TD3X ( pi )

[ivconic]

Oh no, i don't have doubts in your schematic, on contrary; i have doubts in my schematic because i am not sure if i connected all the pieces of your schematic properly.
Might be that i misunderstood some points and comments and connected them wrong.
That's why i am asking you to check it, please do focus only on points of connection between pieces of your schematic.
...
Ok, i understand your reasons to use ldr. But that might be a problem for me (and others too) in case we can't obtain the very same one you used.
What would be the closest from optocouplers which we have available in shops, to match your ldr+irled coupler setup?
Also i plan to skip battery check part, the one with led diodes.
Simple reason; to save space and draw smaller pcb, which will fit particular enclosure that i am planing to use.

[sinclairuser]

hi dooley, nice to see your project getting some interest, i looked at your circuit for my own winter project(PI+VLF in the same enclosure), but in the end i went with minipulse for PI but only due to A-already having a board (silverdog), B- size and shape of board and C- positive ground of the MPP.
when i have done this i may give yours a go.

[daverave]

what is the purpose of the opto coupler ????

[Davor]

Proper name is a vactrol, or resistive opto-isolator, a component that is recently regaining its popularity in audio consoles etc.

[Orbit]

Try to do that 2x bc107 ,insert in housing without light !

[daverave]

but what is the purpose of the opto coupler ??does it make the detector more immune to noise and more stability ???

[Old cart]

Main use of an optocoupler is to isolate one part of circuit from another. In this case it keeps small noise voltages from getting into the vco circuit , making it quieter and more stable.
They are normally much slower than direct coupled circuits which also contributes to the smoothness of the response.
My guess is this is one of the main reasons this doctor sounds so nice.

[DOOLEY]

hello all.

davor is absolutely correct,
it's a homemade VACTROL.

it's only purpose is to alter the sound pitch from the audio 555.

the sound channel is one volume, either on or off,
target intensity is indicated by pitch using the homemade vactrol.
it raises the pitch as the target get closer.

as the human ear can detect pitch changes better than volume changes I
did the sound this way to try to portray more target information via sound.

tried many many ways to alter the pitch in a "NICE" sounding way on a 555,
homemade part was the simplest solution.

tried transistor opto-couplers but to be fair they conduct more in one direction than the other when "on"
so waveform doesn't stay 50/50 duty.

yes,
tried 2 x transistors but this also altered duty.

tried 2 opto-couplers in opposite polarity's this also didn't maintain 50/50 duty.

and varying voltage on pin 5 CERTAINLY doesn't maintain 50/50 for nice audio !!

an LDR rated at nominal 25k will work well,
just the cheap ones seam slow,
too slow to keep up with a target passing so the pitch change lags behind.

the "fast" ones out of my bits boxes were the resin encapsulated ones,
domed top ones,
poss 20 years old,

the new "SLOW" ones off ebay were only lightly sealed flat top ones.

poss my bad luck getting "slow" ones.

[DOOLEY]

hello old cart,

yup ,
this is also true,
tiny spikes don't affect audio pitch in a notable way.

[eclipse]

Few optocouplers for consideration:

SFH615AA
http://www.vishay.com/docs/83672/sfh615aa.pdf

SFH610A
http://www.vishay.com/docs/83666/sfh610a.pdf

VO615A
http://www.vishay.com/docs/81753/vo615a.pdf

Probably I'll get couple of to test which works best, thanks Dooley for the tip that not all optocouplers are created equal

[daverave]

do the opto couplers work well with non vco audio with more stable threshold????

[Davor]

Few optocouplers for consideration: ...

None of these are vactrols. If you wish to obtain a vactrol, the easiest way is making your own, as DOOLEY did. Popular ommercial version is a vtl5c3/2 but you'd need those only if you wish to have equal behaviour from several devices, which is not the case here.

[eclipse]

You're right, my mistake. Haven't dealt with opto components yet. Here are options for LDR output optocouplers from Farnell:

http://uk.farnell.com/photocell-ldr-output-optocouplers

[Old cart]

The spec sheet for the VTL5C3 is here.
http://www.alliedelec.com/images/pro...R/70219697.pdf
The key here is that these use a photocell ( not a transistor) that is optically coupled to an LED. This gives a voltage controlled variable resistance.
These have a response time of about <40ms which equates to a time smear of about 40mm at a coil sweep speed of 1 m per second.
Looks like these could be used for this application if you don't want to make your own.

[Old cart]

A couple more comments, you will probably have to adjust VR2 to adapt to any individual VACTROL (LDR). You are looking for one that is about 25K ohm with 1.5 volts applied and is fast, maybe on the order of 10 ms or so. These turn off much slower than they turn on so the target response will show a quicker change as you approach the target. This class of products may become hard to find as they use materials that are being phased out.

The slower version of these might work very well to adjust ground balance on an auto ground balancing PI, but that another whole topic.