Shrinking my ultrasonic levitator

#1

Hi.

At the electronics evening on 25 Nov I demonstrated my version of an ultrasonic levitator.
The original build is here: https://makezine.com/projects/micro-ultrasonic-levitator/
I built the version using an L293D type H-bridge chip and capacitor, rather than the stepper motor driver board.

My goal is to create an open build design using cheap off-the-shelf components, protoboard and a simple laser-cut assembly.
That way, code clubs, STEM clubs and makerspaces could create their own kits for use in electronics classes.

You’ll see that the Arduino function is very simple, and I am hoping I can replace the Arduino with an ATtiny chip. However, I lack the electronics knowledge to even know if this is possible.

I’m hoping someone here could have a quick look at the project and come back with a yes/no/maybe.
If yes or maybe, I’ll continue to explore this at an electronics evening.

Thanks
Brendon

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#2

An attiny85 is plenty powerful enough to create that waveform. Here’s an example using hardware timer 0.

The classic grumbly crowd would suggest a microcontroller is overkill and a 555 timer is more than up the task. Here’s a simple circuit with a few components to mange the task but I think however we make things, the key is getting it done!

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#3

Hi Kyle.

Thanks! I had no idea that a 555 would be sufficient (I knew what a 555 can do, but didn’t make the conceptual jump!). This will be MUCH cheaper and less “wasteful”.

I found an even simpler circuit here: https://circuits-diy.com/ultrasonic-sound-generator-using-555-timer/
However, that circuit doesn’t have a 2N2222 transistor to amplify the signal, and I think I probably need that (since the original build used the L293D to amplify the signal)?

I need to attach 2 transducers. Based on the original build, it looks like I can just attach them in parallel?

Thanks again
Brendon

#4

Hi Brendon,

Yes, I would definitely use a transistor to drive them in parallel. Your previous work seems to validates that approach. I think that consistent frequency is more important than exactly nailing the 40kHz. The only potential issue I can think of is temperature changes will cause the frequency to drift and thus change the optimal distance between transducers.

#5

Hi Brendon,

I’ve always wanted to learn LTSpice so I used this project as motivation! I’ve built up the example posted above and simulated it

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image.png2736×1757 117 KB
You can see 10 peaks over .25ms or 40kHz.

The transducer modeled as a 1k resistor is a very coarse model, here’s a hackaday article about refining it to approximate real world conditions much better. Still useful for poking around however.

Short cuts worth learning:
F2 Component e.g. “npn transistor” -> right click once placed and change it to 2N2222, or “volt” for supply/signal, NE555 for 555, etc
F3 Wire
F4 Create a net label e.g. Enter in +VCC and all same named nets are connected
F5 Delete - drag a box entirely enclosing what you want to delete
F7 Move - drag a box entirely enclosing what you want to move, will not keep things connected
F8 Drag - drag a box entirely enclosing what you want to move, keeping things connected
C Capacitor
R Resistor
…
Rotate: Ctrl+r
Mirror: Ctrl+e

Again, right click any symbol to edit its properties.

Hit simulate and set the duration to .25m (seconds implicit unit), then click on a wire to see the signal.

Here’s the tutorial I followed, only watching the parts with LTSpice visible

#6

Thanks for this!

I had just started loading the circuit into LTSpice myself (but without any success).

I built the circuit on a breadboard, and can at least get a voltage and amperage reading on the output to the transducers.

I found an online calculator for calculating resistor and capacitor values in order to set the output frequency.
https://circuitdigest.com/calculators/555-timer-astable-circuit-calculator
The values in the circuit diagram appear correct.

My goal on Thursday night will be to hook the circuit up to the oscilloscope and look at the results.

I connected the 2 transducers which appeared to work for a short while (high pitched buzzing when I lightly touched them with a thin wire). Shortly after that they went silent, and I cannot get a continuity beep or voltage reading across the terminals. I suspect I have killed them.

The learning continues!

Brendon

#7

How far did you get in modeling?

#8

Did you have a current limit resistor?

#9

I got nowhere with LTSpice - have never used it before.
I’m going to shuffle it slightly up my list of things to learn.

I did have a limiting resistor R4 (2k) between 12V and the transducer.
The challenge is that the transducer is not a discrete component with its own datasheet.
I pulled them off a HC-SR04 ultrasonic sensor to keep costs down (weirdly, the transducers are MUCH more expensive as separate components).

#10

I’ve tracked down a P/N after chasing down a couple schematics from SparkFun. TCT40-16T is the trasmitter (swap the last T for R for the receiver). You can find them super cheap on ebay, Amazon, or direct from China. Amazon seems to like the search better when it’s just “TCT40”.

#11

Great! This will help with working out how I blew them up!

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