Interesting mod to Surf PI for VCO option

[6666]

I found this Surf PI mod in my collection of PI mods.

It gives the option of VCO audio, which could be handy if experimenting with TX PPS.

I dont know where it came from and there is no name on it, but could be useful.

[Waikiki_Sweep]

It is very good idea to let sound works independent from detector frequency. But I think most benefits you will have from increasing of detector frequency. It will give you not only more sensitivity but also faster reaction on target so you can move coil faster without risk to skip some targets. 1-2 kilohertz for Surf PI working on sand beach should be OK. (Not for high mineralization ground) But construction of original Surf PI do not let you hear good sound with such frequency. Now you can modify detector to hear usual sound around 600 hertz or even better, using it with VCO and also run impulses at 1-2 kilohertz. To increase frequency you need to lower R1 resistor from 100K to 50-20K. With higher frequency 2000 hertz or more you will see more power consumption, more heat at MOSFET and dumping resistor and also may be you will need to adjust R28 from 210K to 100-150K to keep order in impulses and samples sequence.

Cheapest way to make VCO in Surf PI was to connect pin 5 of 555 chip with pin 7 of LM358 by resistor or capacitor in the original Surf PI schematic. Such trick will let your detector to change frequency of pulses as well as sound when you hit the target

[Denison]

...
Cheapest way to make VCO in Surf PI was to connect pin 5 of 555 chip with pin 7 of LM358 by resistor or capacitor in the original Surf PI schematic. Such trick will let your detector to change frequency of pulses as well as sound when you hit the target

Could you please show how to do this? Can I just disconnect the C16 from the GND and connect it with pin 7 of LM358 to have a VCO audio? There won't be no losses of any kind?

[sinclairuser]

waikiki did a lot of experimenting with the surf, he used them too, follow his instructions above and try it.
sadly he has not been here for over a year, so just try it and let us know if it works.

[qute1]

This actually works very well very simple and gives a real improvement in audio quality as now tone changes as the target is approached really surprised but i did it and it works just fine!

Could you please show how to do this? Can I just disconnect the C16 from the GND and connect it with pin 7 of LM358 to have a VCO audio? There won't be no losses of any kind?

[6666]

This actually works very well very simple and gives a real improvement in audio quality as now tone changes as the target is approached really surprised but i did it and it works just fine!

Glad that it worked for you, but just to be clear which mod from this thread did you actually do?

[qute1]

Sorry thought i had covered that with the quote.....:

"Cheapest way to make VCO in Surf PI was to connect pin 5 of 555 chip with pin 7 of LM358 by resistor or capacitor in the original Surf PI schematic. Such trick will let your detector to change frequency of pulses as well as sound when you hit the target
Could you please show how to do this? Can I just disconnect the C16 from the GND and connect it with pin 7 of LM358 to have a VCO audio? "

So just the VCO part as i find the surf audio irritating to the extreme "maaaahhhhh" and this simple trick makes it much more palatable to the ear (do ears taste?) depth is fine on my ones (for the things i am searching for no tiny scraps of gold near me not a flower gold hunter on some crap network tv show) with decent coils so not messing with the timings.

[6666]

Ok thanks, like this ?

[qute1]

Just disconnect the C16 from the GND and connect it with pin 7 of LM358 to have a VCO audio

Poor mans vco

[qute1]

This way saves you adding another 555 and four more components when surfpi long board is designed to be compact (only just goes in the waterproof tube on my builds sooo) and if you use headphones anyway there is no need for speaker space on the ones i build either.

[6666]

This way saves you adding another 555 and four more components when surfpi long board is designed to be compact (only just goes in the waterproof tube on my builds sooo) and if you use headphones anyway there is no need for speaker space on the ones i build either.

Have you checked pin 3 to see whats happening after this mod ?

[qute1]

Nope its working and no loss of depth and nothing is over heating etc sooo

[nonkapo]

Have done it but cant find much of a difference in the sound. Will try with aditional timer. Any progress with the modding qute1?

[qute1]

No its done as i said and the difference is that now you have vco sound ie the tone changes pitch the closer the metal is to the coil instead of just NUURRRRRR!!!!

[dime196604]

What is VCO sound?