Replies to Minipulse Plus

[Davor]

I was wondering about limiting Tx current. There is a fairly simple way of doing it, and there was a solution by our PiTec that uses continuous adjustment still found here: http://www.tb-electronic.de/pi_tech/...cc_circuit.pdf
I'm expecting some improvement in a sense of separating the leading edge against flyback, and also some noise improvement, but I also wish to hear more about it from first hand experiences, if any.

[mickstv]

I was wondering about limiting Tx current. There is a fairly simple way of doing it, and there was a solution by our PiTec that uses continuous adjustment still found here: www.tb-electronic.de/pi_tech/pulse_cc_circuit.pdf
I'm expecting some improvement in a sense of separating the leading edge against flyback, and also some noise improvement, but I also wish to hear more about it from first hand experiences, if any.

Hi Davor, a simple solution would be to add the circuit I posted link below, only a few components needed.

http://www.geotech1.com/forums/showt...-current-pulse

[6666]

Despite the fact that I've built 2 Minipulse Plus detectors using the Build Document, and Andy (Silverdog) and Dean Sarelius have both completed successful builds, no-one has spotted that one so far.

TP10 doesn't exist in REV-B. That should of course be TP9.
In REV-C, TP10 is the ground probe connection.

I've added a note in the Minipulse thread(s), but will not update either document at this time. Eventually, by REV-D(?) we might get rid of all the errors.

All good, cheers.

[joop]

What are the details of your coil? The timebase on your scope is set to 50us, and the RX signal is still settling. Or perhaps your damping resistor is not the optimum value?

Here is a scope shot of my MPP. Channel 1 is connected to TP1, and channel 2 is connected to TP3. As you can see there is some noise on the signal, but nowhere near as much as your's, and this is running from a bench power supply (which is also noisier than using batteries) and next to two computers, and low-wattage fluorescent lighting. I'm using the original Minipulse (500uH) coil, and you can see that it settles within 25us,

My coil is 330 microHenry with a fairly large diameter: 32 cm. Using the damping resistor that came with the kit. I have been looking at pics of the original mini-pulse, the coil seems a lot smaller. Maybe around 20 cm diameter? I will try a different coil and report back on this.

https://www.ahrps.org/forums/file.ph...name=photo.JPG

[johnandles]

I will try a different coil and report back on this.

https://www.ahrps.org/forums/file.ph...name=photo.JPG

Permission denied...

[joop]

Permission denied...

Me thinks everything on the internet is in the public domain...

[Qiaozhi]

My coil is 330 microHenry with a fairly large diameter: 32 cm. Using the damping resistor that came with the kit. I have been looking at pics of the original mini-pulse, the coil seems a lot smaller. Maybe around 20 cm diameter? I will try a different coil and report back on this.

https://www.ahrps.org/forums/file.ph...name=photo.JPG

What johnandles means is that we cannot view the image in your link. It gives the message "Permission denied: links to files in the forum are only allowed from the forum itself."

The original Minipulse coil is 8" diameter. Also, try moving the coil into different orientations and watch if the noise level changes. It may all be external noise.

[joop]

Ah, excuse my misunderstanding. Okay about the coil George, will report back!

[6666]

From the little bit of testing I have done with a 280uH coil, and looking at tp3, this REV-B preamp looks fast.

[Davor]

Hi Davor, a simple solution would be to add the circuit I posted link below, only a few components needed.

http://www.geotech1.com/forums/showt...-current-pulse

My thought exactly, except that most people are blissfully unaware that there is a pin 7 of NE555 that only sinks current, and thus may come very useful in accelerating MOSFET shutdown.
Here is my attempt on a constant current drive with a snubber. V(n005) is a coil voltage (".step param r list .1 10k" is only acting as a switch)
It is apparent that even with a snubber that nicely shapes the flyback, with shutdown acceleration the voltage gets a bit higher.

[joop]

The original Minipulse coil is 8" diameter. Also, try moving the coil into different orientations and watch if the noise level changes. It may all be external noise.

I have fitted a 470 uH coil with a smaller diameter. Noise has gone down a bit, but not to the expected level. When I move the coil around the noise level changes but it stays at a high level. It might be environment noise. To be sure, I will take the PCB to another place next week to see if it helps.

One thing I noticed: U8 is a TL072 in the kit, the component list has a TL062.

[Qiaozhi]

One thing I noticed: U8 is a TL072 in the kit, the component list has a TL062.

That's not the problem. I've just unplugged the TL062 and replaced it with a TL072, and the performance was exactly the same.

[Silver Dollar]

A TL072 draws more current but has less noise than the TL062.

Davor I have been reading some old threads and am still confused about
the "Flyback" on a PI. Some say make it as large as you can and some
use a snubber to cut it off. Whats your take on that?

Here's the old thread about it;

http://www.geotech1.com/forums/showt...I-Power-Output

[mickstv]

My thought exactly, except that most people are blissfully unaware that there is a pin 7 of NE555 that only sinks current, and thus may come very useful in accelerating MOSFET shutdown.
Here is my attempt on a constant current drive with a snubber. V(n005) is a coil voltage (".step param r list .1 10k" is only acting as a switch)
It is apparent that even with a snubber that nicely shapes the flyback, with shutdown acceleration the voltage gets a bit higher.

Hi Davor, I use a MUR460 and 200v zener for my snubber circuit. The other difference between my circuit and yours, is I have the MUR460 connected directly to the Drain of the Mosfet.

[greylourie]

The puzzle of how to synchronize the TX oscillator with the LT1054 is now solved!

The solution is ridiculously simple. I had a brainwave and connected a 100pF capacitor between the collector of Q2 and U2 pin7.
Now it's synchronized. Yippee!

Before you do the modification, connect scope channel 1 to TP1, and channel 2 to U2 pin2. You will see the two signals are asynchronous.
Then fit the 100pF capacitor and you'll discover the two signals are locked together. Simple really.

I tested for any unexpected side effects, such as the +5V supply dropping out at a higher voltage, but could not see any difference. There was also no discernible difference in the detector's sensitivity, but at least everyone can stop mourning the demise of the sync pulse. I will update the latest (REV-C) Build Document tonight, and post the fix in both the REV-B and REV-C threads.

Hello,

Does it matter what type/which way round we connect the capacitor ?