Frequently Asked Questions

"ping" resulting in a false readings. Fire them sequentially 65mS apart
A. Yes! We do this all the time on our test robot, firing 8 SRF08's at the same time. They
are facing outwards and fitted around a 15inch diameter circle. The gain is set to
minimum and they are fired using the I2C general call at address 0, and read individually
at their set addresses. Under these circumstances there is no direct interference.
A. Possibly! - Try it, and compare the results with firing them sequentially at 65mS
intervals..
Q. If I change the SRF08/SRF10 I2C address, will it stay at that address next time I
switch on or do I need to set it every time?
A. You only need to set it once and it stays set to the new address - even when you power
up again. The I2C address is stored in EEPROM and stays the same until you deliberately
change it.
Q. If I change the SRF08 Range and Gain registers, will they stay the same the next time
I switch on or do I need to set them every time?
A. Unlike the address, which is permanent, You will need to set the Range and Gain
when you power up again.
Q. Can I change the sonar frequency of 40KHz to something else?
A. No. The frequency must be 40KHz, because that is the only frequency the transducers
will operate at. Also the circuitry is designed to operate at 40KHz so you cannot change
the transducers to other frequency types.
Q. If I reduce the range setting of the SRF08, can I fire the sonar faster?
A. Yes, but be careful. If you fire the sonar and there is nothing in the immediate range,
than on the second firing, you may pick up an echo of the first ping which has only just
arrived from a distant object. The second ranging will falsely interpret this as an echo
from a nearby object. To avoid this, don't fire the sonar more frequently than every 60mS
or so.
Q. My software master I2C code does not read correct data from the SRF08/SRF10, but
its works fine with an I2C EEPROM chip. Why is this?
A. The most likely cause is the master code not waiting for the I2C bus hold. This is
where the slave can hold the SCL line low until it is ready. When the master releases SCL
(remember it's a passive pull-up, not driven high) the slave may still be holding it low.
The master code should then wait until it actually does go high before proceeding.
Q. What is the power output of the ultrasonic burst.
A. On the SRF04, SRF08 and SRF10 its 100-150mW.