Decoupling capacitors explained

Bertho, winner of the 7400 contest with his Capacitive Sensing, the Hard Way entry, made an excellent tutorial on the use of decoupling capacitors:

While enjoying the 7400 contest, it occurred to me that many of the submitted logic designs lacked some of the most elementary safeties to ensure a working result. One of the most disregarded aspects of the designs was the lack of bypass capacitors. Then, with an article about Murphy’s law linking a Maxim application note, it was decided to write a bit about decoupling and bypass capacitors.

Via Adafruit.

PID library for Arduino

Arhi tipped us to a PID library for Arduino. If you require precision control of electro-mechanical devices like heaters, servos, water pumps, etc. PID is one  way to implement that control.

It is an algorithm that controls a device by constantly adjusting its control or power signals to keep the device at preset state. Using sensors to detect differences between the preset state and the actual state the device is in, the controller calculates which signals it should send to the device to eliminate the difference. 

Via the forum.

Light sequencing and decoding DMX with Arduino


Akiba of Freaklabs and the Tokyo Hackerspace has written an excellent tutorial on using the Arduino to decode the DMX protocol, a standard protocol for stage lighting displays. It includes a three-part video presentation (Part I, above) and a link to the source code.

As Akiba notes, these techniques could be used in developing some serious Arduino controlled holiday lighting displays.

Via MAKE.

Tweephone analog Twitter client


UP Digital Bureau and Unteleported tech agency present the Tweephone, an analog Twitter client. In the world of short messaging this is about as retro as you can get. Remove the phone from the switchhook, use the rotary dial to enter your message (with the appropriate number of dial rotations to get the letter you desire, similar to a cellphone keypad). You message appears on the LCD screen, and to send just hang up the phone. The messages appear on the Tweephone’s Twitter account.

You can find the Arduino sketch on the project’s Github page.

Partlist Wednesday: Lithium-polymer battery charger chips

Lithium-polymer batteries are an excellent choice for portable projects. They are relatively cheap, hold a significant charge, and last for a long time. The drawback with these batteries is that they require rather complicated charging protocols. You have to watch out for overcharging, undercharging, overheating, etc…

We are looking for a standard part to use in our projects, so we decided to do a roundup of open source lithium polymer chargers from SparkFun, Seeed Studio, and Adafruit. With the exception of Seeed, all the chargers are based on Microchip’s MCP738xx family of battery management ICs that come in SSOP and DFN packages. They handle all the charging algorithms and usually only require a single external capacitor.

Lithium Polymer USB Charger and Battery from SparkFun is a basic charger designed around the MCP73831 IC. A solder jumper changes the charge current from 100mA to 500mA. LiPoly Fast Charger, also from SparkFun, supports currents up to 1A. This design uses the MCP73843 IC driving an external mosfet that handles higher current. 

Seeed is up next with their Li-Po rider and Li-Po rider pro charger/power supplies. They are based on the CN3065 battery management IC. The charge current is 400mA when a powerful enough source is available. One thing to note is that Li-Po riders are not chargers but compact portable power supplies that deliver 5V at 350mA. Battery voltage is converted to 5V through a switching step up converter. The pro version delivers up to 1A of current. 

Adafruit’s USB/DC Lithium Polymer battery charger uses the MCP73861 IC. A charging current of up to 1.2A can be selected through a resistor. This IC has thermal protection. A standard 10K thermistor can be added to the battery to shut down charging in case of overheating. Their USB LiIon/LiPoly charger uses the MCP73833 IC, and is similar to the previus product. This one doesn’t have the DC IN jack populated, and the maximum current is 1A.

After looking at what everyone is using we are going to add the MCP73833 to our part box. It is cheap, has programmable current, and thermal protection through a thermistor. We also liked Seeed’s use of a dc/dc converter for portable projects.

IOIO andriod development board gets bluetooth support

Ytai demoed an IOIO android development board over Bluetooth. Connect the board to your Android enabled device and control various IO pins on the board:

IOIO is a board providing I/O connectivity for Android. Until recently it would use a USB connection for communicate with Android. Yesterday, I announced Bluetooth support, which is achieved by plugging any standard (and cheap) Bluetooth dongle into the USB jack. Using the new feature is a simple matter of firmware upgrade, achievable either with a programmer or with another IOIO.

Via the forum.

XC9572XL breakout board: Frequency counter

Jason implemented a frequency counter on an XC9572XL CPLD. It uses a 1Mhz clock to count the duration of the input signal pulse, and shows the output on a 6 digit display.

Initially he had to use additional 7400 logic ICs to convert BCD output from the CPLD to the 7-segment displays. With some tweaking of VHDL code he was able to squeeze it into the CPLD as well.

Get your own XC9572XL based CPLD dev board for $15 and start experimenting with programmable logic today.

Via the forum

Open 7400 competition winners

Thank you participating in the Open 7400 Competition. All the entries were amazing, check out the full list here.

Four judges, Dave Jones from EEV Blog, Jayson Tautic CEO of TAUTIC ELECTRONICS LLC, Marc Alexander from Freetronics, and Dino Segovis from Hack A Week, and Ian from Dangerous Prototypes each made a top ten list. The projects with the most votes were awarded prizes.

Winners will receive prize information by email in the next 48 hours. As digital currencies gain traction in everyday transactions and online leisure activities, we want everyone to get a prize they can use and enjoy. You can pick your own prizes through the free PCB store or choose Bitcoin allocations redeemable across various platforms, including roulette sites that accept Bitcoin. First place winners will pick first, followed by second, then third. Remaining prizes will go to anyone who entered the contest, enhancing engagement with these versatile digital reward options.

With unanimous consent of all judges, and also the reader’s choice winner, 7400 Capacitive Touch Array (Capacitive touch sensing the hard way) wins the grand prize of $100 and first pick of the prizes.

Also a top ten of all judges, the 7400-based Capacitance Meter wins first place and next pick from the prizes.

Nine entries took second place with votes from 2 judges. These winners get next pick from the prizes.

22 entries placed third with the vote of at least 1 judge. They get to pick a prize too.

Thanks again for entering, we hope to see you again next year! Thanks to the sponsors, our judges, Dave Jones, Jayson Tautic, Marc Alexander, and Dino Segovis, Sven for the contest artwork, and the creative mind behind the 7400 Contest SQKYbeaver. Continue reading “Open 7400 competition winners”

DesignSpark chipKIT Challenge


Manuel writes to inform us of the DesignSpark ChipKIT Challenge. According to the contest page, “[p]articipants in this competition must use Microchip’s chipKIT Max32 development board to design an energy-efficient and eco-friendly device. Entries must include an extension card developed using DesignSpark’s PCB tools, should compile using Microchip’s MPLAB IDE software and will be judged on their level of energy efficiency and quality of the extension card’s PCB design.” There are $10,000 in cash and prizes listed.

The challenge is making 1000 chipKIT boards available for contest entrants, so register beginning November 28. You can view the official rules at the DesignSpark site. Deadline for submissions is March 27, 2012, but we suspect the supply of free dev boards will disappear quickly.

Via the contact form.

Bootstrapping a PICqueño32

After populating his free PICqueño32 board with the microcontroller, Schazamp wanted to program it to check if his soldering was OK. Unfortunately he didn’t have a PIC programer, so he decided to build his own.

He built a PICKIT2 clone, but that programer also uses a PIC uC. He had to build the simple JDM2 serial port programer to get his PICKIT2 clone working, and then subsequently his PICqueño32.

Via the forum.

PIC 16F1507 SSOP20 breakout board

After buying a few PIC16F1507s from Microchip, Dolabra is building a breakout board for their SSOP 20 pin package.

Earlier this part was not supported by PICKIT2, and he had no way of programing them. As a stroke of luck Microchip added an updated device file for the PICKIT2 and saved him a lot of aggravation. The device file enables the PICKIT2 to program many of the new Microchip devices that were previously unsupported.

Via the forum.

In development: Soldering iron driver

Earlier this year Arhi developed a soldering iron driver (machine translation) that works with both PTC and K-type TC temperature sensors. In this design a microcontroller implements PID temperature control of the soldering iron, and shows the relevant information on a display. His posts in the forum inspired us to build one too.

The soldering iron type is selected by jumpers. The actual temperature is read by amplifying the sensor signal with an op-amp, and feeding it to the analog to digital converter input of the uC.

Our version of his driver adds a few things to Arhi’s design. It has both a UART and USB interface that can control and monitor the soldering iron, and update the firmware. We added a button and an extra LED. The button switches the heater on and off while the driver is still on.

Our board uses a single layer and all through hole components, so it can be etched at home. The minimum trace width was set to 16mil, and the spacing to 14mil, to make it as simple as possible for people to make DIY boards.

The amplifier output, 5v power supply, ON/OFF button, and the triac jumper are broken out to allow for easier prototyping and further development.

While the current version uses the 24VAC input from a soldering station transformer, one future goal is to make our board laptop power supply friendly.

A special thanks to Arhi for releasing his open source soldering iron driver, and his help with our design.

Openschemes homebrew SVF player


Openschemes has a tutorial describing their project for bit bang JTAG programming of Xilinx CPLDs using their homebrew SVF player. They describe:

Today’s lesson consists of the development of a bit-banged JTAG SVF player in order to program a device such as a CPLD. It’s quite likely that the SVF player we develop today could program an FPGA or flash a micro or some other good stuff we haven’t thought of yet – SVF is a very powerful data format. But at the moment, we’re going to stick to the task at hand – flash a bitstream to a CPLD using a homebrew JTAG interface.

Openschemes invites you to download and experiment with their FT232 SVF player.

#FreePCB via Twitter to 2 random RTs

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

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

Continue reading “#FreePCB via Twitter to 2 random RTs”

Bus Blaster hack: Flashing a PC BIOS chip

Zougloub modified the Bus Blaster V2 somewhat and successfully flashed a PC BIOS chip. By using the onboard FTDI FT2232H chip in SPI mode, and slightly modifying the CPLD logic, he successfully established a link to the BIOS chip. He was now able to update his BIOS and use a processor with his motherboard that wasn’t supported out of the box.

Via the forum.

You can get a Bus Blaster v2 for $34.95

UBW32 board

UBW32 is an open source project that allows users to write and read 70+ IO pins through USB. TitanMKD added his blog site on the silkscreen and got 10 PCBs built by Seeed.

He is currently developing a project that uses the NFC shield to communicate with RF ID cards. So far he has been successful identifying the cards and reading all the sectors on them.

Via the forum.