how does the bandido IIµ max work

[Stijn]

hi everyone,

im making a tesoro bandido IIµ max for school and i need too know how the elektronics in the detector work .
could someone help me with the schematic cuase i dont understand how it works.
i have fiured out wich part is the oscilator for the Tx coil but the rest i dont understand

thank,
stijn

ps sorry if u have some bad english but im from belgium

[Max]

hi everyone,

im making a tesoro bandido IIµ max for school and i need too know how the elektronics in the detector work .
could someone help me with the schematic cuase i dont understand how it works.
i have fiured out wich part is the oscilator for the Tx coil but the rest i dont understand

thank,
stijn

ps sorry if u have some bad english but im from belgium

Hi Stijn,
I'll try to explain what I understand of it.

[Max]

hi everyone,

im making a tesoro bandido IIµ max for school and i need too know how the elektronics in the detector work .
could someone help me with the schematic cuase i dont understand how it works.
i have fiured out wich part is the oscilator for the Tx coil but the rest i dont understand

thank,
stijn

ps sorry if u have some bad english but im from belgium

Hi Stijn,
I've not much time at the moment but try to explain what I understand of it.
I think that a serious study of this circuit cover too much things...that maybe also a simple
university electronic course can't treat in details.
Many things are for "advanced" ...


Is a VLF/T-R detector that uses IB coils. RX coil signal must be nulled to give good response and
avoid saturation on RX preamp stage.

I refer to Carl's schematic and to active components involved only. It can be studied by blocks:
0. is main oscillator (tx) that drive tx coil, built around T1

1. IC7a (1/2 mc3317 is rx preamp in diff. amplifier configuration ac coupled to other
blocks

2. disc control block ic7b, ic5b is a phase shifter used to control first analog gate
then to give samples to upper disc channel input signal

3. gnd control block ic5a is again phase shifter too used to drive two other analog gates
to feed right samples to second disc channel and all-metal channel

4. and 5. are two disc channels (ic9b, ic10b and ic9a, ic10a) formed by integrators ac coupled
and "filters"...well there are much things to describe here...not so simple

6. is "sum-of-effects-network" (of two channels) stage that uses two comparators (ic8a/b)

7. is main all-metal amplifier/integrator ic6b

8. is feedback block ic6a, used in retune operations and also in motion modes

9. is audio response driver/controller (ic3b)

10. is battery checker (ic3a)

11. is internal clock and sync frequencies generator (ic1, 4024 ripple counter); frequencies are 5KHz, 2.5KHz,1.25KHz, 625Hz

12. is audio stage built around t5 and t6...simply a small power amplifier

13. is voltage regulator for +5volt (+V) (lm2931a)

14. is negative voltage converter built by t3,t4,t7 (not -5volts but say, maximum, -4volts, actually less...)


To be brief (hard to do...I'll don't enter in details in disc/gnd operations) :
Before anything else battery check is performed, during about 3 or 4 seconds...
when 5volt present on +v line stage 0 creates oscillation using colpitts
schema oscillator, then tx coil is tuned to about 10khz with that components.
Part of the sine wave signal generated is feed to IC1 that creates clock/audio signals and
then 5KHz are feed to negative voltage converter, that is a charge pump.
This way two voltages are present +5 and -3 or -4 volts...not so important, so op amps have
differential supply (not symm but it's not important here) referred to GND.
So stage 1 amplifies rx signal...10KHz too (coil is an air core transformer...) and feed
other blocks through analog gates.
Gates control is made by stages 2. and 3. but too long to explain this, just remember that
gate control is based on phase shifts.
DISC pot and GND pot changes phase shifts in their outputs thus giving the opportunity to
cancel out gnd signals (phase shifts due to ground signal) and to discriminate between ferrous
and non ferrous metals --> controlling two channels input signals sampling strategy

You end up with no signal at pin5 ic3, then no sound, with ferrous items...(ideally) and signal, then sound,
for non ferrous. This way it discriminates non-ferrous from ferrous.

In all-metal stage 7 is involved too, as also in disc mode, but what's happen in disc channels means nothing.
If an increase of rx signal is detected you have sound. In manual mode you have dc coupling and so drift exist.
When retune or auto set is performed you have stage 8. came in place , thus negative feedback zeroes
output of main all-metal amplifier...you gain the threshold level.

But here in auto...only motion behaviour is present because feedback tend to cancel out imbalances.
The same happens in disc mode...where only motion type of detection is performed.

This all is because there will be drift if non-motion only...giving not stable threshold
so losing much performance. Bandido uses manual-all-metal (non-motion) just for pinpointing.

Battery checker is really a easy thing...based on charge of c7...comparator...2/3of battery voltage
as "fixed" reference...and is due by note duration and ear of abrupt tone stop...wow
Why they used such a thing ???? I don't know. Maybe to avoid visual indication of battery status.
But it's really boring when you switch on to ear this note every time.

Negative converter is hi-inefficient. Can't give -5...and also -4volts is too optimistic.
For sure...in real bought ones V- is something like -3volts, -3.2, -3.3. But no problems here...op amps work fine
also with +2.5/-2.5 here, so it's enough for good operations with right components.

Anyway, Bandido is a very good circuit. But some aspects let me, still now, confused. Not about the circuit itself...
but why they used some design decisions...

Best regards,
Max

[Stijn]

tnx

thank u for the expliantion its been a great help for my school project

stijn

[sonar]

Wow MAX! Incredible work, fantastic solution. Great work MAX! I have no any questions jeez...

[Stijn]

could someone explain the disc channels

hi,

im stuck with my project.
i was typing out my whole tekst about the bandido im building and i got stuck at the disc channels.(ic9b, ic10b and ic9a, ic10a on carls schematic)
i was wondering if someone could explain it too me.

thanks,
stijn

[Max]

hi,

im stuck with my project.
i was typing out my whole tekst about the bandido im building and i got stuck at the disc channels.(ic9b, ic10b and ic9a, ic10a on carls schematic)
i was wondering if someone could explain it too me.

thanks,
stijn

Hi Stijn,
Can go too much in details.
So I'll describe as simple as I can.

First channel is for disc (ic9b, ic10b).
Second channel is for geb (ground electronic balancing , ic9a and ic10a).
Note that 3rd analog gate is for geb operations too but affect always signal from
ic6b that is related to amplitude of signal from coil and related to both all-metal
and disc modes of operation.
3rd gate uses sync switching generated for 2nd gate (second, or geb, channel) then smoothed
by c18 charge/discharge by R34 - that means you have a small delay between 2nd gating
signal and 3rd one...cause you know cmos analog gates are equals and have same commutation
voltages on the same CD4066 - as in this case.
Delay depends on R34/C18 network. Actually, it's a very small delay.
Back to the cannels 1 and 2,
at both gates output you get a dc level that is related to:
- signal strenght from output of preamplifier (that is the same for bot channels)
- sampling timings and samples width
Width is easy cause you have zero-crossing detectors that gives you from gnd and disc shifters
sections. What's truly important are shifts...then timings.
If you look at last threads about bandido you will find the goodrat's diagrams that gives you
an idea of what happens turning gnd and disc pots on timing (so phase shifts).
I had the same diagrams using goodrat's values for caps (you can find in Gary's revised schematics),
I think these last values are accurate, so I suggest you changing these caps have the same diagrams.
Otherwise you will get, probably, out of phase on geb and disc sections like I had too.
The general idea of bandidoII (and vlf in general).
Having two dc levels to deal with , one for disc metals basing on phase shifts they introduce
in the received signal respect to the osc. signal , and one for geb cancelling meaning a signal
that is in direct relation to ground matrix oxides that produce a phase shift when you near the
coil to the ground (the so called "ground-signal").
So, you need the disc dc level to disc out unwanted metals and geb dc level to set a background
level (a zero reaction point) based on actual ground composition of search field.
Electronically speaking you have just integrators/active filters and an ac amplification network
for both channels. Nothing more.
Diodes are for preventing saturation on IC10a/b. C30/31 are for decoupling. Some inerthia is added
by R46/C39 and mirror components on the other channel. This simplifies stable operations in the
circuit where only fast variations could be detected (rapid imbalances) and slowly variations are
then ignored.
Without these strategy the detector actually could drift a lot and be unstable, so could impossible to use.
That's why all-metal auto and disc are operating mode for search (both motion-type) and all-metal manual
is used only in pinpointing operations...cause you lose the threshold really fast and need a continuos retune.
The trick is on iron response...
The circuit is timed in a way that iron signal in one channel behave as opposite of other channel signal,
where a good metal (gold, silver, brass etc) signal behave as in phase with the other channel signal.
When they hit the sum network (IC8a/b) they give positive response when both are in phase and instead
cancelling out (ideally) when there is iron !
Actually disc control is a control on "how" this phase/out-of-phase behave in the circuit...in a way that
you can always reject iron shifts but then can play with sens for various other metals/alloys.
All this stuff work cause iron and iron-like materials (like cobalt, nickel, etc) have the tendency to
concentrate magnetic field lines where other materials deflects field lines (e.g. copper) or are in the
middle of this behaviour (like some precious metals). Target phase shifts depends on the magnetic properties
of targets , where ground related shifts depends mainly on iron oxides in the matrix.

Well, ideally, of course...cause it's not an exact science (sometimes appears much like blackmagic).

Best regards,
Max

[Stijn]

thanks

thanks again max
u have been a great help for my project

best regards,
stijn

[Stijn]

hi everyone,

i know tis is asking a lot but could someone explain me how the feedback block (ic6a), the battery chekker and the negative voltage convertor work ??
cuase i cant seem too figure them out.

thanks in advance,
stijn

[Stijn]

hi everyone,

i know tis is asking a lot but could someone explain me how the feedback block (ic6a and b), the battery chekker and the negative voltage convertor work ??
cuase i cant seem too figure them out.

thanks in advance,
stijn

[Max]

hi everyone,

i know tis is asking a lot but could someone explain me how the feedback block (ic6a and b), the battery chekker and the negative voltage convertor work ??
cuase i cant seem too figure them out.

thanks in advance,
stijn

Hi,
I'll be short on these points, description by examples:

1. batt checker: you have ic3a as inverting op. amp (gain = 2 , 200/100Kohm) ...on the minus
pin you have always 5V (+v) and on positive pin you have a voltage that is 2/3 of the battery
voltage (e.g. 9V full charged battery gives you 6v on +pin). OK, when you switch on the
detector you get a positive voltage at output of ic3a cause you have 5v on negative pin
and about 6v on positive pin---> (6-5)*2 = +2volt (about) on pin 1 if battery is 9v.
Now, suppose that battery is discharged at e.g. 7volts, you have 2/3 * 7v = 4.66..volts at
+pin and then (4.66-5)*2= -0.68v. The zero is when your battery gives 7.5 volts...cause you
get 5volts on +pin and +5v on -pin...so you get (ideally) zero at pin 1.
What all this stuff mean ??? OK: let's look at audio output...it works ONLY if you give some
positive voltage at base of T5, cause you can get some audio frequency signal by the 4024's
outputs on their negative voltages (look at the diodes at outputs of 4024). So , to have
an audio signal one need having a kind of pull-up network that forces some positive voltage
(at least +0.6v..+0.7v , forward drop on T1 base-emitter junction), and then the sound is
given by negative transients of 4024 outputs, that are even there.
This means that battery checker make you hear output sound when it gives positive voltage at
pin 1 of ic3...that passing thru the 4066 IV gate pull-up the base of T1.
After a while the 10uF capacitor charge thru the 430k resistor and then the control voltage of
the analog gate goes from positive +5 to -V (that is the gnd level of analog gates) thus
interrupting the battery checker signal from interefering with output stage: in practice
it's disconnected from T1 (hi-impedeance state of analog gate).
The "while" is related to the charge rate of 10uF capacitor...to the 430K resistor and to the
5v supply voltage...and is 3-4 seconds to get the gate disconnecting.
In the start and transient stage before commutation the negative lead of capacitor starts from
something 5V and then decrease due to the charging by the resistor. This is not so intuitive
cause one could be familiar with measuring the charge of capacitor from the positive lead...
with resistor connected to the positive lead...thus giving a rising voltage from gnd to vcc.
When the battery is fully charged you ear so for that 3-4 seconds a good and loud tone cause
ic3a gives +2volts or so...that are enough to give a strong tone there.
When the battery discharge...you get weaker sound...or even no sound at all if :
battery voltage < (5+0.3)*3/2 = +7.95 volts cause you get (5.3-5)*2=0.6volt that is the
(ideally) required voltage for T1 to be forward polarized !
You then could get weaker sound or bleping or no sound at all , depending on battery conditions.
Only a good battery gives you a strong , loud tone with no pulsing , bleping etc

2. the feedback block IC6A
well...I need to be short here...OK. It's a feedback block...like the ones you can see in
controls books...NEGATIVE FEEDBACK.
When in auto-tune or retune or disc...that block actually get a feedback to the IC6B amplifier
and that causes IC6B to reach an equilibrium around gnd output level. That's what you need to
get it stabilized around GND level, thus far away saturation...and avoid drifting cause feedback
improves enormously immunity to drift in hi-gain amplifiers. You could get much informations in
your books...I think. Any good controls or automation book has a specified section for negative
proportional feedback systems.
How it works ??? well...when IC6B tends to gives much positive voltage e.g. due to drift or also
to an oveload due to a target the feedback block gives a proportional negative signal that sums
to the input signal of IC6B thus resulting in a proportional control again to the equilibrium.
Equilibrium depends on many factors here...offsets, bias currents, noise, vcc/vee etc etc
so I can treat the topic in details.
Another thing to keep in mind is that you use here TLC2262 that is a LinCMOS opamp from (one of my
favourite companies) TEXAS INSTRUMENTS: means that they are CMOS devices and that's means much , much
more as one could think at first. I mean they have low bias currents...and need much less current
instead of other general purpose op. amps...
E.g. when using retune push-button the feedback block came in place, thus IC6B reach the equilibrium
around GND but THEN ? you leave the push-button and something happens --> the feedback block contiunes
giving a control voltage to the IC6B :
C37 voltage is "trapped" by hi-impedeance input of IC6A, and low bias current of LinCMOS gives you the
time e.g. for pinpointing the target (say 30-60 seconds) but then drift appears and C37 lose its charge
also due to leaks and bias current dissipation...so you need to push again retune !
But without the CMOS op amp. you couldn't get 30-60 seconds of stability after "retune" !
Try it changing IC6 with some other rail-to-rail bipolar op. amp. and you'll notice the difference.
A big difference. Actually the used configuration acts as a kind of sample-and-hold amplifier, where
using bipolars gives you no hold...due to the light faster drop-rate of hold voltage.

3. voltage converter
gives 5Khz from tx-osc-frequency div by 2 (10KHz/2)
it's a charge-pump---> voltage doublers...really easy...something is similar to switching supplies or
DC/DC converters (in this case without inductors).
Diodes act like "automatic" switching devices to close and open paths.

I suggest take a look here:
http://en.wikipedia.org/wiki/Charge_pump
http://www.edacafe.com/books/McGraw_...M_begining.pdf
http://www.powerdesigners.com/InfoWe...converter.shtm

Best regards,
Max

[ApBerg]

Hello Max

Great, you are giving some very good explanation !!!

Thanks !

Also for the other frends on this forum that make this forum very intresting!

Ap

[Stijn]

hi,

wel max u have been a great help for my school project
im finishing my tekst and i will upload it on the froum for the people who are interested in it as soon as i get the corrected version back from my teacher (its writen in dutch so i guess not everyone wil be able to read it)

a big special thanks too everyone on this forum who have posted some very usefull things and who have helped people like me too be able too make the bandido work.

best regards,
stijn

[Stijn]

wel i wanted too upload my project for everyone as i prommised but its too big for the forum (663 KB).

its in dutch but if someone is interested just send me a private message with ur email adress and il mail it too u.

best regards,
stijn

[Qiaozhi]

wel i wanted too upload my project for everyone as i prommised but its too big for the forum (663 KB).

its in dutch but if someone is interested just send me a private message with ur email adress and il mail it too u.

best regards,
stijn

Upload it to www.mytempdir.com (it's FREE) and post the File ID here.