pulse density modulation

2 Articles

No DAC? Try PDM

January 6, 2024 by 16 Comments

Ever notice that the ESP32-S3 doesn’t have a digital-to-analog converter? [Chris] did and asserts that he doesn’t care because he can just use the PDM system to get the same result. PDM — pulse density modulation — is similar to PWM and, like PWM, requires a filter that could range from a simple RC network to an active filter. You can see the result in the video below.

There are several ways [Chris] could produce the output he wanted. PWM was one choice, and some example code uses a timer to do PDM. However, that is not very efficient. The other alternative is to use the I2S output. However, this does require a few workarounds.

In particular, the I2S output is always stereo and incorporates a clock output that isn’t needed for this application. [Chris] simply output the same value on both channels and routed the clock to some pins that are normally used for startup options. That means they can’t easily be used for your own inputs, but it’s OK to use them for unimportant outputs.

We always enjoy seeing solutions like this because it can give you ideas for use in your own projects. Of course, this won’t apply to every project where you need a DAC, but it still might give you some ideas.

We have looked at PDM before. You could, too, build your own DAC hardware.

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Automated Shusher Keeps Conference Loudmouths In Line

April 13, 2023 by 9 Comments

Few things are more annoying than being at a conference and having an inconsiderate group conducting a vociferous sidebar that drowns out the speaker. More annoying still is the inevitable shushing; nobody likes being either the shusher or the shushed. So why not take the humans out of the loop and automate the chore of keeping the peace?

Such was the challenge presented to [BotBerg] before a recent conference, who came up with this automated shusher (translation) on short notice. The build is based on the Arduino Nano 33 BLE Sense Deck, a sensor-rich dev board that’s perhaps a little overkill for the job, but hey — you roll with what you’ve got. The board’s MEMS microphone is the sensor used here, which measures the ambient sound pressure level multiple times per second. When the background noise exceeds a potentiometer-set threshold, an MP3 player is triggered to play a sound clip entreating the offenders to pipe down. The whole thing is housed in a playful 3D-printed enclosure shaped like a mouth, which should be sufficient reminder alone to keep yours shut.

This was a quick-and-dirty prototype, of course, and probably could use some refinement. Given the behavior we’ve witnessed at some conferences, we’d say hooking it up to a Nerf turret gun would be a justifiable escalation.