I currently I am building a robot that is about a foot and a half wide
and a foot tall, and I am using two Devantech SRF04 ultrasonic rangers.
The problem is that at a close distance the sensors cannot cover the
whole front of the robot. Has anyone had this problem before, if so how
did you fix it. I thought maybe I could connect a two more transducers
on to the solder joints that connect the main ones. Would this work?
Its just that I don't want to pay fore more circuitry if I don't need
to, and I am running short short on IO Pins also.
So long as you don't make the wires more than a meter long and you can
supply enough current for all the transducers it will work fine. You may
get slightly odd results, however because a received sound wave will
reach one sensor before the other.
Hmmmm. I wonder if it would really work to parallel up a bunch of
ultrasonic emitters -- or did I read the post wrong? I don't know what
the SRF04 transducers use, but my guess is a piezoelectric element,
which looks rather like a capacitor to the driver circuit. Unless
changes are made to the circuit I am doubtful you could connect up two
or more transducers and still get the desired output.
Also, what happens to the multiple wavefronts from the separate
transducers? The receiver transducer is cut to accept a narrow band of
frequencies back, and reject the rest -- helps reduce errors from
Doppler effect, for one thing. Multiple emitters are bound to cause
irregular reflections that will result in some wild readings, I am
There are some omni-directional piezo film ultrasonic transducers, but
so far I haven't seen one of them used in a robotics application. What
folks usually do is use multiple SRF04s (or their ilk), and fire them
sequentially. Parallax has a deal on their SRF04 knockoff, the Ping, at
5 for $100. Or put the sensor(s) on a turret.
If anybody has successfuly paralleled ultrasonic transducers I'd like to
read up on how well it worked.
place the transducers far apart.
As the transducers are almost a point source (aperture is 8 mm,
wavelength = 25 mm), there's no problem to separate them let's say 25 cm
or even more, so just move one of the transducers.
(of course the measured length should be recalibrated and isn't
Thanks for all the ideas. So I started to desolder the transducers but
I found that it looks like the transducers are soldered on both side of
the board, and on one side the joint is under the transducer. so I
can't get it off. Is there a known way to remove them?
Use two soldering irons or a large tip to heat both joints at
once, and/or use solder wick to remove all solder from the joint
But in response to your original query, you can use a reflector
at the end of a box, like a periscope:
| || |
| XD |
where the slot at the open end of the box is as wide as the box is
long (to preserve beam width), you'll have a fairly effective
periscope. Mount it vertically with the open slot facing forwards.
The slot must be at least 10mm across, since the wavelength at 40KHz
is about 7mm.
Ultrasonic waves reflect off moderately hard surfaces like light off
a mirror. Anything harder than cardboard would work well, but for
testing, even a cardboard box would suffice.
You'll have trouble with end-to-end reflections if you do that.
You might get further with sound absorbent material under the
transducers, but you want a coherent wave heading *out* the
slot (not directly back to the sender) and an angled mirror
will be important in achieving that.
thought I would give you an update. So I finally got the transducers
off with a flat head screwdriver and a very hot iron. So I got it
connected up and it worked. though I do not know how, or if they will
interfere with each other because I have not hooked them up pointing
the same direction. But it worked, and I only killed one transducer
(pulled one of it's legs off, and while I was putting it back on I
destroyed it completely)
Thanks for all the help and ideas
Is there a difference between transmitter and receiver transducers?
Also Can I hook them up backwards? I had to get one new transducer (of
course they come in sets) but dose it matted which one I hook up where
and how. I could not find out which pin is + and which is - from the
data sheet. Here is the new ones I got
and here is the ones off the sensor
They can be, just as there are differences between mics and speakers. In
non-OEM transducers I've bought, the elements are identified with a T
and an R, obviously for transmitter and receiver. Looking through the
fine mesh of the transducer I can also see differences in the internal
I've seen them where the metal casing of the transducer is obviously
part of one of the terminals. The other terminal is insulated. I would
gather it's a good idea to make the insulated terminal +, and the other
-, so it can serve as ground. Might help if you mount the transducer in
a metal bracket (which I don't recommend anyway, because of the
potential for HF ringing.)
If one of the terminals is not connected to the case, and there is no
other marking or other polarity identification, then I guess it doesn't
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