DesignNews – Sherlock Ohms: Corroded Copper Stops Dial Ton

Corroded Copper Stops Dial Tone – Dave Boccuti 

A few decades ago, I owned a home in one of Boston's western suburbs. The house had been built during World War II, when nobody with any business building houses was doing so. But that's another story. This one is about the telephone.

One day, I picked up the phone, and there was no dial tone. I went to the neighbor's house (this was before cellphones) and called the phone company to report the problem. The company said it would look into it, so I returned home. A little while later, the phone rang -- it was the phone company asking about the problem. I hung up, checked for a dial tone, and called back to report it was A-OK.

All was fine for a few days, but then the problem came back. I walked over to the neighbor's house, and this time I called my house. My wife answered, and the phone seemed OK.

Read more: DesignNews – Sherlock Ohms: Corroded Copper Stops Dial Ton

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Magic Mote Wireless Sensor Node

Found on Hack-A-Day, from the Magic Smoke blog page.
 
I like this idea.  These RF modules are about a buck a piece and use an SPI interface.  This should be easily adaptable to a PIC processor and Swordfish Basic.
 
 
This compact PCB interfaces a low power MSP430G2553 microcontroller with a Nordic NRF24L01+ 2.4 GHz radio frequency transceiver module. It's well adapted to serve as a wireless sensor node, but has enough I/O options to be put to use wherever a small microcontroller is required. Available soon from Tindie!

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Via Hack-A-Day: Eagle Boards with Customized Shapes

 

h-a-d custom board shapesThis article was found on Hack-A-Day and is repoisted here because it's a useful technique.

Using an OpenSCAD shape as the board outline in EAGLE

Bryan Duxbury

 

I’ve been working on a Charlieplexed LED analog clock. The finished product will be an artfully routed PCB in a clear acrylic enclosure. Since the PCB will be the centerpiece, I want it to be pretty cool looking, including an interesting outline. The design I’m going for pictured below. It’s the union of four different rotations of the convex hull of a central circle and a smaller outer circle. Simple, right?

Read more: Via Hack-A-Day: Eagle Boards with Customized Shapes

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A Look at Switching DC-DC Converters

switcher module - smallTo use my USB charger boards in the car, I need to convert the nominal 12 volt supply to 5 volts at up to 2 amps (a 10 watt output).  The first choice in voltage regulation is often the ubiquitous 78xx (where xx is the desired output voltage).  For low power loads, this is an effective, inexpensive choice, but for higher power applications, these regulators don't work so well.

The input current to a linear regulator will be equal to the output current at the lower voltage plus a negiliable amount to operate the regulator itself.  In this case, the output is 2 amps at 5 volts, equaling a 10 watt output.  The input is therefore 2 amps at 14 volts (when the car is running), which equals 28 watts of input power.  28 watts input for 10 watts output???  Where does the extra 18 watts go?  HEAT.  A nightlight bulb is 4 watts for comparison and that's more than enough to burn your fingers, so 18 watts is a huge waste!  It would take a large heat sink to dissipate this much heat to keep a linear regulator at a safe temperature.

Read more: A Look at Switching DC-DC Converters

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From MAKE - A Pocket Size Power Supply

imageJason Poel Smith likes to shop at thrift stores as do I.  It's nice to be able to test electronics before making the decision to buy, but that can be a challenge for battery-powered gear.  Jason developed a simple LM317 circuit to adjust the output in 1.5 volt steps from a 9 volt battery, so that he can simulate from one to five cells and it connects to the device being tested with alligator clips.  Very ingenious and handy!  Complete instructions can be found in the MAKE Magazine article:  Pocket-Sized Power Supply.

One slight critisium and a common mistake however – the sample circuits shown in LM317 data sheets are based on the LM117 part, which has a lower minimum current draw (5 mA compared to 10 mA).  R1, used to adjust the output voltage, should be 120Ω instead of 240Ω as shown to meet the minimum load requirement to ensure regulation.  The other resistor values will have to be adjusted accordingly.

image copy

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EEVblog #483 – Voltage Inverter Tutorial

EEVBlog 483Dave Jones at the EEVBlog covered voltage doublers in a recent episode.  His latest tutorial covers a variation of the technique, the voltage inverter.  This is excellent technique to have at hand when you need a few milliamps of  negative voltage for a circuit, perhaps for an op-amp circuit or to be able to adjust down to zero volts with an LM317 adjustable voltage regulator.

Dave clearly explains the details in this entertaining tutorial.  It's recommended watching!

EEVblog #483 – Microcontroller Voltage Inverter Tutorial

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Read 10 or more switches using only two I/O pins of a microcontroller

- February 28, 2013

This is a repost from EDN Magazine's Design Ideas

There are several ways to read multiple switch inputs using a reduced number of microcontroller-unit (MCU) pins. For example, you can use an analog MCU pin to read multiple switches by assigning a unique voltage to each switch through a resistor network, or you can use a one-wire device, such as the Maxim DS2408 8-channel addressable switch.

The first method has several disadvantages: The MCU has to have an ADC function, debounce wait times reduce the polling rate, and an error results if the switch is opened during the ADC sampling time. The second method also has the drawback of comparatively low speed; it uses 1-wire communication, which requires continuous polling; and each poll generates an 8-bit data sequence relevant to switch positions.

This Design Idea describes a method for reading multiple pushbuttons or open/closed switches using only two digital I/O pins and a timer interrupt of the MCU (Figure 1). Optionally, a third I/O pin can be assigned to periodically reset the CD4017 (a cascadable decoded 1-of-10 Johnson counter) for reliable operation should an EMI or ESD event occur that could falsely clock the counter, or you can use the circuit shown in Figure 2 and retain the two-pin feature. The diodes isolate the counter outputs in the event that two or more switches are closed at the same time. You can increase the number of switches connected by cascading multiple CD4017 ICs using a carry-out signal (pin 12) and a clock signal (pin 14).

Read more: Read 10 or more switches using only two I/O pins of a microcontroller

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Connect a 4×3 matrix keyboard to a microcontroller using two I/O pins

- May 8, 2013

This is a repost from EDN Magazine's Design Ideas

Matrix keyboards are common as an input device in microcontroller-based projects. A conventional way of connecting a matrix keyboard to a microcontroller is to use multiple I/O pins of the MCU. The MCU then uses a scanning algorithm to identify which keys are pressed. A drawback of this method is that it requires a large number of the MCU’s I/O pins to connect the keyboard. For example, to connect a 4×3 keyboard requires seven digital I/O pins. This becomes a problem when the project is based on a low-pin-count MCU or when the MCU being used does not have enough free I/O pins.

Two solutions for this issue are available: Use readily available I/O expanders, or assign a unique voltage to each key using a resistor network and then use an analog pin to read the voltage and determine which key is pressed. Each solution has its own disadvantages.

Since most of the time I/O expanders require a special communication protocol (I2C or SPI, for example) to read and write data, the MCU should have built-in communication modules, or the user has to implement the relevant communication-protocol software wisely, which adds significantly to the overhead of the MCU. On the other hand, assigning a unique voltage to each key using a resistor network becomes troublesome as the number of keys becomes high, which will lead to tight voltage margins. Then, as resistor values tend to change with temperature, the use of tight voltage margins can cause incorrect readings. Even switch bouncing can play a major role in producing incorrect voltages with this method. Another major drawback of this method is that it requires the presence in the MCU of an analog input pin.

Read more: Connect a 4×3 matrix keyboard to a microcontroller using two I/O pins

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From EDN: One I/O line drives shift register with strobe

& - March 28, 2013

This is a repost from EDN Magazine's Design Ideas.

This Design Idea shows how a single microcontroller port can drive a lot of output lines through shift register. In this case we use the shift register with strobe control to achieve perfect output line control.

Shift register outputs can drive LEDs, relays, etc. In other words, they can be used as (additional) general purpose outputs.

Today there are shift registers that have DATA and CLOCK inputs only, like 74HC164, and shift registers with same inputs plus STROBE control input, like 74HC4094 or 74HC595. The shift registers without STROBE control have short-term transient states at outputs during shifting. Transients occur because shift register is directly connected to output lines. This kind of shift register can be used for driving LEDs and similar devices where short-term transient is irrelevant. For example, the human eye can't notice LED flickers shorter than 10 msec. The shift registers with STROBE control have two registers.

Read more: From EDN: One I/O line drives shift register with strobe

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Color Maximite Computer

I saw reference to the Color Maximite single board computer in Circuit Cellar Magazine and am impressed enough to share it here.  Like desktop computers of old, it has a Basic interpreter built in, along with monitor and keyboard support and an SD card " floppy drive."  The unique feature is that it supports ubiquitous Arduino shields along with I2C, SPI and a number of port pins.  Not bad for $50..  Check out Circuit Gizmos web page for some interesting products.  The description below is from their website.

CGCOLORMAX2  - Color Maximite

Color Maximite-type computer/controller with serial circuit support and prototype area

 

CGCOLORMAX2 - Color Maximite
 
$49.99
US dollar
 
 
Product #CGCOLORMAX2
In stock
Lead-free
 

CircuitGizmos Color Maximite

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