I am building a sumo.

I heard that the NXT ultrasensor can get wrong reading due to interference of other nearby ultrasensor, which is a likely scenario.

How can I avoid this?

I also heard that a Guy Ziv has written some NXT-G blocks to avoid this issue (by using I2C read/write blocks to "ping" the US sensor, allowing it to be used in an on-demand fashion).

Does anyone has such ROBOTC equivalent functions?

Thanks.

In my driver suite there's a LEGOUS-driver.h has a function for using the US sensor in single shot mode:

Go check out the driver, you can download it from the link in my signature

- Xander

Thanks alot.

However, I hit some error somehow when I tried to use your drivers. The NXT screen displayed something like "3rd party driver error. You have not set up the sensor port correctly. Please refer to one of the examples.". Pls help. Thanks.

The program is as follows:

----
#pragma config(Sensor, S2, frontSonarSensor, sensorSONAR)
//*!!Code automatically generated by 'ROBOTC' configuration wizard !!*//

#include "../rdpartyrobotcdr-v2.3/drivers/LEGOUS-driver.h"

// main program

task main()
{
// test
/*
if (!USsetSingleMode(frontSonarSensor))
{
writeDebugStreamLine("Error calling USsetSingleMode");
return;
}
*/
int d;

for(;;)
{
d = USreadDist(frontSonarSensor);
writeDebugStreamLine("Distance is %d", d);
nxtDisplayCenteredTextLine(2, "Distance is %d", d);
wait1Msec(100);
}
}

Try this instead:


- Xander

No more error but the reading is always out of range.

The likelihood of actually getting bad readings is not all that great when you run all of the US Sensors at once. You could use some kind of filter to make sure you get only good values. It will greatly simplify your program.

- Xander

I will try again. Wish me luck.

Hi,

I still can't get the program working to read distance using your drivers.
- anything wrong with my program?
- do I need do use with a Sensor Multiplexer?

Thanks.

Regards.

You could try it with the MUX but unfortunately at this moment I don't have time to debug the issue due to other more pressing (non-LEGO related) things. I would just use the normal built-in US driver for now and see if you really do get interference with multiple sensors.

- Xander

Hi,

I looked into LEGOUS-driver.h and suspected the following value is not correctly defined after googling.

#define LEGOUS_I2C_ADDR 0x10 /*!< Lego US I2C address */

So I changed it to

#define LEGOUS_I2C_ADDR 0x02 /*!< Lego US I2C address */

And somehow, the program managed to work.

Regards.

Indeed the address of the Ultrasonic sensor is 0x02, as well as almost all HT sensors (and many other NXT 3rd party devices).

That is a rather stupid bug on my part, my apologies. It will be fixed in the next release. I wrote the drivers but never tested it, they were made for someone else. I guess they never really used them either or they would've bumped into this. I will blame them for this.

- Xander

I fully understand and appreciate your kind effort.

Just for sharing
- I tested using normal lego driver and tried to simulate interference by other ultra sensor. However, I couldn't replicate the interference.
- I tested using your 3rd party driver and tried to use the single shot mode. It worked almost perfectly. However, it always returns the last valid distance reading when it is supposed to return an out of range reading (nothing in front)

I do not have more time and capacity to test further so I chose to use the normal lego driver and pray hard there will not be any interference.

Thanks.

I will take your feedback and improve the driver. I really appreciate the feedback, I wish more people would do that

- Xander