After a few year hiatus I want to restart my interest in hobby electronics.=
  One of the last projects that I never had time to start was a range finde=
r.  I wanted to build a sonar/radar.  I have a 400ST/400SR pair of,  for wa=
nt of a better word, "round thingies with two wires attached."  :)  Here is=
 a datasheet I found on the net, out of many, but basically they all look t=
he same (to me).

http://www.robot-electronics.co.uk/datasheets/t400s16.pdf

I can very easily find examples how to make this work in practice, and I'm =
quite sure that I could do it just copying but not  understanding.  But I w=
ant to work backwards from the datasheet, and this particular one doesn't m=
ake sense to me.

My EE knowledge is in the still-learning phase.  The datasheet is nothing l=
ike I've ever seen, but here are some assumptions and questions that I am t=
hinking of in order to at least try to figure out how to connect them up.

1) It has two leads.  I cannot see in the DS where/how to connect them, but=
 can I assume that one of them is ground?
2) In the case of the transmitter, can I assume that one is ground the othe=
r is some sort of waveform that causes it to make a sonar like sound?  Like=
 a speaker?
3) If so, what sort of signal?  I guess PWM, and I would definitely try tha=
t first.  I see 40Khz in the DS and that seems to point there.
4) Then, for the transmitter, I connect one to ground, another to a PIC pin=
 generating a 40Khz PWM signal.

The transmitter logically seems like a speaker of sorts, but how to connect=
 it up with pieces parts like resistors, transistors, capacitors, etc still=
 alludes me.  But I'm willing to do the work to figure that part out if I h=
ave a hint where to look.

The receiver seems more difficult.

1) I assume one of the 2 pins goes to ground, the other connected to a PIC =
pin.
2) I know that speakers also can generate an electrical pulse when connecte=
d in a certain way.  I think this may be something like that.
3)  Would I also be reading a PWM signal as input?  But "what" tells me the=
 distance?
4) And like the transmitter, what other pieces parts do I need, capacitors,=
 op amps, resistors, etc.

I'm not asking for the fish, just how to go about building a fish catching =
machine.  :)

Thanks as always,
Lindy


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