Replies to Minipulse Plus

[migusch]

[...] I added the missing connection [...] ... and it kills the +5V supply. [...] which unfortunately means we cannot sync the TX osc to the voltage inverter. [...]

I´d like to express my deepest sympathies in respect to the very early death of the syncronisation in MPP. R.I.P. sync! Only the good die young.
I feel somehow guilty. Next time I keep my mouth shut...

[Davor]

Anyway, after a quick repair, I added the missing connection from Q2/R5 to U2 pin 7 ... and it kills the +5V supply.

Most probably +5V should come back if C3 is beefed up to 100u or so. Datasheet shows efficiencies down to 1kHz, and in Surf PI PSU there is an ICL7660, which is basically the same thing, and it uses 220u.

[sinclairuser]

that funny davor, when i was looking at the schematic yesterday i wondered how long it would be before someone tried a 7660s.
do you think the bigger cap will re-impliment the synchronisation?, i liked the idea of that.

[mickstv]

I use a LT1054 as a charge pump in the detector I built and the cap I use is a 220uf (in the Minipulse it's C3). I also use Schottky diodes in the voltage doubler (in the Minipulse it's diodes D1 and D2). Schottky have a lower voltage drop.

[Davor]

Larger capacitor pours more juice. In case of higher frequency and smaller capacitor, it pours less juice more often, so I think it should do. Schottky diodes are a better choice for smaller drop, and in this case their leakage does not matter.
Synchronisation is beneficial for lower noise, so I'd go with sync.

[Qiaozhi]

Most probably +5V should come back if C3 is beefed up to 100u or so. Datasheet shows efficiencies down to 1kHz, and in Surf PI PSU there is an ICL7660, which is basically the same thing, and it uses 220u.

The ICL7660 drops out at a much higher voltage (I think it's around 10.5V) which is why I chose the LT1054. It also seems to generate much less switching noise. If (in the future) we upgrade the MPP to include a micro-controller, it will be possible to synchronize the voltage inverter oscillator at a higher frequency which is harmonically related to the TX pulse rate.

Please feel free to experiment with the current setup and see if you can get the sync working. But but sure to check it over the full range of power supply voltages.

Remember ... the MPP design is my [late Christmas] gift to the Geotech Forum, and you are all welcome to modify the design to meet your own requirements. If/when the design gets updated to include new features, then some of these modification will most likely be added. Like Linus Torvalds with the Linux kernel, I reserve the right to be the final arbitrator on what mods get included.

[Qiaozhi]

I´d like to express my deepest sympathies in respect to the very early death of the syncronisation in MPP. R.I.P. sync! Only the good die young.
I feel somehow guilty. Next time I keep my mouth shut...

Murderer!

Seriously though ... please feel free to find problems and make improvements. Davor is already working on a GB addition, which will be interesting. The design is now open source, and I'm just acting as the project coordinator.

By the way, mistakes are things that happen to people who are doers. The only person who never made a mistake, never made anything.

[Davor]

Fair enough.
I'm considering a few minor mods off the bat...
I'll replace TL062 with LF353 (or TL072) in integrator. TL062 sucks at noise and slew rate. Samples taken there are considerably shorter than the time between pulses, so the noise gets worse for that ratio. Bigger problem are the charge injection pulses due to FETs gating that may require some extra speed, as with fast logic and slow TL062 the inverting side of an integrator is at threat of producing noisy spikes.
I'm also considering BF245B that have lower gate capacitance - for the same reason - and perhaps some gate resistors too.
MC14538 could be replaced by CD4098 that has slower transitions on outputs. Faster logic produces sharper spikes, and we do not need that much speed anyway.
I'll go for a GB timing solution, and slow wired OR logic at output - that'll do.

[sinclairuser]

Fair enough.
I'm considering a few minor mods off the bat...
I'll replace TL062 with LF353 (or TL072) in integrator. TL062 sucks at noise and slew rate. Samples taken there are considerably shorter than the time between pulses, so the noise gets worse for that ratio. Bigger problem are the charge injection pulses due to FETs gating that may require some extra speed, as with fast logic and slow TL062 the inverting side of an integrator is at threat of producing noisy spikes.
I'm also considering BF245B that have lower gate capacitance - for the same reason - and perhaps some gate resistors too.
MC14538 could be replaced by CD4098 that has slower transitions on outputs. Faster logic produces sharper spikes, and we do not need that much speed anyway.
I'll go for a GB timing solution, and slow wired OR logic at output - that'll do.

hi davor, silverdog has included tl072 in the kit instead of 062, you might want to look at the data sheet for the tle2072, i have had great success recently substituting them for 072's in my amps(even upgraded a couple of old ones), there a modern version and totally compatable, side by side the data sheets speak volumes, they are giving them away as samples as direct from ti, the tle2071, and tle2074's are just as good too alot better specs than the old tl072 etc.
http://www.ti.com/lit/ds/symlink/tle2072.pdf

[WM6]

I am a little lost in all this changes, corrections and improvement ideas.

Can someone tell me (with purchased silverdog's Minipulse kit in mind), what are now necessary changes and corrections, regarding Minipulse kit, if any? Will kit works as is or not?

[Qiaozhi]

I am a little lost in all this changes, corrections and improvement ideas.

Can someone tell me (with purchased silverdog's Minipulse kit in mind), what are now necessary changes and corrections, regarding Minipulse kit, if any? Will kit works as is or not?

The Silverdog kit should match the MPP Build Document, and none of the suggested changes by Davor and others are included in the current revision (REV-B). If you construct a kit from Silverdog, then it is guaranteed to work. However, it is possible that some substitutions may occur due to availability, such as replacing the TL062 with a TL072. This will not affect the basic operation of the detector.

[sinclairuser]

I am a little lost in all this changes, corrections and improvement ideas.

Can someone tell me (with purchased silverdog's Minipulse kit in mind), what are now necessary changes and corrections, regarding Minipulse kit, if any? Will kit works as is or not?

the posted project in the build document, and the kit are tested and working 100%.
we are just looking for anything we can do on later revisions, and looking for mods, simpler or better ways of doing the project thats all.

[Dean Sarelius]

I've been looking at the sync problem this evening, and ...

The conclusion of my investigations is that there is no requirement to fit either R5, R6 or Q2.
I will remove these in a future update.

Hi George,
R5, R6 or Q2 suggest this should read R5, R9 or Q2 since removing R6 will remove the 100k preset...!
Also I have just completed building the MPP and the build went very smoothly the only part missing from the Components List is R2 (10R)..!
I plan to run some tests before posting my results within the next few days but so far it appears to be working ok about 30cm to a coin..!

[Davor]

The Silverdog kit should match the MPP Build Document, and none of the suggested changes by Davor and others are included in the current revision (REV-B). If you construct a kit from Silverdog, then it is guaranteed to work. However, it is possible that some substitutions may occur due to availability, such as replacing the TL062 with a TL072. This will not affect the basic operation of the detector.

I'm not considering any mods that would affect the board function, apart from the GB module, and it all is just considering replacements of the project parts with clear upgrades. I'd suggest you to use quality sockets for all ICs, and also use sockets for FETs if you plan to experiment with those.
I'm about to design an add-on board for GB, and its wires will be placed in the respective pin holes on the vacated MC14538 socket(s). So even with GB you can use the existing board as-is.

[Qiaozhi]

Hi George,
R5, R6 or Q2 suggest this should read R5, R9 or Q2 since removing R6 will remove the 100k preset...!
Also I have just completed building the MPP and the build went very smoothly the only part missing from the Components List is R2 (10R)..!
I plan to run some tests before posting my results within the next few days but so far it appears to be working ok about 30cm to a coin..!

You are correct. That was a typo, and should have said R9. In fact, I did update the Minipulse Plus REV-B thread at the same time, and put the correct information there. Unfortunately I posted the wrong info in this thread.

The missing R2 error has been added to the Minipulse Plus REV-B thread. The document will eventually be updated when we move to a REV-C layout.

You seem to getting excellent results with the MPP, and hopefully this will encourage others to follow suit. If you want to send me some photos by email, plus details of your coil, and any test results, etc., I will create a new [locked] thread to display everyone's efforts. The reason for locking the thread is simply to keep it clear of the inevitable "Well done" and "Jolly good effort" sort of posts. As you appear to be the first to create a successful build, you will be top of the list.