequence starts the code update and allows the new user code to be sent and stored in flash. A one-byte feedback is provided to indicate status. TA0-based UART communication is used for entry sequence, data, and feedback.

Inverter crystal oscillator

Posted on Saturday, July 23rd, 2016 in techniques by DP | 1 Comment

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Vasily Ivanenko writes:

In numerous RF synthesizer chips lies an inverter with input and output pins for making a reference crystal oscillator clock. I built some discrete chip inverter xtal oscillators with 74HC series logic gates to better examine them. You’ll quickly recognize the oft-used Pierce oscillator topology with 1 trimmer capacitor to tweak the fundamental frequency which might vary from factors like crystal aging and gate, crystal, crystal holder + board reactances.
I determined the 27 pF and trimmer cap values through experiments and measures.

More details at QRP HomeBuilder blog.

Free PCB coupon via Facebook to 2 random commenters

Posted on Friday, July 22nd, 2016 in Free PCBs by DP | 2 Comments

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Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. The coupon code usually go to Facebook ‘Other’ Messages Folder . More PCBs via Twitter on Tuesday and the blog every Sunday. Don’t forget there’s free PCBs three times every week:

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Tote – Quadruped robot

Posted on Friday, July 22nd, 2016 in DirtyPCBs.com, robotics by DP | 1 Comment

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Radomir Dopieralski has a nice build log on his quadruped robot – Tote:

Tote is a small (fits inside your palm), four-legged, walking robot, with three degrees of freedom per leg, Arduino for its brains and controlled either with a TV remote, or by additional electronics added on top of it. It is very simple, cheap and sturdy, for this class of robots. Its goal is to be a starting point for anyone who wants to start building multi-legged robots.

Check out the video after the break.
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TV Tuner IR remote with a PIC16F684

Posted on Friday, July 22nd, 2016 in infrared, PIC by DP | 1 Comment

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Tahmid built a TV tuner IR remote with a PIC16F684:

I then proceeded to write an IR transmitter using the PIC16F684 (using the MPLAB X IDE and XC8 compiler), following the timing information from the extended NEC protocol. In order to connect all the keys, I connected them in matrix keypad form.
In order to power the remote off 2xAA batteries, it is necessary to use sleep mode – otherwise the battery will be drained extremely quickly. So, in order to detect when a button is pressed, an interrupt is used. After the IR command is sent, the microcontroller goes to sleep. The interrupt wakes up the microcontroller when a button is pressed. Debouncing is achieved using simple software delays. When a button is held down, the NEC command repeat sequence is not sent. Instead, the remote relies on releasing the button and pressing it again.

More details at Tahmid’s blog.

Homebrew Multimode Digital Voice Modem (MMDVM) adapter

Posted on Thursday, July 21st, 2016 in DIY by DP | 1 Comment

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Florian Wolters made his own version of MMDVM adapter:

During experiments with digital voice mode in hamradio I discovered a nice project describing an adapter for D-Star, DMR and other digital modes based on an Arduino Due and a little PCB to be put on top. This unit is called the Multimode Digital Voice Modem or MMDVM (see [1]). It seems that this is getting quite popular because hard- and software is Open Source.

Check out the video after the break. (more…)

ESP8266 temperature logger

Posted on Thursday, July 21st, 2016 in wireless by DP | No Comments

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A ESP8266 temperature logger project from Facelesstech:

I decided to use the esp-01 module because I only need 2 GPIO pins since I was using the DS18B20 temp sensor and the WS2812 LED. This made the hardware really cheap and easy to reproduce too. I normally use FTDI boards when it comes to the USB to serial on my projects but I couldn’t find a FTDI board with micro USB that didn’t cost the earth. That’s why I went with the CP2102 which I hadn’t used before.
I think what really made me feel good about this project was the fact that I came up with the idea to use a Full sided male USB port for power teamed with a AMS1117 3.3v voltage regulator. This would allow me to just plug this straight into a USB wall wart or a phone charger battery bank.

More details at Facelesstech site.  All project files and code are available on Github.

Check out the video after the break. (more…)

9V/1kV DC/DC converter

Posted on Wednesday, July 20th, 2016 in hacks by DP | 4 Comments

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Robert Gawron’s home insect electrocution project:

Currently I’m working on a device to electrocute home insects like cockroaches, progress is small because they are smarter than I thought, but that’s a different story. For that project I had to find a source of sufficient high voltage and output power. Presented in previous post 5V/400V converter had insufficient voltage and power, another option, flyback transformer was too dangerous to be used here.
Finally, I have made a new high voltage supply based on an inverter transformer and voltage doubler. It seems to be ok for this job, but it can be used in various other applications so I’m presenting it in a separate entry.

Warning! the device produces high voltage that can be lethal, if you want to build it, please take cautions.

Project info at Robert Gawron’s blog.

Check out the video after the break. (more…)

#FreePCB via Twitter to 2 random RTs

Posted on Tuesday, July 19th, 2016 in Free PCBs by DP | No Comments

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Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.

AD9834 and the IoT beacon

Posted on Tuesday, July 19th, 2016 in RF by DP | No Comments

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m0xpd writes:

I’ve been playing with a new RF generator for the IoT beacon…
Actually, I do myself a disservice, because I’ve done rather more than just play with the RF generator.
First, I’ve replaced the little USB to serial dongle which I used to program the original system and built a complete interface, using the same FTDI chip which was on the original dongle. The thinking behind this is to avoid the requirements for a clumsy interface to some of the more unusual UART lines (such as RTS and DTR), which are not taken out to the nice big header pins on a standard USB-Serial device.
Then, I’ve changed the RF generator – moving from the AD9850 DDS module as used previously to the AD9834 chip. You can see the hardware here…

More details at m0xpd’s ‘Shack Nasties’ blog.

VXO – based PLL frequency synthesizer for 7 MHz

Posted on Tuesday, July 19th, 2016 in DIY by DP | No Comments

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Vasily Ivanenko made a VXO-based synthesizer:

To make a VXO to mix with a ~7 MHz VCO, you’ll need a crystal that is higher in frequency than the highest frequency you want to synthesize. Some rummaging revealed a bag of 21.4773 MHz crystals that I could divide by 3 to garner 7.159 MHz.
To afford a reasonable delta F, three were placed in the super VXO fashion and I applied the smallest amount of series inductance that would ensure a reasonable delta F with solid frequency stability.

Full info at QRP HomeBuilder blog.

App note: Parallel configuration of H-bridges featuring the MC33932 and MC34932 ICs

Posted on Sunday, July 17th, 2016 in app notes by DP | No Comments

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Old application note from ON Semiconductors on getting increased power capability by paralleling H-bridges and overcoming current limit imbalance between the two drivers by properly designing the board layout. Link here (PDF)

Two or more H-bridges can be operated in parallel to increase the current handling capacity of the circuit. In this application note, paralleling of H-bridges has been exemplified using a dual H-bridge model MC33932/MC34932. However, paralleling of H-bridges is not an easy task, as any offset or mismatch between the two MOSFETs can cause one of them to hit the over current/temperature limit before the other, forcing very high-current through one of the H-bridges in parallel configuration, which may initiate device shutdown.

The objective of this application note is to present a method to obtain twice the current from a dual H-bridge by paralleling the dual H-bridges located on the same die. This document also presents the various methods to calculate the junction temperature, to ensure the device operates within the thermal limits specified in the data sheet.

Free PCB Sunday: Pick your PCB

Posted on Sunday, July 17th, 2016 in Free PCBs by DP | 26 Comments

IRToy We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

(more…)

App note: Duty cycle and power optimization

Posted on Sunday, July 17th, 2016 in app notes by DP | 1 Comment

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Power saving specially on battery operated devices need to be kept, in this application note from ON Semiconductors discussed how to keep duty cycle in which a wireless RF device is operated at a minimum time. Link here (PDF)

Consider a battery powered device (target), which should receive data from a second device (initiator) from time to time. To reduce power consumption, the target switches its receiver on for only a short while, checking if there is any RF activity, and returns to sleep if there is no data to receive.

The ratio of the time ton during which the target is powered on, to the time toff during which the target is powered off is called duty cycle. If for example the target is powered off for 1 second, powered on for 1 millisecond, powered off for 1 second and so on, its duty cycle is 1:1000.

Atmel Retrokit SAM D Edition

Posted on Saturday, July 16th, 2016 in AVR by DP | No Comments

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Dan Watson has published a new build, the Retrokit SAM D Edition board:

I created a 2016 re-design of the Retrokit that uses the Atmel SAM D09 microcontroller. This is an excellent 32-bit device that comes in a SOIC package, making it easy to solder. I mimicked the board size and layout of the first Retrokit as closely as possible. The four LEDs are meant to show a comparison in speed between the 32-bit SAM D device, the 16-bit ATxmega, the 8-bit AVR, and the 8-bit PIC microcontroller. There are a lot of devices to select from in each of those families, and if we wanted to be really picky, I could have even chosen a PIC that blew away the little SAM D09. However, I chose representative devices in each category that also demonstrate the development of microcontroller technology over time, from the older PIC 16F series to the modern 32-bit SAM Ds.

Project info at The Sync Channel blog.

Check out the video after the break. (more…)

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