IR Remote Control Testing (EE Tip #119)

On the Internet you can find them in all shapes and sizes: circuits to test remote controls. Here I describe a simple and cheap method that is not that well-known.

This method is based on the principle that an LED does not only generate light when you apply a voltage to it, but also works in the opposite direction to generate a voltage when light falls on it. Within constraints it can therefore be used as an alternative for a proper phototransistor or photodiode. The major advantage is that you will usually have an LED around somewhere, which may not be true for a photodiode.

IR remote tester

IR remote tester

This is also true for infrared (IR) diodes and this makes them eminently suitable for testing a remote control. You only need to connect a voltmeter to the IR diode and the remote control tester is finished. Set the multimeter so it measures DC voltage and turn it on. Hold the remote control close to the IR diode and push any button. If the remote control is working then the voltage shown on the display will quickly rise. When you release the button the voltage will drop again.

However, don’t expect a very high voltage from the IR diode! The voltage generated by the diode will only be about 300 mV, but this is sufficient to show whether the remote control is working or not. There are quite a few other objects that emit IR radiation. So, first note the voltage indicated by the voltmeter before pushing any of the buttons on the remote control and use this as a reference value. Also, don’t do this test in a well lit room or a room with the sun shining in, because there is the chance that there is too much IR radiation present.

To quickly reduce the diode voltage to zero before doing the next measurement you can short-circuit the pins of the diode briefly. This will not damage the diode.—Tom van Steenkiste, Elektor, 11/2010

Want tips about testing power supplies? We’ve got you covered! EE Tip #112 will help you determine the stability of your lab or bench-top supply!

Infrared Communications for Atmel Microcontrollers

Are you planning an IR communications project? Do you need to choose a microcontroller? Check out the information Cornell University Senior Lecturer Bruce Land sent us about inexpensive IR communication with Atmel ATmega microcontrollers. It’s another example of the sort of indispensable information covered in Cornell’s excellent ECE4760 course.

Land informed us:

I designed a basic packet communication scheme using cheap remote control IR receivers and LED transmitters. The scheme supports 4800 baud transmission,
with transmitter ID and checksum. Throughput is about twenty 20-character packets/sec. The range is at least 3 meters with 99.9% packet receive and moderate (<30 mA) IR LED drive current.

On the ECE4760 project page, Land writes:

I improved Remin’s protocol by setting up the link software so that timing constraints on the IR receiver AGC were guaranteed to be met. It turns out that there are several types of IR reciever, some of which are better at short data bursts, while others are better for sustained data. I chose a Vishay TSOP34156 for its good sustained data characteristics, minimal burst timing requirements, and reasonable data rate. The system I build works solidly at 4800 baud over IR with 5 characters of overhead/packet (start token, transmitter number, 2 char checksum , end token). It works with increasing packet loss up to 9000 baud.

Here is the receiver circuit.

The receiver circuit (Source: B. Land, Cornell University ECE4760 Infrared Communications
for Atmel Mega644/1284 Microcontrollers)

Land explains:

The RC circuit acts a low-pass filter on the power to surpress spike noise and improve receiver performance. The RC circuit should be close to the receiver. The range with a 100 ohm resistor is at least 3 meters with the transmitter roughly pointing at the receiver, and a packet loss of less then 0.1 percent. To manage burst length limitations there is a short pause between characters, and only 7-bit characters are sent, with two stop bits. The 7-bit limit means that you can send all of the printing characters on the US keyboard, but no extended ASCII. All data is therefore sent as printable strings, NOT as raw hexidecimal.

Land’s writeup also includes a list of programs and packet format information.

Infrared Communications for Atmel Microcontrollers

Are you planning an IR communications project? Do you need to choose a microcontroller? Check out the information Cornell University Senior Lecturer Bruce Land sent us about inexpensive IR communication with Atmel ATmega microcontrollers. It’s another example of the sort of indispensable information covered in Cornell’s excellent ECE4760 course.

Land informed us:

I designed a basic packet communication scheme using cheap remote control IR receivers and LED transmitters. The scheme supports 4800 baud transmission,
with transmitter ID and checksum. Throughput is about twenty 20-character packets/sec. The range is at least 3 meters with 99.9% packet receive and moderate (<30 mA) IR LED drive current.

On the ECE4760 project page, Land writes:

I improved Remin’s protocol by setting up the link software so that timing constraints on the IR receiver AGC were guaranteed to be met. It turns out that there are several types of IR reciever, some of which are better at short data bursts, while others are better for sustained data. I chose a Vishay TSOP34156 for its good sustained data characteristics, minimal burst timing requirements, and reasonable data rate. The system I build works solidly at 4800 baud over IR with 5 characters of overhead/packet (start token, transmitter number, 2 char checksum , end token). It works with increasing packet loss up to 9000 baud.

Here is the receiver circuit.

The receiver circuit (Source: B. Land, Cornell University ECE4760 Infrared Communications
for Atmel Mega644/1284 Microcontrollers)

Land explains:

The RC circuit acts a low-pass filter on the power to surpress spike noise and improve receiver performance. The RC circuit should be close to the receiver. The range with a 100 ohm resistor is at least 3 meters with the transmitter roughly pointing at the receiver, and a packet loss of less then 0.1 percent. To manage burst length limitations there is a short pause between characters, and only 7-bit characters are sent, with two stop bits. The 7-bit limit means that you can send all of the printing characters on the US keyboard, but no extended ASCII. All data is therefore sent as printable strings, NOT as raw hexidecimal.

Land’s writeup also includes a list of programs and packet format information.

In Memoriam: Richard Alan Wotiz

Richard Alan Wotiz—a multitalented electronics engineer, inventor, and author—provided the international embedded design community with creative projects and useful electronics engineering lessons since the early 1980s when he graduated from Princeton University. Sadly, Richard passed away unexpectedly on May 30, 2012 while hiking with a group of friends (a group called “Take a Hike”) in Santa Cruz County, California.

Richard Alan Wotiz

Richard started writing his “Embedded Unveiled” column for Circuit Cellar magazine in 2011. You can read each of his columns by clicking the links below:

Prior to becoming a columnist, Richard placed highly in several international embedded design challenges. Amazingly, he won First Prize in both the Texas Instruments 2010 DesignStellaris Challenge and the 2010 WIZnet iMCU Challenge. That’s right—he won First Place in both of Circuit Cellar’s 2010 design challenges!

Richard published intriguing feature article about some of his prize-winning projects. Interestingly, he liked combining his passion for engineering with his love of the outdoors. When he did so, the results were memorable designs intended to be used outdoors: a backpack water level monitor, an earth field magnetometer, and an ABS brake system for a mountain bike.

Richard’s ABS system is built around a Texas Instruments EKK-LM3S9B96 evaluation board, which contains the Stellaris LM3S9B96 microcontroller and support circuitry. The mechanism mounts to the front fork in place of the reflector, and the control unit sits on a bracket that’s also attached to the handlebars. A veritable maze of wires runs to the various sensors on the brake levers and wheels.

His other projects were well-built systems—such as his single-phase, variable-speed drive for AC induction motors—intended to solve real-world problems or handy DIY designs—such as his “Net Butler” network control system—that he could use in his daily life.

Richard’s single-phase, variable-speed drive for AC induction motors is an excellent device for powerful, yet quiet, pump operation. Designed for use with a capacitor-start/capacitor-run motor, it includes active power factor correction (PFC) and inrush current limiting. This is the drive unit. A Microchip Technology dsPIC30F2020 and all of the control circuitry is at the upper right, with all of the power components below. The line filter and low-voltage supplies are in a separate box to the left. It’s designed to sit vertically with the three large filter capacitors at the bottom, so they stay as cool as possible.

Richard named his finished network control system the “Net Butler.” This innovative multifunctional design can control, monitor, and automatically maintain a home network. Built around a WIZnet iMCU7100EVB, the design has several functions, such as reporting on connected network devices and downloading Internet-based content.

I last saw Richard in March 2012 at the Design West Conference in San Jose, CA. As usual, he stopped by our booth to chat about his work and Circuit Cellar magazine in general. He had a great passion for both, and it showed whenever I spoke with him. He was a true believer of this magazine and its mission. During our chat, he asked if he could write about the seven-processor Intel Industrial Control Robotic Orchestra system on display at the conference. I agreed, of course! His enthusiasm for doing such an article was apparent. Soon thereafter he was at the Intel booth taking photos and notes for his column.

I’m happy to announce that the column—which he titled “EtherCAT Orchestra”—will appear in Circuit Cellar 264 (July 2012).

Richard’s work was a wonderful contribution to this magazine, and we’re grateful to have published his articles. We’re sure Richard’s inventive design ideas and technical insight will endure to help countless more professionals, academics, and students to excel at electronics engineering for years to come.