Not relevant if the VMA306 transducers are both capable of TX AND decreased efficiency is still within parameters.
That's gonna break my bank, right? Is there another way, e.g. a third ultrasonic RX with a simple readout?
Break the bank for a scope? I don't think so. Last week I sold a perfectly good 20meg scope for $40.00. There are lots of them available for less. For your frequencies, almost ANY scope would work.
Hi,
Can you tell us the application that need two ultrasonic pairs to be on different frequencies?
How far apart do you want the frequencies?
If you want to operate both units at the same time, please consider this;
The units are tuned to operate at a particular frequency, in part this is a physical property, so changing frequency may not be possible.
Even if you can move the frequency of operation, if your aim is to operate them at the same time, the Rx may not have the selectivity to block any signal not on its tuned frequency.
This means that it will receive both reflections but not be able to tell which signal came from which Tx.
Obviously I'm a complete noob at everything I am trying here so I really appreciate the patient advice from all of you on this project.
Paul_KD7HB:
Break the bank for a scope? I don't think so. Last week I sold a perfectly good 20meg scope for $40.00. There are lots of them available for less. For your frequencies, almost ANY scope would work.
Paul
jremington:
If you ever find one, please post a link.
Ok, I hear you two. I need an oscilloscope and they are not as expensive as I thought they would be.
A quick Amazon search showed a lot of handheld devices within a reasonable price range but I note that they all require an input.
How do I get the ultrasonic input to measure to the device?
TG, in response to your two questions in order:
There are a few different things I want to try including transmitting two different frequencies to be received to measure distance.
The greatest difference I need is 5 kHz, so each in being able to change frequency by 2.5 KHz in opposite directions is necessary.
TomGeorge:
The units are tuned to operate at a particular frequency, in part this is a physical property, so changing frequency may not be possible.
Right, I hear you, it's also something J mentioned. I also understand how the same physics would prevent the RX from performing optimally. This seems like it will certainly be a problem. I don't want to have amplitude issues across the different frequencies.
So, I could test these small transducers but their specific purpose is not compatible with my experiments. This brings me back to the ideas of using tweeters. I've seen this pair which have a range of 4-40 KHz.
jremington:
… how you will generate the frequencies of interest, and drive the transducer.
I'm hoping to be able to use a DDS signal generator that can go up to 40 MHz apparently. The AD9850.
The Arduino can generate any frequency of interest in that range. I recommend to use Timer1, which can effectively place 10VAC on the emitter, by alternating signals on two pins.
I'm unclear on how you propose to measure range between sensors is supposed to work, but this thread documents my reasonably successful experiment in one-way ultrasonic ranging synced with a radio link: Communication Between 2 Ultrasonic Sensors - Project Guidance - Arduino Forum. Also worth noting that the waveforms in post 20 of that link were done with a very inexpensive logic analyzer (Salae clone) and Sigrok open source software.
Informative, but far too long video tearing down and characterizing the transducers in the HC-SR04 rangefinder.
The 40 kHz resonance is indeed pretty sharp.
jremington:
The Arduino can generate any frequency of interest in that range.
Right. I actually discovered the arduino-pwm-frequency-library after purchasing the AD9850. I will also check out Timer 1 as you recommend... looks like I have a lot more to learn on the programming side.
Good find with the video, that rules out the HC-SR04.
So the questions (5 & 6 above) remain regarding the oscilloscope, and whether the XTC PT-1 Piezo Tweeters Pair will do the trick.
Again, I am grateful for all your suggestions and wisdom.
