#FreePCB via Twitter to 2 random RTs

in Free PCBs by DP | 0 comments


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.

Tutorial: Using GNU profiling (gprof) with ARM Cortex-M

in tutorials by DP | 0 comments


Erich Styger of MCUonEclipse writes, “I have published a Sneak Preview how GNU gprof profiling looks for an embedded target ARM Cortex-M in an earlier post.
This tutorial explains how to profile an embedded application (no RTOS needed) on ARM Cortex-M devices with GNU gprof. Additionally I explain the inner workings to generate the data necessary for gprof.”

An Android reflow controller that anyone can build

in Android, DIY by DP | 0 comments


Andy Brown published a new build, an Android reflow controller:

 The only surface mount device on this PCB is the MAX31855 and it has a low number of generously spaced pins. I eschewed my hot air gun, previous reflow oven and hot plate in favour of a plain old iron and the tack-soldering method because I wanted to show how easy it is to assemble this PCB and you can see me soldering the MAX31855 in the video that accompanies this article. No laughing at the back please; it’s hard to solder from behind a video camera!

Project info at Andy’s blog.

Check out the video after the break. Continue reading →

Posted in Android, DIY | Tagged , | Leave a comment

App note: Overview of USB battery charging revision 1.2 and the important role of charger detectors

in app notes by DP | 1 comment


Ever wonder why USB connector’s power are longer than the D+ D- pads?  Here’s an app note from Maxim Integrated about these detection proccess and their importance. Link here (PDF)

This application note explains details of the USB Battery Charging Specification 1.2, and the role of charger detection. With the use of charger detection ICs, the USB connector on a portable device becomes a versatile component. The built-in BC1.2 compliance keeps the implementation clean and simple to use.
When designing a compact and portable product, the wealth of features accompanying charger detection ICs make them an extremely attractive integrated circuit.

Free PCB Sunday: Pick your PCB

in Free PCBs by DP | 41 comments


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:

Continue reading →

Posted in Free PCBs | Tagged | 41 Comments

App note: Get a constant +5V output by switching between a +5V input and a single-cell LI+ rechargeable cell

in app notes by DP | 0 comments


App note from Maxim Integrated on providing smooth power from two sources. Link here (PDF)

Design provides a simple method for maintaining an uninterrupted +5V even while switching between the external +5V supply and a rechargeable single-cell Li+ battery.

App note: Low drop fixed and adjustable positive voltage regulators

in app notes by DP | 1 comment


Low drop fixed and adjustable positive voltage regulators application note (PDF!) from ST:

The LD1117A is a low drop voltage regulator able to provide up to 1 A of output current, available also in adjustable versions (VREF = 1.25 V). In fixed versions, the following output voltages are offered: 1.2 V, 1.8V, and 3.3 V. The device is supplied in: SOT-223, DPAK and TO-220. Surface mounted packages optimize the thermal characteristics while offering a relevant space saving advantage. High efficiency is assured by an NPN pass transistor. Only a very common 10 μF minimum capacitor is needed for stability. Chip trimming allows the regulator to reach a very tight output voltage tolerance, within ± 2% at 25 °C.

Posted in app notes | Tagged | 1 Comment

Windows 10 IoT core controlling a Raspberry Pi 2 robot

in R-Pi, robotics by DP | 0 comments


Windows 10 IoT Core running a Raspberry Pi 2 robot by Scott Hanselman:

Starting with a Raspberry Pi 2, walk through the setup instructions here. You do need to have a Windows 10 today to installing Windows 10 IoT Core but at least it’s gotten a lot easier with the latest build for IOT. There’s an app that does all the work and you don’t need to go to the command line. Also get Visual Studio 2015 Community and the Windows IoT Core Project Templates. Basically just follow these step-by-step instructions.

Project info at Scott’s blog.

Check out the video after the break. Continue reading →

Free PCB coupon via Facebook to 2 random commenters

in Free PCBs by DP | 2 comments


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:

Continue reading →

Posted in Free PCBs | Tagged | 2 Comments

Simple pendulum tiltmeter

in project logs by DP | 0 comments


Jbeale shared his tiltmeter project in the forum:

Apparently the most popular sensor for this purpose is an “electrolytic tilt sensor”, basically a bubble level with internal electrodes. These are not exactly consumer items. I tried building a simple pendulum tiltmeter using a split-photodiode, Optek OPR2100 (about $10 from Mouser) and LF411 opamp. The pendulum is a 0.064 x 3/4″ x 12″ strip of brass (K&S Metals #8247). Light from a 3W LED shines through a slit at the bottom of the pendulum into the detector. I have the photodiodes in zero-bias mode, wired anode-to-cathode so in balance, the current from one photodiode circulates through the other photodiode. This way the opamp only sources or sinks current (into the photodiodes, through feedback resistor Rf = 1 Mohm) when there is an imbalance in the photodiode current (= light level). I used a LF411 at +/- 15 V because I had it handy; I guess a more modern design would use a 5V single supply opamp and generate a 2.5V midpoint reference somehow. The pendulum will swing a long time unless damped, so I used a magnet assembly from an old hard disk drive for damping (eddy currents in the brass pendulum provide the force), this worked nicely.

Via the project log forum.

Are my documents safe in the root cellar at ~80% humidity?

in hacks by DP | 4 comments


luckyresistor has been working on his Data Logger project:

There is a large cellar where I could store unused items and documents, but the catch is the humidity there. It is a root cellar near a small brook and the humidity varies between 75% up to 90%.
Archived material should never be exposed to humidity greater than 65%, therefore I have to isolate all documents in boxes from the air of the cellar. But are this boxes safe? Do they keep the humidity away from the documents – even for years?
To have a look into the box environment, I need a data logger. It would be simple to buy one, but much more fun to build one. So a new project is born: I call it the “Data Logger” project.

More details at luckyresistor’s blog.

Posted in hacks | Tagged , | 4 Comments

MQTT/JQUERY/WebSockets controller

in site, software, wireless by DP | 0 comments


Peter Scargill writes:

I wrote a while ago about using web sockets as against something like NETIO for controlling the home – most folk liked the article but I think part of it was a little complicated – and at the time I’d not really thought it out to make it as simple as possible.
So, this morning I started again and now I have a decent and easy way to make control interfaces from the mobile phone – to ESP boards. I won’t go into MQTT in detail here – I’ll assume you have an MQTT interface of some description on your WIFI boards – if you need more info on that, look elsewhere on the blog.

Yet another Bus Pirate free PCB build

in builds by DP | 0 comments


idpromnut built a free Bus Pirate v3.8 PCBs. The Bus Pirate is an open source hacker multi-tool that talks to electronic stuff.

If you build a free PCB we’ll send you another one! Blog about it, post a picture on Flicker, whatever – we’ll send you a coupon code for the free PCB drawer.

Get your own handy Bus Pirate for $30, including world-wide shipping. Also available from our friendly distributors.

Via the forum.

Check out the video after the break. Continue reading →

Using input impedance to measure current

in measurement by DP | 2 comments


Using input impedance to measure current, see the detailed blog post here from Sigzig:

Input impedance on measurement equipment is usually kept as high as it can in an effort to prevent loading down the signals the equipment is measuring. For example most general purpose digital multimeters aim for an input impedance of at least 1M ohm. The Zig-4 has a lower input impedance of 330k ohms but this is still high enough for many/most situations. That being said it is still important to understand input impedance and its affect on your measurements.
In this post I thought it would be fun to actually take advantage of the 330k input impedance of the Zig-4 as a sort of low current sensing.
The goal: To see if we can use the Zig-4 to detect a change in current in the very low nA range.

Bus Pirate v3.8 free PCB build

in BP v3, builds by DP | 0 comments


Mark Stewart built two free Bus Pirate v3.8 PCBs.  The Bus Pirate is an open source hacker multi-tool that talks to electronic stuff.

If you build a free PCB we’ll send you another one! Blog about it, post a picture on Flicker, whatever – we’ll send you a coupon code for the free PCB drawer.

Get your own handy Bus Pirate for $30, including world-wide shipping. Also available from our friendly distributors.

Via Twitter.

A JTAG/XSVF library for Arduino

in Arduino, JTAG by DP | 1 comment


Marcelo published a post on his blog about JTAG and the library he wrote.

I have recently felt the need to incorporate a JTAG port in a project to program a hardware that contained a CPLD. The idea was to both program it and perform some integrity tests on the board. I imagined something using pogo pins, to make it easier and quicker to test everything. I would also write the necessary test routines and generate some kind of report.
With this objective in mind, I have decided to design an Arduino shield to do the job. The testing routines were not really a big deal. And I was sure I would find some JTAG library for Arduino ready to be used. That was not the case.
There were some projects using Arduino to control a JTAG TAP (Test Access Port), but they were all incomplete. And I had no idea what was really JTAG. So I had to study a little bit to make things work for me.
In the end, the challenge proved enlightening. There were some caveats, both from hardware and from software. I’ll try to address them in this article.

The library is hosted on Github.

More details at Marcelo’s EE & CS blog.

Posted in Arduino, JTAG | Tagged , , | 1 Comment

Testing the Shinyei PPD42NS

in Arduino, sensors by DP | 5 comments


From the comments on our Arduino dust sensor post,  KH writes:

The sensor can obviously measure dust concentrations, it also has to be placed and set up properly, and it gives useful readings. For hobby users like most of us, obviously calibration to specific or absolute standards will be almost impossible.

More details at Darell Tan’s blog.

Via the comments. Thanks KH!