Lego NXT Ultrasonic

The Lego Mindstorms NXT ultrasonic sensor can be used to measure distances and may be connected to a PICAXE using an I2C bus and controlled by appropriate PICAXE I2C commands.

LEGO and MINDSTORMS are registered trademarks of the LEGO Group. I2C is a registered trademark of Philips Semiconductors Corporation.

Related Commands:

Using the Lego NXT Ultrasound Sensor

This is a sample program for the Lego NXT Ultrasound Sensor (part 9846) using the AXE216 i2c Explorer Kit with a PICAXE-20X2.
Please note - This sensor is much more difficult than other Lego sensors to use.

You must provide both 9V and 5V supplies .

Also i2c needs to be 'hacked' due to a feature in the ultrasonic i2c firmware which makes it non-compliant with the industry standard i2c protocol.

SRF005

Code Example:

#picaxe 20x2
#no_table

; **** AXE216 i2c Experimenter Board Setup ****
; J1	External Power	Fitted (4.5V)
; J2	SCL Pullup		Not fitted (pullup is in sensor)
; J3	SDA Pullup		Not fitted (pullup is in sensor)
; H2	9V Power		Fitted (9V)

; Lego Ultrasonic Sensor 
 
symbol distance = b0			; distance in cm

; Wires on NXT jack plug.
; Wire colours may vary. Pin 1 is always end nearest latch.
; 1 White	+9V
; 2 Black	0V
; 3 Red		0V
; 4 Green	+5V
; 5 Yellow	SCL
; 6 Blue	SDA
; Do not use i2c pullup resistor - already provided within sensor.
	
init:	;Slave address is $02
	hi2csetup i2cmaster, $02, i2cslow, i2cbyte

	hi2cout $41,($02)		; continuous mode
	pause 100

main:	; read values

	; This single line should work:
	; hi2cin $42,(distance)
	; but does not as dodgy firmware in ultrasonic sensor

	; therefore here is the workaround

	hi2cout ($42)		; address $42
	low B.7			; fake an extra pulse
	input B.7		; back to input
	hi2cin  (distance)	; read distance
	
	debug			; debug display
	pause 1000		; wait 1 second then loop

	goto main

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