TD3X ( pi )

[Thomas]

looks like one of the gone for good chips Davor mentioned.

[eclipse]

AD8620 is da bomb downside there is no DIP version.

Added 3 LED low battery status led (green, orange, red) using single diffused GREEN+RED LED. Voltage levels may need some adjustments though,
probably 0.5V higher threshold for all will be better for 4 pack LI-ION needs to be checked with the discharge graphs.


TD3X-mod-v0.7.pdf

[Thomas]

Keeps getting better, you planing on most of it being SMD?, My only reservations about the AD8620 were the 6 nV/√Hz and JFET input.

[DOOLEY]

hello eclipse,

just been checking out the spec of the pre-amp you've got in your schematic,
its input bias is a lot lower than a TL 072.

just thinking,
poss best alter the offset arrangement to be more standard,
just in case.

50k pot to 100k pot,
wiper to the 33k
cw to +8v
and ccw to 0v

this should be sufficient .



oh,
best put an emitter resistor between Q5 and the speaker,
( just to keep a member of the forum happy )
33 ohm should be sufficient for a 1.25w speaker.
100 ohm going to phones.
recently used these values in a recent build.


one thing I would have done differently / better thinking on hind sight.
the earth field adjustment, your VR10.
during testing with a small magnet I was unhappy with the range of adjustment,
didn't seem to reduce the effect of the magnet much.

knowing that a 47k 5% could be somewhere between 44k and 49k,
poss best increase the range of adjustment,
im thinking along the lines of VR10 being a 10k pot and R25 being a 4.7k

and just to be safe matching all 4 x 47k's with a meter first.


still think your supply to the AD8620 will need to be higher than coil input voltage.

hang on ,
just spotted something,
the 4v connections on to R6 AND R8,
they will need to go to the live side of the coil not the 4v rail.

[Old cart]

Eclipse in a design without a separately derived negative supply doesn't the coil drive voltage need to be equal to the center voltage? In this case that is 4 volts. Otherwise you could use a coupling cap in between the coil and the 1st amplifier.

[Davor]

...applied Mad Max change, posted by Davor because [ATTACH]34341[/ATTACH]it uses 1 matched pair. Also added some notes - down left corner.

Mad Max mod needs no matched transistors. Actually those PNP transistors may be just about any PNP laying around
Also the growl trimmer VR12 should be 2k5, as the value from simulation is roughly about mid way.

[Thomas]

"best put an emitter resistor between Q5 and the speaker,
( just to keep a member of the forum happy )"

now this starting to get very interesting, maybe Sean_Goddard will throw in some of his Ideas?

[Teleno]

Mad Max mod needs no matched transistors. Actually those PNP transistors may be just about any PNP laying around

Not quite, emitter degeneration does not work miracles. Try replacing Q4 with differet types in the LTSpice simulation and see what happens. The PNP transistors must be at least the same kind and preferably the same batch.

[Thomas]

I don't think Davor was advocating mixing PNP devices, although if he says it works that way I would believe it. Why the gun slinging for Davor? Seems like Davor and KT315. The 2 biggest contributers of Ideas to the forum draw the most fire? What's the Prob?

[ivconic]

I made one yesterday, finished late at night.
It's been a while since last time that i did pcb manually using thermo foil.
Vactrol i made with ldr and small blue led. Tried with red led too but seems blue led is "softer" in behavior.
I replaced 33k with 100k to cut down voltage&current for blue led diode. I got bit better behavior with 100k.
Ldr's i have dozen, mostly new ones. I even tried "couple" from old vcr. Have tried other solutions too.
F is 1.350kHz, coil is 38cm diameter, 0.33mH, 1.2 ohms. Resistor parallel to coil is 330+390 ohms giving 720 ohms.
All the voltages are in range, with trimmer i used on pcb i can't precisely adjust 8v, but 8.14v. +4v line is giving me 4.12v.
Detector is running smooth and is very sensitive on small items. Much more sensitive than Barracuda and SurfPi.
Also distances in air are fantastic; various coins is detecting from 20 to 40cm in air.
Overall; this detector is success! Bravo Dooley!
There is one bad thing though; Q2 BC337 from your schematic can get very hot if 8 ohms speaker is used and audio is present more than few seconds.
Luckily i am having one 100 ohms speaker and replaced 8 ohms speaker with it. Later i tested it with constant audio and Q2 remains stone cold.
So, i was thinking only to make some modifications there at audio output, so any other 8 ohms speakers later may be used without worries.

[eclipse]

Looking great Ivconic!
How do you always keep your board layout so simple, I mean just a few jumpers here and there on the top side is really cool, especially for first layout.
For the speaker there's a suggestion to add 33R for speaker, 100R for headphones on the audio output transistor, perhaps it can help.
Results are impressive too! Wonder how it will perform with larger (square frame coil) with increased pulse width?!

[Davor]

I don't think Davor was advocating mixing PNP devices, although if he says it works that way I would believe it. Why the gun slinging for Davor? Seems like Davor and KT315. The 2 biggest contributers of Ideas to the forum draw the most fire? What's the Prob?

It works allright. It works even with a transistor diode replaced with a normal diode, and a bit adjustment at the growl trimmer, as per attached picture. Output symmetry gets worse though, and therefore a PNP signal transistor of preferably the same type is advised. Please don't consider the attached circuit as a solution - the price difference between a transistor and a diode is too small to compromise this much.

As for people losing temper... everyone is entitled to a bad day. One must tolerate a blow or two. The thing between Teleno and myself is nothing of that kind, but a bit of good old brainstorming. It is usually beneficial for development of ideas.

[eclipse]

Changes made plus some other additions. I'm a bit confused what to do with the preamp supply voltage, 2.2uF cap added (is this cap needed).

TD3XM-v0.8.pdf

[eclipse]

Keeps getting better, you planing on most of it being SMD?, My only reservations about the AD8620 were the 6 nV/√Hz and JFET input.

AD8620 is a suggestion, can be mounted on SO-8 to DIP-8 adapter. All op amps must be DIP packages for easy swap.
Preamp can be TL072/TL082/TL062/AD712, LF412 (NE5532 perhaps?!).
With SMT->DIP AD8620 can be used; With 2xDIP to 1xDIP adapter single package op amps can be used: 2xOPA627, 2xLF356, 2xLF357, 2xLF411, 2xAD711, etc.

[ivconic]

Looking great Ivconic!
How do you always keep your board layout so simple, I mean just a few jumpers here and there on the top side is really cool, especially for first layout.
For the speaker there's a suggestion to add 33R for speaker, 100R for headphones on the audio output transistor, perhaps it can help.
Results are impressive too! Wonder how it will perform with larger (square frame coil) with increased pulse width?!

On contrary, i feel bit rusty in those things. Haven't draw pcbs for a quite some time.
It can be much better and more optimized. I am planing much better pcb once you establish your final version with all the proven modifications.
But, unfortunately; my general attitude toward this forum has dramatically changed due some subjective and mostly some objective reasons, and that's why i don't have slightest intention to ever again post here some of the things that i done.
Especially not my pcb drawings. Why not especially pcb drawings? For one very simple reason; i did a lot in the past and was very ready and friendly to share here on these forums. Here and nowhere else.
But in meantime i see that some people here are using those draws to make decent production numbers and sell world wide, earning indeed decent money... and not even mentioning my name anywhere, nor even in cases when my contribution was more than just moderate in those projects.
Worse of all; i see others logos and peoples names on those pcbs sold worldwide, pcbs and kit completes.
During all those time i haven't receive no refunds for my part of labor, nor i ever received proposal, asking me to agree, permit etc...
On contrary i am receiving constant bashing and harassing, mockery, limitations and constantly am victim of one sided rules here, ugly name callings, ugly and unpleasant insinuations and many other ugly things from several people from this forum.
That's where my huge disappointment in this forum starts. Especially in moderators attitude.
So... that's why i don't intend to share any of my work here no more.
This time all the credits of course belongs ONLY to Doley, because it is his own intellectual property, 100%.
I just did pretty much trivial job by drawing two versions of pcb for it.
Also i intend to draw maybe few more versions, because i like Doley's project much! My hat down to him!
So... don't ask for pcb drawings, i will share those only with just very few people here that i have trust in.
Cheers!

P.S.
Doley you did SPLENDID job here!
Your only mistake was to decide to share it here.
You should keep it for yourself only and in time to try to make smaller series and sell to those interested.
In time you will understand my words.