XYZ Interactive Technologies, ZX SparkFun Sensor Datasheet
Introduction
XYZ Interactive Technologies (in conjunction with SparkFun Electronics Inc.) has developed introductory
ZX Sensor Models that can be used for rapid proof of concept or for sensor related applications.
These sensors consist of two transmitter(s) and one receiver mounted on one board that constitutes a
short-range reflective distance measurement solution. Current design utilizes infrared technology.
The sensor may be preprogrammed to operate as a ranging device or as a gesture interface. The
package includes a sensor, a USB to serial board, Mini-B USB cable, and downloadable serial software.
The user can demonstrate simple position detection, distance measurement and basic gestures within
minutes of opening the package.
This sensor includes a UART for demo applications and I2C as a communication protocol for embedded
applications like robotics and toys, or devices that have to communicate directly to a processor.
ZX Sensor
The following describes the ZX sensor. There are two types of the ZX sensor available (as shown). The
ZX sensor is available as versions with 1) Through-Hole parts (TH ZX sensor) which allows sensing
solutions that have longer range because of lensing on the emitter snd receiver, and 2) SMT parts (SMT
ZX sensor) which allows sensing solutions that are more compact and may be hidden under IR
transmissible plastic.
The ZX sensor is designed with the following characteristics:
1. UART at 115200 baud (see UART details below)
2. I2C interface (see I2C details below)
3. Continuous data output at a rate of 50 samples/sec
4. Simultaneous UART/I2C data output
5. 3D object detection in depth and in the periphery
6. On-board gesture detection and output (swipes, hand-push, etc.)
7. Optional on-board pull-down resistors for I2C
8. Support for up to two ZX sensors on one I2C bus
9. Optional I2C ID’s as 20 (unsoldered plug) and 22 (soldered plug)
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The ZX/SP sensor has labeled connections with UART and I2C separated. This makes it easy to connect
ready-made connectors (like the FTDI UART connector) directly to the ZX sensor pins (as shown).
Similarly, the I2C connection pins may connect to any two-wire interface using the ZX sensor as the I2C
slave, and any embedded or external processor as the I2C master.
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Note the labeled connections are shown here– it is important that the FTDI cable goes is connected to
the UART portion of the pin-out. I2C connections are for only the 3 pins on the right, as well as using
VCC and GND connections to power the sensor.
ZX Sensor Pin-out
The ZX sensor board contains two emitters and one receiver module,
to determine the position of a
reflector in the Z X space, and
is powered externally using a 4-pin standard 0.025-inch dip connector.
The following is the pin configuration:
1. Pin 1 : NC
2. pin 2 : Input voltage (5.0 volts DC)
3. Pin 3 : RX for connection to an external UART serial transmitter (TX) line
4. Pin 4 : TX for connection to an external UART serial receiver (RX) line
5. Pin 5 : GND for ground.
6. Pin 6 : GND for ground.
7. Pin 7 : DR (Data Ready) for the I2C interface.
8. Pin 8: CL (or the SCL) clock signal for the I2C interface.
9. Pin 9: DA (or SDA) data signal for the I2C Interface.
The input voltage to the board must be between 4.8 to 5.2 volts maximum, and the voltage is NOT
regulated on the sensor board itself. This was done purposefully to allow the user to apply any power
source from an external board supporting the serial I/O from the receiver board for further control
processing. Currently the RXD line does not support any serial data input to the sensor board. Note that
the sensor can function at lower voltages like 3.3 V but the lower emitter brightness will cause the sensor
to have reduced ranging performance.
X is determined by measuring the differential illumination of the two optical elements (emitter-receiver
pair). When the reflecting object (reflector) is precisely above the sensor, both optical elements are
equally illuminated, thus producing a zero brightness differential. By definition this position is referred to
as X origin, or X = 0. When the reflector is not centered, the receiver gets more reflected light from one
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emitter and less from the other; hence one can determine reflector’s location based on the degree that the
light reception is not balanced.
The Z range is a measure of the direct illumination of both receivers. Accurate Z ranging is possible when
the reflector is positioned directly above the sensing element (or IR receiver).
Output X and Z coordinate values are directly calculated by the sensor and presented to the serial link to
be included in the serial output. See section 6 for how the serial output is displayed in the demo
program. The actual calibrated Range (or Z) value may be calculated using an external serial program
that uses a sensor-output to actual range look-up table, to increase ranging accuracy. Such a table could
use a Linear-Spline calculation (for example) to improve the ranging resolution. The Range value
represents the actual distance as shown in the following geometric representation:
In the current design, the Range value output is limited between zero and +80 cm, designed for “arm’s-
length” use cases where low-power consumption is desired, and where the IR receiver senses little
reflective IR beyond the 80 cm range in this design. The limit is also imposed because the edge of the
sensor’s IR beam creates nonlinear effects when the reflector is partially within the beam directly ahead
of the sensor. Longer range sensors can operate at greater distances but require higher power to achieve
the IR reflectivity.
The reflecting surface can be any surface or object that has reflective properties varying from as little as
18% (i.e. the reflectance of a Kodak grey card) to 100% (i.e. or 95% for white paper).
UART Communication Protocol
Physical Interface:
The sensor reports periodically over an asynchronous serial interface (UART) using the following
configuration:
Baud-rate =115200
Data bits = 8
Parity = None
No Handshaking
Data are reported only when a reflecting object is detected. The data refresh rate is approximately 50
samples per second.
Communication Protocol:
Data are reported as a binary frame with the following format:
Msg. Code
(0xF1 to 0xFF)
Data Payload
-
-
-
Each message frame starts with a Message Code (1 byte) followed by a certain data payload
Each message type is identified by a unique Message Code
All message codes are larger than 0xF0.
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All data bytes are unsigned 8 bit integers smaller or equal than 0xF0 (decimal 240)
Note:
signed data are represented with a 120 bias.
Examples:
0
120
-120
→
→
→
120
240
0
X = -55 is represented as 65
X = 75 is represented as 195
The following messages are reported:
Table 1: Message Types
Message
Code
0xFF
Pen Up
Message
Payload
Size
[bytes]
0
Description
Indicates that the reflector moved out
of range. Mark the end of a data
stream.
Each range is represented by 1
unsigned byte with a range between
0 to 240
X coordinate is represented as a
signed byte with a 120 bias.
Z coordinate is represented as an
unsigned byte between 0 to 240
The first byte represents the gesture
code. The additional byte encode
parameters associated with the
gesture (i.e. speed)
This message is used for sensor type
identification.
1-st byte = sensor type.
2-nd byte = hardware version
3-rd byte = firmware version
0xFE
Ranges
2
0xFA
0xFB
0xFC
X Coordinate
Z Coordinate
Gesture Event
1
1
2
0xF1
ID
3
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