TD3X ( pi )

[Achillion]

For my modified MPP I designed an audio stage around the XR2206. This is a monolithic function generator capable fo producing a high quality sine. It's an olden days IC and can still be picked up from ebay quite cheap.
In my configuration I use two Vactrols to get a warm but still very fast response that changes both loudness and frequency. With the MPP the threshold I can tune to a nice quiet low frequency sine. The ADA4898 is the headphone amplifier. (I had ordered a couple of these and plugged one in the circuit but they are actually overkill). The Vactrols can be also be easily obtained.

[Qiaozhi]

For my modified MPP I designed an audio stage around the XR2206.

If you would like to have your completed MPP project featured in the "Hall of Fame" -> Completed Minipulse Plus Projects by Geotech members
please email me some photos and a description of your experiences with the detector, plus any modifications made.

The same goes for anyone else who has a completed an MPP that's not already in the list.

[Teleno]

My point is not in line of what is possible on this blue planet, but what may be found in a first electronics shop you barge in. For many of us Mouser is as close as the Moon, and for the other part there are flat rate "fines" for ever wishing to buy anything there.
For that matter the home made vactrol is immensely better, because it is made from garden variety components, and it gives you opportunity to make it with your bare (bear?) hands. Most of us here are not in mass production, but a hobby.

There is also a matter of obsolescence. The most popular projects here are made from components that are in continuous production for the past 30 years or so. Exclusive or elusive components are perfect for a manufacturer that wishes to defer any attempts of reverse engineering. But a hobbyist is a different animal altogether. Say, OTAs. In 2005 Intersil set the status of vastly popular CA3280 OTAs to obsolete, which made many hobbyist spine shiver.

You can't count on commercial vactrols, but you can make your own. The most of the decent transistor arrays are extinct, and the remaining ones are mostly made of unobtainium.

There are other ways to skin a cat. I suggested you to include emitter degeneration resistors simply to avoid the transistor arrays. So instead of adding a few 100 ohm resistors that you already have, you insist on buying the arrays in Mouser, and wait a fortnight for them to arrive. Duh:

You were complaining about matching the transistors "you already have", something a hobbyst can do in a few minutes with a simple multimeter. No you give me a rap about how I should be making my own components before I can be part of an "elite club" to which you are the doorkeeper!

I do not share your Mad Max approach to hobby electronics. I once tried to make my own MOSFET out of Parmesan cheese but failed. As long as there's Mouser, Conrad etc. with good stocks and excellent choice, I'll use them and encourage others to use them. With or without permission from you. Hell I even dare to use AVR MCUs instead of the 8051.

Anyway here's a version with emitter degeneration that achieves 50% duty cycle at all frequencies to an accuracy better than 4%.





VCO_555.zip

[golfnut]

Nice job,,,, took a look at schematic, the tx is from a 4v rail.

Did you settle on 4v after experiments?

ok,
below is the corrected schematic of the timing,

all sheets have been checked and re-checked for errors,
and all are fine,
what you see is what's in my final built 100% working unit.

[ATTACH]32811[/ATTACH]

the difference between the 2 schematics was an overlooked missing link
between pins 4 and 8 on the first 555.

if anyone has any questions about what does what,
or any particular part of the schematics please feel free to ask.

[Tinkerer]

You could also use: ICL8038 at less than 1US$ a piece, for a perfect sine wave.

[Davor]

Teleno, there is no need for you to lose temper. Your previous circuit was immensely better than those before.
Here is the Mad Max improvement. Control voltage goes from zero, and there is a grawl adjust.

[eclipse]

Modified version, haven't checked for errors, did it on one breath

TD3v2.pdf

Simplified oscillator (used Hammerhead osci with 1x555)
Reduced Mosfet Gate resistor to 10R
IRF740 mosfet, 400uH coil & 680R damping resistor
Coil is connected to battery directly
Added voltage filter caps for Mosfet (low ESR)
Changed preamp op amp with AD712
Added RC filter for preamp op amp
Changed TL062 with AD712 (should work fine without the 1V reference voltage, needs testing if this op amp can't offer improvement), so removed part around 1V reference and the op amp there
Removed low battery check part
Removed low voltage warning
Used proposed by Teleno replacement of LDR-IR parts (using 4 matched transistors chip MPQ6002 but others can be used too, even separate transistors as mentioned by Teleno)
Reduced some electrolytic caps values, instead ALL electrolytics are polymer caps with low ESR < 20mOhm
Removed +8V +4V and used fixed value LDO regulators with minimum external parts, 200-250mA since coil is now connected to battery
Added protection diode for +12V reg (diode)
Added decoupling caps
Changed insulating Mosfet diode with MUR460 (minipulse)
+ will add low battery warning with 3-4 additional parts

** warning don't try this at home ** not tested at all **

[DOOLEY]

hello golfnut,

yes,
settled on 4v for the TX.

as I said on previous post,
noticed I was getting the same detection distance on 4v to TX as I was powering TX with 12v.

and the 4v took less power to do the same job,
so I thought, why waste the energy.


the important thing seemed to be the TX on time,
after doing a distance chart on a copper coin with varying TX on times
it was pretty obvious that 70us was a good compromise on power used and distance.

above 70us TX on time did get more distance,
but cost far more power.

very similar end result to most Pi circuits posted,
( IE : TX 12v with +5 -5 voltages for chips)
I just used TX 4v and chips run on 8v ad 0v.

hello tinkerer,
those ICL 8038's have come down in price then,
remember looking at a project with one of them in it ,
was put off by the price at the time.



.................... teleno,
i'm not even going to google the mosfet made of parmesan cheese !!!!
lol.


or should I ???.................

davor, teleno,
cheers for the input.

think i'll stick to my method,
ok,
not 50% duty,
but close enough and a lot simpler.

[DOOLEY]

hello eclipse,

just been looking over your recent PDF,

your 555 TX, pin 1 isn't going to 0v, you've linked it to pin 5 control.........

if your powering coil direct from UN-REGULATED battery, then pre-amp needs to have a greater supply, not 8v.

IC 7.2 needs a 47k before the - input goes to earth.

ah,
I see you've implemented the audio 555 circuit I saw posted earlier.

oh,
no need for r10, d6 and d9.
as battery alarm not in your circuit.

think that's all I can spot.............

the TD3X is starting to evolve ................

[eclipse]

Thanks Dooley, all updated.
Now when the preamp is powered by 12V I opted for the heavy artillery (AD8620), suppose to be better than OPA627/637
with slew rate of 40-50V in both inverting/noninverting config, 6 nV/√Hz noise, CMRR 95db

TD3X-mod-v0.3.pdf

[DOOLEY]

hello eclipse,

had a run through your latest PDF.


what battery voltage will you be intending to run this on ??

im thinking even if the 12v reg is a low dropout battery voltage will still need to be
above say 14v, maybe more.

so if coil is from batt+ then the pre-amps will need to be fed from a higher supply.
not familiar with your op-amp used,
poss someone can advise.

[eclipse]

Made few changes (polymer caps connected to batt should be 20V, therefore 560uF is max capacity),
applied Mad Max change, posted by Davor because TD3X-mod-v0.4.pdfit uses 1 matched pair. Also added some notes - down left corner.

TD3X-mod-v0.4.pdf

[eclipse]

hello eclipse,

had a run through your latest PDF.


what battery voltage will you be intending to run this on ??

im thinking even if the 12v reg is a low dropout battery voltage will still need to be
above say 14v, maybe more.

so if coil is from batt+ then the pre-amps will need to be fed from a higher supply.
not familiar with your op-amp used,
poss someone can advise.

Hi, there are many 0.1V @100mA dropout voltage regulators (ex. LM2940-12V). Batteries planned are 4x18650 - 3.7V (16.8V - 11V)
so lowest voltage expected at the output of +12V regulator will be 10.8V-10.9V

Update:
Will change the regulator to LM2940IMP-12/NOPB, all voltage regulators will be same package SOT223 to increase coolness factor and it has 100mV dropout at 100mA

[Thomas]

eclipse, Like what you've done, looking good.
Not sure about the AD8620?

[Tinkerer]

ICL 8038

They are considered obsolete lots of old stock being offered cheap.