At 07:16 PM 11/11/97 -0500, Sean Breheny wrote:
>At 01:19 PM 11/11/97 -0800, you wrote:
>>Does anyone want to volunteer some programming expertise and development
>time?
>> Anyone? Anyone?
>>
>> - Rick "Bueller?" Dickinson
>
>Rick,
>
>I love your idea and I was actually working on a simpler sonar-ranging
>device before this idea got introduced as a thread here. I am mainly
>developing the best actual RX and TX circuits as well as what is the best
>format for the sonar pings ( # of pulses, null period to avoid transmitted
>vibration detection, etc. ). I have only been working on it for a few days,
>so far I have a very simple circuit which seems to have very little problem
>actually receiving the signal. I am mainly ironing out the timing issues
>and digital detection method (I am currently using a PLL, but this is
>having trouble locking reliably on only 40 cycles, which I thought might
>happen, so I am moving from a PLL to a comparator clipping/direct PIC
>detection method). I would like to help, not sure how much time I can
>contribute, but I will contribute any major advances that I have. I have
>two questions, what type of maximum range do you want this to handle and
>what will be the accoustics of the areas where you envision it being used?
>This is tough to implement >10meters range when indoors because stray
>reflections are detected.
>
Sean,

I was actually thinking of simply counting on the transducer's own resonance to
 filter things down to just the 40 KHz pulse, and using a couple of op-amps to
 boost the 40 KHz echo signal to the point that it clips and is detectable by
 the PIC.  It sounds like exactly what you are doing.

Are you using the Murata transducers from All Electronics?  Those seem to be
 cheap and readily available, so I was planning on using those.

As far as transmit goes, I was thinking of using a simple FET or BJT amplifier
 stage as follows:
                     Vcc
                      |
                      >
                      < Rc
                      >      C1
                      |____||____
     |             | /     ||    |
PIC  |      Rb     |/            |
Port |----/\/\/----|   Q1        [<   Transducer
Pin  |             |\            |
     |             | X           |
                      |          |
                      |          |
                      V Gnd      V Gnd

What sort of drive circuitry had you planned on using?

 - Rick
---
 You can help design a Serial Sonar Unit for model robots!
  Vist http://www.notesguy.com/notesguy for details, or
   send mail to Rick Dickinson at rtd@notesguy.com