PWM Audio for PI Metal Detectors

[Vadim18]

Helo everyone!
Last year i tested posibility to use PWM audio output instead of traditional clasic speaker driver.
The idea was realised on cheap cmos logic like cd4011 and two npn transistors.
As for me PWM audio work better.
From pluses are:
*smoth controled sound
*rich for hi harmonics sound thus more herable in windy weather or at weak signals
*less annoing - no mosqito sound, pulses are variable by width so prowide more harmonics
*negligible power consumtion

From minuses:
*relative complexity and aditional costs

Im try provide circuitry and video tests




How to connect to Surf PI circuitry
https://youtu.be/bnT1PebM31o

[Vadim18]

The only option for Surf PI is to connect circuitry to +5V supply rail, because voltage on this rail stabilized.

[Op04]

This is Super,, Thank you for sharing Mr. Vadim, please upload the sound result we would like to hear, if that's ok.
Regards

[Vadim18]

This is Super,, Thank you for sharing Mr. Vadim, please upload the sound result we would like to hear, if that's ok.
Regards

Sound test https://youtu.be/XjG6DwS9mmQ

[Vadim18]

About mosquito sound problem
In original Surf PI audio pulses are short, about 180us so duty cycle is around 10% and that sounds like mosquito.
For better audio duty cycle must be 50%
On monostable trigger i build pulse stretcher/modulator.
By changing resistor value we can set maximum duty cycle to 50%

50% Duty cycle for 600Hz is (1000/600Hz)/2= 0.833 mS

2,2nF*300k*0.8=528uS 32% with 300k resistor in my video demonstration
2,2nF*470k*0.8=827uS 49% with 470k resistor

So i see better to have second additional potentiometer connected in series with 300k resistor to tune exactly to that most wanted 50% duty cycle.
300k fixed resistor + 220k potentiometer is ok

circuit
video demonstration https://youtu.be/XjG6DwS9mmQ

Other things
I'm not tested feeadback loop option in my circuit so you can avoid it.
Input resistor for DC input in my circuitry might be in range from 22k to 100k (100k is better).
As i mentioned in my video you can set sensitivity from sharp response to smooth response by setting 5k pot (1,8k for 12 Volts)
For Clock input is better to be conneted to pin 4 than to pin 11 (pins for cd4093 ic on SurfPi) so you start audio generation after all SurfPI pulses do its job.

[Op04]

Thank you for enlightenment. So it does decreasing background sound, very useful !! i was pondering hybrid surf done by don-ivica-altair, if this can applied to it hope it will make more silent. Thanks for the video update! Regards

[Vadim18]

The piezo driver in my demo is a muRata PKM34EW with a resonant frequency of 1.1kHz, if you can find one you'll be lucky.

Dont make my mistake - use rubber spacer between piezo and surface you wants to fix to.

That piezo in combo with PWM audio is so loud so it can repel any Zombies near you in deep forest and fields, so you can be 99% protected.

[Op04]

[Op04]

PCB

I hope this useful, pls suggest correction. Thanks Sir Vadim for this project!

[Vadim18]

Thats just fantastic. Thanks for replies and your work Op04, i hope after assembling it will fork for you.
Some minor recomendation - try to use all connection just from one side but not from 2 side (except piezo connector), it will be simplier in future to connect this board. Yo can exclude second ground connection. I added one power filtering resitor.

It will be also better to fill all ground traces from right side by solid poligon, two in series connected diodes may be mounted vertically and connected in air.

[Op04]

Thanks for you comments and for this you create some sort of machine sound, although I'm not try to solder soon I will need this for future. You're right, I will update soon. Regards

[Op04]

PCB update, any suggestion are welcome.

[bernte_one]

Can you upload the sprintLayout file as rar container?

[Op04]

Can you upload the sprintLayout file as rar container?

Hi... Sorry It's not .lay I made using PCB Droid. Hope someone can put into .lay

[Vadim18]

Can you upload the sprintLayout file as rar container?

Not a problem, If anybody still interested i will make layout version.