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Parts for DIY ultrasonic sensor, Difference im ultrasonic transducers and recivers? — Parallax Forums

Parts for DIY ultrasonic sensor, Difference im ultrasonic transducers and recivers?

rwgast_logicdesignrwgast_logicdesign Posts: 1,464
edited 2012-10-30 08:33 in General Discussion
Ok so while shopping for other stuff I ran across this its a 40khz ultrasonic transducer for 50 cents limit 5 I think...

http://www.goldmine-elec-products.com/prodinfo.asp?number=G19090

I have wanted to do my own sonar sensor looking around the net its not to hard and you can get better range with a DIY sensor especially at 40khz over the standar 24khz. This project is down the line but I figure I may grab these now. Here is my question.. for all you guys that know a bit about the ultrasonic stuff. All the DIY plans I see use two transducers one to send and one to recive, but there is also this labeled ultrasonic receiver

http://www.goldmine-elec-products.com/prodinfo.asp?number=G19049

These look more like the sensors on the higher end maxbotix sensors like this http://www.maxbotix.com/Ultrasonic_Sensors/High_Resolution_Sensors.htm so are these just receivers? Is this acually what is on a maxbotix module and why is there only one and not two?

Comments

  • ercoerco Posts: 20,256
    edited 2012-10-29 16:18
    Or buy 6 for $500.00 each... :)

    From my experience, avoid like the plague when they say "Sorry, no other data or specs". You're left holding the bag with bargain parts you'll never use. Doomed to stay in your parts bin. Just barely too good to throw away.

    When you get the whole sensor unit for $2, why bother? You'll never do better than that: http://www.ebay.com/itm/HC-SR04-ultrasonic-sensor-distance-measuring-module-NEW-/270961553818?pt=LH_DefaultDomain_0&hash=item3f1691319a

    http://forums.parallax.com/showthread.php?135899-Four-Buck-Ultrasonic-Sensor&highlight=ultrasonic+sensor
  • rwgast_logicdesignrwgast_logicdesign Posts: 1,464
    edited 2012-10-29 16:40
    ya i decided to go that way looking at how hard it acually is to design a diy ultrasonic. I just wanted better range and saw these guys for 50 cents.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-29 18:28
    $1.98, including shipping? Even with cheap parts and cheaper labor, I don't see how that's even possible. Obviously, they're not taking a loss, unless they're also selling credit card numbers.

    -Phil
  • mindrobotsmindrobots Posts: 6,506
    edited 2012-10-29 18:39
    I've often wondered if there are Chinese government subsidies for shipping to help increase exports.
  • RDL2004RDL2004 Posts: 2,554
    edited 2012-10-29 21:00
    I've said it before, there's something not right about that. Consider that the final part of the trip that those sensors make is in the United States and they are transported by the U.S. Post Office. That service alone that would cost you or me a couple of dollars.
  • Tracy AllenTracy Allen Posts: 6,663
    edited 2012-10-29 22:50
    "why is there only one and not two?"

    You can buy Piezo ultrasonic air transducers that are labeled in pairs as "receiver" and "transmitter", or you can buy single units that are labeled as "tranceivers".

    Here is a typical graph of impedance and phase for a receiver/transmitter pair (Prowave 400ER180/400ET180).
    Screen shot 2012-10-29 at 10.29.41 PM.png

    The transmitter and receiver are tuned differently. At 40kHz, the transmitter impedance (solid blue line) is at its minimum, while the receiver impedance (solid red line) is at its maximum. In that way, maximum power can be driven into the transmitter, while the receiver can generate its maximum voltage. The series and parallel resonant frequencies are about 1kHz apart. This makes the transmitter and receiver curves match up for sound pressure level and sensitivity:
    Screen shot 2012-10-29 at 10.37.49 PM.png

    You can use receiver piezo as a transmitter and vice versa, but you lose the matching that comes with a pair. There are ways to "detune" the resonant frequencies by adding an inductor to the circuit around the piezo, and that can shift or to broaden the resonant frequency.

    A salient difference between the pair as above, and a single "transceiver", is that the latter will be damped, a lower Q factor, so that it does not ring like a bell so long after the excitation is removed. Ringing affects the dead time necessary after transmission, before it is able to function as a receiver. A transceiver data sheet will tell you the ring time a one of its parameters, and that might be 1 or 2 milliseconds. Consider that sound travels 30+ cm in one millisecond.
    Screen shot 2012-10-29 at 10.29.41 PM.png
    408 x 208 - 34K
    Screen shot 2012-10-29 at 10.37.49 PM.png
    399 x 238 - 35K
  • agfaagfa Posts: 295
    edited 2012-10-30 04:54
    Thanks for that expaination, Tracy!

    agfa
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2012-10-30 08:30
    mindrobots wrote: »
    I've often wondered if there are Chinese government subsidies for shipping to help increase exports.

    Someone must be helping with the shipping costs to offset them. If we needed to return one of those sensors to China there is no way we could mail it for that price. It would cost more than $2 in shipping for sure.
  • ercoerco Posts: 20,256
    edited 2012-10-30 08:33
    Don't look a gift sensor manufacturer horse in the mouth!

    Unless they have viruses and spycams built in.
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