App note: Creating Bluetooth low energy applications using nRF51822

in app notes by DP | 0 comments


An application note from Nordic Semiconductor on creating you own BLE application using their nRF51822 chip. Link here

This application note is intended for anyone who would like to begin programming Bluetooth low energy (BLE) applications on nRF51822. It consists of a general overview of BLE functionality and is followed by a description of a simple example program that implements a custom service, the LED Button service.

Free PCB Sunday: Pick your PCB

in app notes by DP | 48 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:

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App note: Accurate, fast settling analog voltages from digital PWM signals

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Accurate, fast settling analog voltages from digital PWM signals, app note from Linear Technology (PDF!):

Pulse width modulation (PWM) is a common technique for generating analog voltages from a digital device such  as a microcontroller or FPGA. Most microcontrollers have dedicated PWM generation peripherals built in, and  it only takes a few lines of RTL code to generate a PWM signal  from an FPGA. This is a simple, practical technique if  the analog signal’s performance requirements are not  too stringent, as only one output pin is required and the  code overhead is very low when compared to a digital- to-analog converter (DAC) with an SPI or I 2C interface.

Free PCB coupon via Facebook to 2 random commenters

in Free PCBs by DP | 4 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:

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DIY compost sensor

in measurement, sensors by DP | 1 comment


Kinasmith wrote this instructable detailing how to build a compost temperature monitoring system, a web connected wireless sensor network:

Why Measure the Temperature of Compost?
“Composting is the biological decomposition of organic matter under aerobic conditions.” Micro-organisms consume organic material and oxygen and create heat as a waste product. By measuring this heat you can predict decomposition rate, oxygen content (loosely), and the overall health and efficiency of your composting operation. It helps to predict when the pile needs to be turned to introduce more oxygen, when the pile is finished with its hot cook cycle, and if you have effectively killed any pathogens or weed seeds that might be present in the feed stocks. Monitoring is an important aspect to streamlining and creating a stable process and workflow to get a predictable and consistent result through each cook, improving the overall efficiency in the operation.

This project uses short range Radio and Cellular communication to get sensor data from individual probes in the compost to an online database. The hardware will be built on the Arduino platform using the Moteino wireless boards. We will be using thermistors for our temperature sensing, an Adafruit FONA cellular module for our cellular communication and the Sparkfun Data Service for our online database.

DIY double sided 60W LED UV radiation unit with vacuum pump

in DIY, LEDs by DP | 7 comments


Kurt Skauen has been working on a DIY 1188 LED dual sided UV radiation unit:

The UV exposure unit is controlled by an ATmega328P microcontroller and have the following features:

  • Single and double sided exposure. Each side radiated by a 594LEDs / 30W UV LED panel (The unit has a total of 1188 LEDs providing 60W of LED light)
  • The light panels can be calibrated to give even exposure on both sides
  • Built-in vacuum pump for laminating artwork and copper-clad

*The user can define 2-18 speed steps for the vacuum pump

*The vacuum pump can be set to automatically turn off a specified time after the radiation finish

  • Advanced programmable timer / power control for the light panels with 8 persistent presets

Project details at Kavionic blog.


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UC3844 base motor speed controller

in project logs by DP | 0 comments


Dilshan Jayakody writes:

UC3844 is popular current mode controller which is commonly found on DC-to-DC converter circuits and switch mode power supplies. This motor speed controller is also based on UC3844 and it is specifically design to drive 20V – 24V DC motors.
In this given configuration UC3844 produces (approx.) 50kHz to 240kHz PWM output and this range can be adjust by changing the value of C2 timing capacitor. As per the datasheet UC3844 is capable to produce PWM output frequency up to 1MHz.
This circuit is quiet sensitive to the noises, and to get the accurate output construct this circuit on PCB. As per our observations long wires on oscillator circuit may change the stability of the output signal.

Project info at jayakody2000lk’s blog.

DirtyPCBs based project: Isolated USB Serial Interface

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Steve Rodgers just completed another project using a DirtyPCB order, an isolated USB serial interface, that is available at Github:

Here is another project I just completed using a Dirty PCB order. It’s an isolated serial port using the CH340G chip and 4 Silicon Labs Si8410 digital isolators. Isolating the serial port ground from your PC can allow you to work on projects which are floating way above ground potential, or work on projects where ground loops are an issue. For more information please visit my Github site noted above.

Via the contact form.

#FreePCB via Twitter to 2 random RTs

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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.

SIM900 USB Communication using MCP2200

in project logs, USB by DP | 0 comments


Here’s a simple USB interface to communicate with a SIM900 modem by Jesus Echavarria.   He wrote a post on his blog detailing its assembly:

Hi all! Here’s the new project where I’m working a couple of days. Since I develop the SIM900 module and test it, I don’t work with it. Also, I’ve got at home some samples of the MCP2200 USB bridge that I want to test it. So make an USB interface for this board was the perfect idea! This allows to use the SIM900 board with a PC, Raspberry or similar, with the plus of no need external power supply or control signals. Just plug the USB cable on the board and start communicating with the world!

Project details at Jesus Echavarria’s blog.

Via the contact form.

Bus Pirate v3.8 free PCB build

in builds by DP | 0 comments


@tecnotopia tweeted picture of his free Bus Pirate v3.8 PCB build.  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.

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Thoughts and rumors about Hacker Camp Shenzhen & Maker Faire


This past week we rocked Hacker Camp 5 and Shenzhen Maker Faire. It was a huge party, as always, thank you to everyone who came!

Instead of covering the camp and fair directly, we saved the images and chat transcript from the shenzhen_hacker_bei group on WeChat. Nearly 100 hackers, makers, and organizers shared a week long discussion. Hopefully this is a very different  perspective than you’ll get from anywhere else. We’ll clean it up and post it in the forum and blog over the coming week.

China is embracing hacking, making, to an insane extent. Local, provincial, and national governments are all funding hackerspaces and promoting innovation. The Shenzhen Maker Faire is probably the most impressive Maker Faire I’ve ever been to in terms of infrastructure and presentation.

Open source seems to be on fire in China. At the first Shenzhen Maker Fair I explained open source to skeptical locals. This year almost every major product on display was open hardware (or claimed to be…).

Here are some whispers, gossip, rumors, and outright lies overheard at Hacker Camp and Maker Faire. None of this should be taken as true and is totally unverified:

  • Seeed Studio has an new office in a technology park funded by China’s Innofund and is going IPO, possibly a local hacker space too
  • Radio Shack is opening a new chain that finally brings mobile phones to the totally under served Asian market. They will have a section with Hackcelerator projects. #shax
  • Make Block has a paper valuation around 50M
  • Business accelerators are out, decelerators are the new hotness. Keep an eye on this space
  • Whatever remains of Arduino after nasty infighting supposedly doesn’t own the Arduino trademark in China (and some other places). They’ve released Genuino for the Chinese market with a new name, and 39RMB ($6) price tag to complete with 10RMB clones on Taobao. Seeed is manufacturing it. Hey guys, looking for US distributors? #peak-duino
  • While 3D printers are still an enormous part of the fair, it seems to be giving away to wireless dev boards. #50dollar3dprinter
  • Hacker Camp has been an amazing run: 5 camps in 18 months, more than 100 participants. We’ve never met a group of more interesting and talented people. We’re not sure what happens next, but no more camps are scheduled. There will probably be a smaller and more informal successor, we’re still scheming
  • Hack a Day throws a kick sass party with local brews from Joe @ Bionic Brew and China pizza champions NYPD. Thanks guys! #poolsidebusinessmeeting
  • Bunnie is now doing angel funding, slamming down 2 big reds for a new industrial waste stream recovery project. Mike @ Hack a Day’s LED hat was spotted scrolling the name of the same company at the Maker Faire after party. #theexpresswaytogreatness


Free PCB Sunday: Pick your PCB

in Free PCBs by DP | 40 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 | 40 Comments

App note: Low cost I2C level translator

in app notes by DP | 1 comment


2 Diodes, 3 resistors and a transistor here’s Silicon Labs’ low cost solution on voltage level translation. Link here

This applications note discusses a low-cost circuit for I2C level translation. This circuit was developed for the Si701x, Si702x, and Si703x humidity sensors but will work in many applications. This circuit provides I2C level translation from a higher voltage supply, such as 5 V, to a lower voltage, supply such as 1.8 or 3.3 V. In addition, the optional emitter follower circuit provides a low-voltage power supply rail from the higher 5 V supply. Note that some devices allow for higher voltage tolerance on I2C inputs. For example, the Si7034 has a 3.3 V tolerant I2C interface, so the level translation is only required for 5 V I2C designs.

App note: Isolator vs. optocoupler technology

in app notes by DP | 1 comment


Great read from Silicon Labs on comparison of isolation technologies namely optocouplers and digital isolators. Link is here

Optocouplers have been the unchallenged signal isolation solution for more than four decades, but digital isolators fabricated in complementary metallic oxide semiconductor (CMOS) process technology are gaining favor in the design community because of their superior performance, reliability and integration.