70016 Parallax Inc, 70016 Datasheet - Page 15

• Manufacturer Part Number: 70016
• Description: TEXT INFRARED REMOTE FOR BOE-BOT
• Manufacturer: Parallax Inc

Specifications of 70016

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Boe-Bot®
• For Use With: 29122 - KIT PARTS IR REMOTE FOR BOE-BOT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

The IR receiver the Boe-Bot used for infrared object detection in Robotics with the Boe-
Bot is the same detector found in many TVs and VCRs. This detector sends a low signal
whenever it detects IR flashing on/off at 38.5 kHz and a high signal the rest of the time.
When the IR detector sends low signals, the processor inside a TV or VCR measures how
long each of the low signals lasts. Then, it uses these measurements to figure out which
key was pressed on the remote. Like the processor inside a TV or VCR, the BASIC
Stamp 2 can be programmed to detect, measure, store, and interpret the sequence of low
pulses it receives from the same IR detector.
There are many different communication protocols that a universal remote can use to
transmit PWM messages to entertainment system components. This text will focus on
the SONY protocol. It is easy to understand, and it works well with the same IR detector
that we used for infrared object and distance detection in Robotics with the Boe-Bot.
Figure 1-4 shows a timing diagram example for an example signal the IR detector might
send to the BASIC Stamp when it receives a SONY TV control message from the IR
remote. This message consists of thirteen negative pulses that the BASIC Stamp can
easily measure. The first pulse is the start pulse, which lasts for 2.4 ms. The next twelve
pulses will either last for 1.2 ms (binary-1) or 0.6 ms (binary-0). The first seven data
pulses contain the IR message that indicates which key is pressed. The last five pulses
contain a binary value that specifies whether the message is intended being sent to a TV,
VCR, CD, DVD player, etc. The pulses are transmitted in LSB-first order. This stands
for least significant bit first, meaning the first data pulse is bit-0, the next data pulse is
bit-1, and so on. If you press and hold a key on the remote, the same message will be
sent over and over again with a 20 to 30 ms rest between messages.
Pulse width modulation (PWM): Pulse durations are used in many applications, a few of
which are digital-to-analog conversion, motor control, and communication. Since the IR
detector sends low pulses that can be measured to determine what information the IR
remote is sending, it's an example of using PWM for communication.
Carrier signal:
durations from the remote to the IR detector.
Communication protocol: A communication protocol is a set of rules for devices that have
to exchange electronic messages. Protocols tend to have rules for voltages, the amount of
time signals last, carrier signal frequencies and/or wavelengths, and much more. When two
or more devices follow the rules of a given protocol, they should be able to communicate
and exchange information.
The IR remote uses a 38.5 kHz "carrier signal" to transmit the pulse
Chapter 1: Infrared Remote Communication · Page 5