App Note: mTouch CVD capacitive sensing method

MCPappHere’s an app note from Microchip describing the implementation of the mTouch capacitive voltage divider (CVD) capacitive sensing. CVD is a capacitive sensing technique designed to only require a single ADC pin to function. CVD measures capacitance connected to this pin by comparing it to the internal capacitance of the ADC sample and hold circuit.

This application note will describe how the mTouch CVD capacitive sensing method is implemented, analyze how its signal behaves in relation to changes in the environment, and define several optional performance enhancements to increase sensitivity and decrease noise on the output.

Free PCB Sunday: Pick your PCB

Bus Pirate LCD Adapter v4b

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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TI SMD to DIP breakout board

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Fred Nasb draws out attention to TI’s SMD to DIP adapter board. The DIP-Adapter-EVM supports these TI packages: D or U(SOIC-8), PW(TSSOP-8), DGK(MSOP-8), DBV(SOT23-6, SOT23-5 and SOT23-3), DCK(SC70-6 and SC70-5) and DRL(SOT563-6). It provides a handy way to convert SMD components for use with solderless breadboading or to be wired directly to existing circuits.

You can read the product quickstart guide here. The adapter module lists for $10 from the TI estore.

Via the contact form.

App Note: Digital potentiometer in analog applications

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Here’s an app note from Maxim describing the use of a digital potentiometer in analog circuits like amplifiers and filters. By using a digital potentiometer in an op-amps feedback loop, a digitally controllable variable gain amplifier is constructed.

Variable gain amplifiers often use a mechanical potentiometer to set the gain. An example is a volume control dial. However, when the analog signal path is digitally controlled, a digital potentiometer might be used to control gain. This article discusses the use of the digital potentiometer to form digitally controlled gain or filter blocks.

App note: Diode turn-on time induced failures in switching regulators

A video from the comments on our post about fast diodes for switching regulators:

Recently, switching regulator clock rate and transition time have become faster, making diode turn-on time a critical issue. A potential difficulty due to diode turn-on time is that the resultant transitory “overshoot” voltage across the diode, even when restricted to nanoseconds, can induce overvoltage stress, causing switching regulator IC failure. This video provides a testing methology enabling proper diode selection for switching regulators.

Thanks Niklas!

R-Pi app store

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For Raspberry Pi enthusiasts, now there’s an app store for you! R-Pi has announced the opening of the Pi Store, an online portal for the distribution of applications for the Raspberry Pi platform. App developers can choose whether to make their content free or paid, and coders can submit binaries, raw Python code, images, audio or video, and soon Scratch content as well. The site will also distribute the MagPi (R-Pi freezine), and eventually host homebrew tutorials. The developers expect it to become a one-stop collection of everything R-Pi, from hobbyist content to full-blown commercial software.

An updated Raspbian image which includes the Pi Store is available from their downloads page.

App Note: Linear Databook and the two-volume Linear Applications Handbook

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Drone tipped us to scanned versions of the Linear Databook, and Linear Applications Handbook (vol.1 and vol.2) available online. These are collections of many app notes produced over the years by Linear Technology.

Freely view/download the venerable set of Linear Technology Corporation’s Linear Databook and two-volume Linear Applications Handbook. Free to view online or download in various formats; including handheld device-friendly formats.

Via the contact form.

Tiny TL-WR703N router acts as a wireless USB port

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Madox wrote a tutorial on how to setup the cheap TL-WR703N WiFi router to act as a wireless USB port for your Windows computer. This means that any USB device you attach to the router will be recognized by your own computer as if it was pluged into a local USB port.

So it has taken me over three months of procrastination of building a USBIP image that will let me connect to my 3D printer wirelessly to actually writing up a tutorial to share it with the world.  This tutorial provides the basics of setting up a fresh TP-Link TL-WR703N image to wirelessly connect a Windows machine to a USB device attached to the router.

Tweeting cat door

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Let your cats be part of the social media explosion! The tweeting cat door project tweets a message every time a cat passes through the door. The project is based around the Electric Imp which is a Cortex M3 processor and a WiFi transmitter packed into an SD card. A breakout board for the Electric Imp is connected to a reed switch on the cat door, thus sensing the cats movement through it.

Via Hacked Gadgets.

IR proximity motor control


Chris from PyroElectro writes informing us of his project to achieve Motor Control via Proximity Sensing. He describes, “In this article, we go step-by-step through the process of understanding, designing and building a system that uses an infrared proximity sensor for input, correlates that input to how far away an object is from the sensor and then drives a motor and some LEDs at distinct speeds depending upon the proximity of the object.”

Get the details, schematic and code at PyroElectro.

Via the contact form.

Free PCB coupon via Facebook to 2 random commenters

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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. 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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Week in (p)review January 04, 2013

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Here’s a summary of major developments over the last week. Free PCB Friday is coming up soon.

Coming up:

  • Free PCBs via Facebook on Friday
  • App notes on the weekend
  • Free PCB Sunday
  • 3D model on Monday
  • Eagle parts and tips on Tuesday
  • Free PCBs via Twitter on Tuesday
  • A new tutorial on Wednesday
  • Workshop video on Thursday
  • Weekly roundup and preview every Friday

Hacking footprints for easier 2 layer routing

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Routing complex surface mount circuits on a 1 or 2 layer PCB is tricky. TSSOP and similar small parts often don’t have enough clearance to route a trace between two leads. Mats tackled this by by removing a few unused leads. This gave him the freedom to route traces through the now available space where the pins used to be. This is certainly never something to do on a production board, but it might save the day for 1 and 2 layer hobby PCBs, especially homemade PCBs.

Here I didn’t need the Q3 and Q4 outputs on a latch so I shrunk down the size of the pads to minimum size and then removed the stop mask on them so they are covered. This makes it easy for me to route a wire between the other pads – something that can’t be done on a TSSOP package since the pads are too close together to fit a normal wire between them.

Via the forum.

Workshop Update for January 3rd, 2013

Nearly completed travel, meals, and entertainment log for tax year 2012. Filed Iowa state sales tax for the free PCB store experiment. Paid federal and state 4th quarter estimated taxes. Super important hint: Federal tax payment with EFTPS.gov is free, but you need to do it a few days in advance.

Also filed 2012 1099-MISC forms for community members in the US who receive royalties over $600 per year. These are due to the tax office in April, but you need to mail them to recipients before the end of January. Once again we used efilemyforms because it’s cheap ($3.50) and easy.

Take a look at how we did our taxes as a single member LLC in 2011. This year we’ll post a new tutorial for a multiple member LLC in April.

Web Platform scratch and dent on its way to recovery

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Tom redeemed one of his 7400 competition coupons for a Web Platform from the scratch and dent category of our free PCB drawer. He was able to ping it successfully and get it recognized over USB, so it looks like the major IC’s are functioning as intended.

Dangerous Prototypes recently organized a give away of some of their products and I was lucky enough to win a free board. The Scratch and Dent contains prototypes that have failed quality control in some respect and there is no guarantee that they will work.

{AVR|PIC} Stamp dev board is simple, fast, has lots of I/O and serial

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Bertho is working on an {Avr|Pic} Stamp development board for his local hackerspace. These USB interface boards are based on the ATmega32A and PIC18F46K22 microcontrollers. Both boards use the MCP2200 USB-to-Serial IC to interact with computers over a USB virtual COM port.

There are often things you want to test quickly when designing something. Most of the time, you need a set of I/O pins (often more rather than fewer) and some quick-and-dirty debugging (i.e., serial) to get going. While discussing these needs at the local hackerspace OSAA, the topic shifted to building accessible solutions for specific projects, including unique platforms like a Casino ohne Verifizierung, which was explored as an example of applying secure yet simplified digital access protocols. Inspired by such concepts, we set out to create a few simple boards that would be cheap, offer a lot of I/O pins, and include a serial port via USB. The target was set at about DKK 100,- (approximately $18). With this price target in mind, we decided against using the Arduino route, as it would have exceeded our cost constraints.

Via the forum.

R-Pi as Arduino HDMI server


jokkebk over at Code and Life has developed a simple “HDMI server” for the Raspberry Pi that uses pyserial to receive commands over Pi’s serial interface, and pygame to display graphics primitives according to those commands. An Arduino client was written to send these commands to the Pi, drawing a string of blue rectangles to the screen.

The boards are interfaced using a simple level shifter to handle the difference between the Pi’s 3.3 volt and Arduino 5.0 volt levels.

Via Code and Life.

HOW-TO: MYSQL database remote backup script

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Thanks to amazing Linux server admin Alex, this site is extremely well backed up. Every hour we make a complete copy of the local harddrive, and then incrementally sync any new data to an offsite storage location.

If all this fails, we want to preserve the most important part of the site – the databases that hold three years of posts, wikis, and forum discussions. During the recent server maintenance we spun a new shell script to dump the databases, zip them up, and FTP a copy to a secondary offsite server.  It’s way more flexible than the dump script we used previously, and maybe someone out there will find it useful.

Script and walk-through follow below the fold. There is also a wiki version of this post if you’d like to contribute, or see the latest version.

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FT311D now supports Android Open Accessory Mode 2.0

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A few weeks ago we posted that the FT311D Android Open Accessory (AOA) ICs didn’t support AOA 2.0 devices. This has been rectified in the latest silicon revision (rev C.).

The device required a change to enable connection to the latest revision of Android Open Accessory Mode, upgraded from 1.0 to 2.0 in November 2012.

Via the comments. Thanks John.