SURF PI SPEAKER MODIFICATION

[vasileios]

Hi all,

I built two SURF PI metal detectors with components from the local market and PCB' s from SILVERDOG with great success.

I only noticed that the sound was very marginal, so I built this modification that made possible to use an external speaker which gave a big audio output.

I used a PNP BD140 transistor but you can use any medium power with heat sink

Regards

Vasileios

[WM6]

Hi vasileios.

Thanks for your solution. What you mean with "sound was very marginal". That sound is not strong enough?

[6666]

Can you please tell us what type of external speaker did you use for the mod ?

[porkluvr]

I hate to be the one to burst your bubble, but have you compared supply current between the original design and that with your mod?

The original design has a short pulse to activate the speaker... your mod reverses that low duty cycle!

Maybe the difference in supply current will not matter very much to you, but you should still be wary. ow ow ow

[vasileios]

Hi,
this modification simply enhances the audio power output. Any kind of speaker can be used from 4 to 16 OHMS.

There is not any change on the tone or the behavior of the device.

The peak current consumption of this circuit is zero with no tone and 150mA when a tone is present

[vasileios]

I mean small speaker that is used in portable radios

[porkluvr]

Hi,
this modification simply enhances the audio power output. Any kind of speaker can be used from 4 to 16 OHMS.

There is not any change on the tone or the behavior of the device.

The peak current consumption of this circuit is zero with no tone and 150mA when a tone is present

I stand corrected!! Taking another look I see that you use an emitter follower (common collector) configuration that does not reverse the signal. Good going!