use a second PWM unit + low pass filter with low cutoff to generate an adjustable DC voltage with which you operate the transistor you use to amplify the signal before it goes into the speaker.To adjust the voltage you're feeding into the speaker, you can take different routes: You can program the period of your PWM, that is, the frequency of the output signal. The other outputs pipe this tone through the resistor ladder via the AND gates.Īrduino doesn't really say which microcontroller specifically, but I think all the Arduinos I'm aware of have a programmable PWM unit, so that you need to spend no CPU on generating the signal at all.įor details on different ways to use a PWM unit, please refer to this answer, but the gist is: This is the solution I had tried out already, but the volume levels are not repeatable from one unit to the next, so I would like to avoid adding a trimmer pot.ĭ13 generates a square wave with the audio tone. I could use one pin to generate the base frequency signal, and have 3 pins available to steer some external circuit to modify the amplitude, like this: My limitation is that while sounding the alarm, the Arduino still needs to to other stuff, so I can't stall it in a complicated routine to generate tones for example by doing some fancy PWM that then gets filtered to deliver a signal with different amplitudes. > The issue is: how to modulate the amplitude of the speaker sound? Generating pulses and using a transistor or IC amplifier to drive the spaker is no trouble. This way I don't generate a loud alarm tone from the start, which can be disturbing in a quiet environment. So when the alarm condition triggers I would generate a low volume beep in the audible range, give the user some time to react, then increase the volume, wait, increase again until the user reacts. For a new project with Arduino I need to generate an alarm tone that needs to increase in amplitude over time if the user doesn't take action.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |