BandidoIIuMax PCB

[Peter Morf]

Hi Max! Thanx for your info. I will replace R5 ad R6 with lower values next week (or is it better to put more resistance to R65 and R7?).
All components are according to Carls schematic, including MC33178 and TLC2262, not that easy to get.. but I managed =)
I don´t really understand the "set geb using ferrite core (find a point where it's ignored)"...
Anyway.. next week I have some time to spend with this.. I´ll keep you posted ;-)

Regards!
Peter

[Max]

Hi Max! Thanx for your info. I will replace R5 ad R6 with lower values next week (or is it better to put more resistance to R65 and R7?).
All components are according to Carls schematic, including MC33178 and TLC2262, not that easy to get.. but I managed =)
I don´t really understand the "set geb using ferrite core (find a point where it's ignored)"...
Anyway.. next week I have some time to spend with this.. I´ll keep you posted ;-)

Regards!
Peter

Hi Peter,
you have right components: fine.
For resistors I suggest first just modify base resistors, lowering 20% or more, could try also down to 4.7Kohm. I've done and worked ok with a set of components different from originals. You would have a bit more consumption than original, but that's ok.

"I don´t really understand the "set geb using ferrite core (find a point where it's ignored)"... "
very easy: find a ferrite round core (a ferrite stick could be used also) then try to get a geb setting that makes your detector ignore ferrite when e.g. at 4-5cm from coil. You have to set to just ignore it or have only some small detection at few mm from coil. This way you ground balance your detector on work bench and can do other tests without worring that wrong geb setting influence e.g. your disc testing.

Best regards,
Max

PS: cause you have right components you would have right -V rail voltage (-2.4 to -3V) so I suppose you have some leak in capacitors used in voltage converter or other things that makes too low voltage appears there, or you have too current drawn.
Have you measured current drawn by whole circuit ? In normal conditions is really low (around 20 mA).

[Peter Morf]

Hi Max!

Still can't get the voltage right... now its -2.2V, still not enough. I have changed resistors (to lower values), capacitors and even the two diodes. I even disconnected the negative rail from the opamps, still the same.
input is a nice square wave at 5kHz and output from C4 is the same but +0.6v to -4.1V.
I measured aver all current to 18mA.
I use 1N4048 as diodes.. should I change to 1N4007 or any other diode?

1000 thanks for all help

Peter

[kt315]

hi Peter.
you have a drop on transistor Q3 1-1,5 Volts and you do not want to see it.
my suggest, you can do
- multiplier on more stages, for increase of voltage
or
- a converter similar to is used in MD-5012.

[Max]

Hi Max!

Still can't get the voltage right... now its -2.2V, still not enough. I have changed resistors (to lower values), capacitors and even the two diodes. I even disconnected the negative rail from the opamps, still the same.
input is a nice square wave at 5kHz and output from C4 is the same but +0.6v to -4.1V.
I measured aver all current to 18mA.
I use 1N4048 as diodes.. should I change to 1N4007 or any other diode?

1000 thanks for all help

Peter

Hi Peter,
don't know why you get so small voltage there.
You could use shottky diodes (e.g. bat48 ) to get better switching (and more efficient conversion), also caps could have too ESR and could cause losses due to electrolitic solution...

You just need about -2.8 volt to get things start working good.
But -3.2 are much better !

As KT315 said there is the drop on Q3 (about 1volt) that you could cut off of your circuit gaining about -3.2v on -V rail.

You just need pull out of pcb the Q3 , then short collector and emitter pads with a jumper.

It's not a cool solution... but I think you could gain that way your -3.2 volts.

Try then let me know.

Kind regards,
Max

[Peter Morf]

Hi again!

Many thanks for your helpful posts.
I've tried some different cheap caps and diodes and now I'm down to -2.6V... so forst of all, I'll try with low-ESR caps and shottky diodes.
Hopefully I will have these tomorrow.
If this doesnt do the trick then I'll add an extra stage or shortcut Q3.

[Qiaozhi]

Hi again!

Many thanks for your helpful posts.
I've tried some different cheap caps and diodes and now I'm down to -2.6V... so forst of all, I'll try with low-ESR caps and shottky diodes.
Hopefully I will have these tomorrow.
If this doesnt do the trick then I'll add an extra stage or shortcut Q3.

Using this diode pump with the current values will not provide an output of more than about 2.6V. Max's workaround of removing Q3 will get you to about 3.6V.
Here's a SPICE netlist of the circuit, and the waveform results are attached.
V(VNEG) is the output voltage, and V(5) is the voltage across C5.

* Diode pump circuit to generate -5V
.model Q2N3904 NPN(Is=6.734f Xti=3 Eg=1.11 Vaf=74.03 Bf=416.4 Ne=1.259
+ Ise=6.734f Ikf=66.78m Xtb=1.5 Br=.7371 Nc=2 Isc=0 Ikr=0 Rc=1
+ Cjc=3.638p Mjc=.3085 Vjc=.75 Fc=.5 Cje=4.493p Mje=.2593 Vje=.75
+ Tr=239.5n Tf=301.2p Itf=.4 Vtf=4 Xtf=2 Rb=10)
.model Q2N3906 PNP(Is=1.41f Xti=3 Eg=1.11 Vaf=18.7 Bf=180.7 Ne=1.5 Ise=0
+ Ikf=80m Xtb=1.5 Br=4.977 Nc=2 Isc=0 Ikr=0 Rc=2.5 Cjc=9.728p
+ Mjc=.5776 Vjc=.75 Fc=.5 Cje=8.063p Mje=.3677 Vje=.75 Tr=33.42n
+ Tf=179.3p Itf=.4 Vtf=4 Xtf=6 Rb=10)
.model D1N4148 D(IS=0.1P RS=16 CJO=2P TT=12N BV=100 IBV=3.867E-10)
R5 vin 1 10k
R6 vin 2 10k
R65 V5P 1 2.2k
R7 2 0 2.2k
Q1 3 1 V5P Q2N3906
Q2 3 2 0 Q2N3904
C4 3 4 100u
D1 5 4 D1N4148
D2 4 0 D1N4148
C5 0 5 100u
R67 5 6 1k
R68 0 6 10k
Q3 5 6 VNEG Q2N3906
RLOAD VNEG 0 10k
V1 V5P 0 DC 5
V2 VIN 0 PULSE (0 5 100u 10n 10n 100u 200u)
.tran 250u 250m
.probe all
.end

[Peter Morf]

At last! -3.4V =)

Qiaozhi gave me the idea to try and optimize this voltage doubler, so I too made a schematic in PSpice looking for the best components.
Now I use two shottky diodes: BAT86, C4 is now a low-ESR cap, transistors changed to two BC557C and one BC547C... Q3 is still on board, R68 is now 47k. In theory PSpice gets -3.9V but I am satisfied with -3.4V negativ rail and is waiting for my ordered coilhousing, eager to balace and test =)

thanks again for taking your time

[Merc]

Any succesful builders of Morf's PCB

I was considering building this detector with Morf's PCB design. Has anyone been successful yet? Any major problems with the layout?

thanks,
Merc

[chemelec]

I was considering building this detector with Morf's PCB design. Has anyone been successful yet? Any major problems with the layout?

thanks,
Merc

I don't know if his design works or not, But my Split Board design for the Bandido does work.

Gary