Electronic – arduino – Ultrasonic signal generation

555arduinosensor

I am busy with a robotic arduino project. I have a 40kHz ultrasonic transducer and receiver. What would be the best way to generate the 40kHz signal to drive the transducer.

I have found two ways to do this:

555 timer
Arduino PWM

I have the following schematic for the 555 timer:

enter image description here

My concerns are related to which of these two will generate the best waveform. I am also concerned that having to switch the Arduino PWM on and off might impact on timing accuracy. Am I missing something or is there a much simpler way to drive the transducer?

Best Answer

If you have an available timer channel, and are running at a fairly fast clock rate either off a crystal or with the calibrated internal oscillator, I'd argue you should at least give using that a solid try before resorting to external circuitry - which you are unlikely to get 1% accuracy out of anyway given that it has a capacitor in it.

You can likely time the return of an internally generated signal as accurately as an externally generated one - at worst, if you are willing to loop the signal back into a different pin and thus directly reach a hardware timer with no interrupt latency in the way.

In terms of other methods, I believe it is possible to drive the transducer using a resonant circuit, which could arguably be the most "simple", however getting an accurate frequency and clean start transition may prove challenging. And if there's an unused timer channel and pin available to drive it anyway, then the argument could be made that an external generator, no matter how "simple" is more complicated to fabricate.

Depending on the properties of your transducer you may still need a transistor or other drive amplifier at lest to get maximum output.

Related Solutions

Electronic – 555 timer as Dual Direction H-bridge driver

You can use an inverter chip connected to your 555 timer output. That way you will get two signals, your normal 555 timer output and an inverted version. It sounds like you can use these two signals for your H-bridge.

555 timer output connected to H-bridge input A and inverter input, inverter output connected to H-bridge input B.

Electronic – arduino – basic arduino question – do I need a 555 timer

It can be done with interrupts. Attach an interrupt to a timer, so that it fires regularly (say once a milisecond), and use that interrupt to pop the next command off the top of a queue (could just be an array).

Your main loop then just adds commands to this array.

A single Arduino has 14 IO lines, so the number of motors you can control depends solely on the number of wires needed for each motor.

There are dedicated stepper motor driver ICs that are much better and simpler than using a 555 timer. The floppy drive will be using one (maybe embedded inside another chip). They usually accept simple up/down step signals and convert them into the proper sequence of pulses.

Edit

Example code, using the Timer1 library:

#include <TimerOne.h>

void test()
{
  digitalWrite(5,HIGH);
  delayMicroseconds(100);
  digitalWrite(5,LOW);
}

void setup()
{
  Timer1.attachInterrupt(&test,100000);
}

void loop()
{
}

This will cause digital pin 5 to go high then low once every 100,000µS - you see there is nothing in the main loop at all. Just replace the two digitalWrite() calls with the code to step your motors once. You do not need to specify any inter-step delay in that part of the code - that delay is set by the value of 100000 in the Timer1.attachInterrupt() function. To change the speed of the steps, change that value.

Best Answer

Related Solutions

Electronic – 555 timer as Dual Direction H-bridge driver

Electronic – arduino – basic arduino question – do I need a 555 timer

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