LV-MaxSonar-EZ4 Datasheet

LV-MaxSonar
®
-EZ4
™
Timing Description
LV-MaxSonar
®
-EZ4
™
General Power-Up Instruction
Each time after the LV-MaxSonar
®
-EZ4
™
is powered up, it will calibrate during its first read cycle. The sensor uses this
stored information to range a close object. It is important that objects not be close to the sensor during this calibration
cycle. The best sensitivity is obtained when it is clear for fourteen inches, but good results are common when clear for at
least seven inches. If an object is too close during the calibration cycle, the sensor may then ignore objects at that distance.
The LV-MaxSonar
®
-EZ4
™
does not use the calibration data to temperature compensate for range, but instead to
compensate for the sensor ringdown pattern. If the temperature, humidity, or applied voltage changes during operation, the
sensor may require recalibration to reacquire the ringdown pattern. Unless recalibrated, if the temperature increases, the
sensor is more likely to have false close readings. If the temperature decreases, the sensor is more likely to have reduced up
close sensitivity. To recalibrate the LV-MaxSonar
®
-EZ4
™
, cycle power, then command a read cycle.
250mS after power-up, the LV-MaxSonar
®
-EZ4
™
is ready to accept the RX command. If the RX pin is left open or held
high, the sensor will first run a calibration cycle (49mS), and then it will take a range reading (49mS). After the power up
delay, the first reading will take an additional ~100mS. Subsequent readings will take 49mS. The LV-MaxSonar
®
-EZ4
™
checks the RX pin at the end of every cycle. Range data can be acquired once every 49mS.
Each 49mS period starts by the RX being high or open, after which the LV-MaxSonar
®
-EZ4
™
sends thirteen 42KHz
waves, after which the pulse width pin (PW) is set high. When a target is detected the PW pin is pulled low. The PW pin is
high for up to 37.5mS if no target is detected. The remainder of the 49mS time (less 4.7mS) is spent adjusting the analog
voltage to the correct level. When a long distance is measured immediately after a short distance reading, the analog
voltage may not reach the exact level within one read cycle. During the last 4.7mS, the serial data is sent. The LV-
MaxSonar
®
-EZ4
™
timing is factory calibrated to one percent at five volts, and in use is better than two percent. In addition,
operation at 3.3V typically causes the objects range, to be reported, one to two percent further than actual.
LV-MaxSonar
®
-EZ4
™
Pin Out
Product / specifications subject to change without notice. For more info visit www.maxbotix.com
MaxBotix
®
Inc.
LV-EZ4
™
• Patent 7,679,996 • Copyright 2005 - 2012
Email:
[e-mail]
Web:
www.maxbotix.com
MaxBotix, MaxSonar, EZ2, EZ3 & EZ4 are trademarks of MaxBotix Inc.
GND –
Return for the DC power supply. GND (& Vcc) must be ripple
and noise free for best operation.
+5V –
Vcc – Operates on 2.5V - 5.5V. Recommended current
capability of 3mA for 5V, and 2mA for 3V.
TX –
RX –
This pin is internally pulled high. The EZ4
™
will continually
measure range and output if RX data is left unconnected or held high.
If held low the EZ4
™
will stop ranging. Bring high for 20uS or more to
command a range reading.
AN –
Outputs analog voltage with a scaling factor of (Vcc/512) per
inch. A supply of 5V yields ~9.8mV/in. and 3.3V yields ~6.4mV/in.
The output is buffered and corresponds to the most recent range data.
PW –
This pin outputs a pulse width representation of range. The
distance can be calculated using the scale factor of 147uS per inch.
BW –
LV-MaxSonar
®
-EZ4
™
Circuit
The LV-MaxSonar
®
-EZ4
™
sensor functions using
active components consisting of an LM324, a diode
array, a PIC16F676, together with a variety of
passive components.
When the *BW is open or held low, the TX output delivers
asynchronous serial with an RS232 format, except voltages are 0-Vcc.
The output is an ASCII capital “R”, followed by three ASCII character
digits representing the range in inches up to a maximum of 255,
followed by a carriage return (ASCII 13). The baud rate is 9600, 8 bits,
no parity, with one stop bit. Although the voltage of 0-Vcc is outside
the RS232 standard, most RS232 devices have sufficient margin to read
0-Vcc serial data. If standard voltage level RS232 is desired, invert,
and connect an RS232 converter such as a MAX232. When BW pin is
held high the TX output sends a single pulse, suitable for low noise
chaining. (no serial data).
*Leave open or hold low for serial output on the TX output.
When BW pin is held high the TX output sends a pulse (instead of
serial data), suitable for low noise chaining.
Page
2
PD10009e
MB1040