Post by thread:Visiting ultrasonics, again...

Well, since the ultrasonic sensor I am trying to build it interfaced to a PIC, its legal to talk about it here, right? OK, I tried a couple of different circuits. To generate the 40KHz signal, I brute forced it with a 40Kc xtal and a 4049. That works fine, good square wave driving (and I can hear it). Rx circuit, not so good. I tried a couple of ways, but in one case my amp turned into a osc (of course), and the other works better (using a 324 quad amp), but the final stages seem dead. Tried the obvious (new amp, etc), but it doesn't appear sensitive enough. I going to get another good analog guy to sit down and see what he can tell me, but just curious what (if any) circuits are proven to work. Even an inexpensive commercial solution is an option now (need to have this thing done by mid-april). I need to have a sense distance of 4 to 6 feet. Comments anyone ? -Harrison Cooper spam_OUThcooperTakeThisOuTes.com

>Well, since the ultrasonic sensor I am trying to build it >interfaced to a PIC, its legal to talk about it here, right? > delete message >-Harrison Cooper > .....hcooperKILLspam@spam@es.com > Download microchip's app note AN597 Implementing Ultrasonic Ranging. this interface requires ONLY 3 pins to connect to the polaroid 6500 module. source code is included in the app note. michael

---------- >Well, since the ultrasonic sensor I am trying to build it >interfaced to a PIC, its legal to talk about it here, right? > >OK, I tried a couple of different circuits. To generate the >40KHz signal, I brute forced it with a 40Kc xtal and a 4049. >That works fine, good square wave driving (and I can hear it). >Rx circuit, not so good. I tried a couple of ways, but in one >case my amp turned into a osc (of course), and the other works >better (using a 324 quad amp), but the final stages seem dead. >Tried the obvious (new amp, etc), but it doesn't appear sensitive >enough. I going to get another good analog guy to sit down and >see what he can tell me, but just curious what (if any) circuits >are proven to work. Even an inexpensive commercial solution is >an option now (need to have this thing done by mid-april). I >need to have a sense distance of 4 to 6 feet. Comments anyone ? > >-Harrison Cooper > hcooperKILLspames.com > Might be that the xducers arn't the same or arn't centered at 40kc's. (never expected to use the term kc again!) Try swapping the xmitter and rec xducers. If that don't work then try a varable osc like a 555 and adjust xmit frequencw until the receiver peeks. If you are using the same xsucer for both xmit and receive then adjust xmit frequency until receiver peeks. And if you are using one xducer, how do you get it to stop osilatting when time to receive without residual oscilations? Bill C.

{Quote hidden}>---------- >>Well, since the ultrasonic sensor I am trying to build it >>interfaced to a PIC, its legal to talk about it here, right? >> >>OK, I tried a couple of different circuits. To generate the >>40KHz signal, I brute forced it with a 40Kc xtal and a 4049. >>That works fine, good square wave driving (and I can hear it). >>Rx circuit, not so good. I tried a couple of ways, but in one >>case my amp turned into a osc (of course), and the other works >>better (using a 324 quad amp), but the final stages seem dead. >>Tried the obvious (new amp, etc), but it doesn't appear sensitive >>enough. I going to get another good analog guy to sit down and >>see what he can tell me, but just curious what (if any) circuits >>are proven to work. Even an inexpensive commercial solution is >>an option now (need to have this thing done by mid-april). I >>need to have a sense distance of 4 to 6 feet. Comments anyone ? >> >>-Harrison Cooper >> .....hcooperKILLspam.....es.com >> An internally-compensated general-purpose opamp like the 324 is generally not suitable for 40 KHz signals, except maybe near unity gain (even then it may not have the slew rate). Try using a high-frequency op-amp like a 318 (or one of the many newer ones), a bipolar transistor amplifier, IF amplifier chip (MC1330 ?) or maybe even a string of CMOS inverter sections biased for linear operation. Also, the Kapton film transdusers as used by Polaroid work similar to condenser microphones: they require a bias of a couple hundred volts DC. In an echo-ranging system, the transducer is charged up with bias by rectifying the transmit pulse so it is biased during the receive phase that immediately follows. Some provision for this would have to be made in a split transducer system which I think is what you are trying. Most likely the piezoelectric types of transducer don't require bias. -Mike

Harrison Cooper wrote: > > Well, since the ultrasonic sensor I am trying to build it > interfaced to a PIC, its legal to talk about it here, right? > > OK, I tried a couple of different circuits. To generate the (more stuff here..) You could try to get your analog guy to sit down and look at what's in the Polaroid unit. Don't make any rash assumptions - it's like the comments found buried in the SS system legacy code ('Subtle!'). I can't really tell you what to do (what I've done belongs to Time Tech) but I can tell you that just 'cause it's simple doesn't mean it's easy. If you look at it right you'll get what you want. Tom Rogers VP - R&D Time Tech, Inc.

Hi ! I'm also currently working on an ultrasonic receiver. > > OK, I tried a couple of different circuits. To generate the > 40KHz signal, I brute forced it with a 40Kc xtal and a 4049. > That works fine, good square wave driving (and I can hear it). ^^^^^^^^^^^^ How can you hear it if it's 40kHz ??? That's impossible...(or u are a bat) > Rx circuit, not so good. I tried a couple of ways, but in one > case my amp turned into a osc (of course), and the other works > better (using a 324 quad amp), but the final stages seem dead. > Tried the obvious (new amp, etc), but it doesn't appear sensitive > enough. I going to get another good analog guy to sit down and You should have at least an amplification of about 5000. In order to get that at 40kHz it's often required to use a couple of OPAMPS...Are you using a NE567 PLL tone decoder ? That's a nice way for detecting the signal after it has been amplified. Please tell me if you get some more information 'cause I also really have to get my projekt done.... ciao, Moritz ----------------------- Moritz von Buttlar Kiel, Northern Germany +49-431-542834 ## CrossPoint v3.02 ##

> of OPAMPS...Are you using a NE567 PLL tone decoder ? That's a > nice way for detecting the signal after it has been amplified. > Please tell me if you get some more information 'cause I also really > have to get my projekt done.... My opinion is that a 567 (in order to be usefull) needs a long acquisition time. This means you have to send several cycles of your ultrasonic signal, limiting the distance you can detect (short ranges can't be detected). If you use a very small capacitor, in order to get a fast responce from 567, then your tone decoder will become useless with virtually no noise immunity. I think simple threshold detection should be enough for your application. Also, have in mind that a LM358 has a gain of about x10 at 40KHz ...! It would be interesting to know how can we make an x5000 amplifier, without of course getting EMI and all other kinds of noise (you know, aliens, UFO's etc :-) Best, Argiris Kranidiotis. -- ____________________________ __________________________________ / /\ / /\ / Argiris A. Kranidiotis _/ /\ / E-mail (InterNet): _/ /\ / University Of Athens / \/ / / \/ / Informatics Department /\ / EraseMEakraspam_OUTTakeThisOuTdi.uoa.gr /\ /___________________________/ / /_________________________________/ / \___________________________\/ \_________________________________\/ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \