Replies to Minipulse Plus

[6666]

After I replaced the blown voltage reg in my MPP Rev B, as I put it back together I took current readings as I went, I hope it may help others and their fault finding.

Please note comments
All readings taken using 13 volts, and without pin5 connected to pin 3 of LT1054, got to do that mod asap.
and no r9,Q2, r5 fitted.

With ALL IC’s removed and all pots and coil, and speaker removed
and only 79L05 operating 2.5 Milliamps.

Now plug in LT1054 8 Milliamps.

Plug in U4 TLC555 10 Milliamps.

Plug in U5 Ne5532 23.2 Milliamps

Plug in U8 TL072 30.2 Milliamps note TL072 as supplied in kit

Plug in BOTH U6 and U7 4538 30.8 Milliamps

Plug in reject pot 50 K 30.8 Milliamps

Plug in coil 64.5 Milliamps. Note this was with my coil at time of test.

Plug in U9 Tl061 68 Milliamps

With everything connected and making tone while detecting metal 76 Milliamps.

Please note I then did another test, I removed all the pots and coil 33.2 Milliamps

[fl_finder]

Thanks for pointing me to the proper link.
It is not clear to me which revision post #149 refers to.
I am building the Rev C Minipulse; do R5, R9, and Q2 need to be installed?
Although there were no specific steps to add R5 and R9, the board looked "wrong" without them.
The components were included with the Rev C kit that I bought earlier this month, sp I put them in.
Also, I have put together a testing sign-off sheet for this project. On step 3, I have been getting a 47 microsecond pulse width at TP1 instead of 58 microsecond.
U2 pin 2 seems to be OK, but not exactly sure what it is supposed to be.
When I get to step 6: TP1 channel 1 trigger, TP5 channel 2, short pins 1/2 or 2/3 on PL3, I don't think I really see what I am supposed to see.
I am using a second-hand Tektronix 2232 100 MHz oscilloscope, and have managed to see most of the waveforms acceptably. However, I never see anything looking like figure 10 in the rev C instruction document.
Thanks for the technical help and for keeping me motivated!

[Qiaozhi]

So close...

It took me 3 weeks to complete my Minipulse Project; I wanted it to be one of the first ten completed projects posted on this forum.

Murphy's Law came into play, and it got toasted, literally.

Although I haven't used a 'scope or chased any "trons" in about 20 years, the knowledge started coming back to me as I assembled my project step-by-step. R5 and R9 were an enigma to me, but I eventually figured them out. And I am now on my second "Fast PI Mono coil" thanks to the excellent article from bbsailor.

Some of my off-board connections were a little loose, so I re-soldered all of them, adding an on-off power switch from a random pre-wired connector from my stash. Although the idea to check battery polarity crossed my mind, it was too much fun soldering and heat shrinking the connections, and I forgot to do it. When I applied power to test the switch, I smelled and heard the sad sound of popcorn popping, and watched as a heat blister appeared on my 555 chip from inside a puff of smoke coming from around it.

Luckily, I did happen to have a spare 555 chip laying around from one of my son's homeschool projects, but there is apparently more circuitry damaged than just the chip.

I have ordered a replacement integrated circuit set for a few dollars, and plan to replace all of them to see if the project can be salvaged.

Otherwise, it might be time for a new project kit.

Here (is my attempt at inserting) a few photos:

[IMG]/Users/Rodney/Pictures/iPhoto Library.photolibrary/Previews/2014/08/30/20140830-101639/Fa9nUugPR1+7m1gyLfqBkw/103_3865.JPG[/IMG]

[IMG]/Users/Rodney/Pictures/iPhoto Library.photolibrary/Previews/2014/08/30/20140830-101639/Z+vdu%CDQlK0RLrZt1LVUQ/103_3868.JPG[/IMG]

Still having fun remembering electronics and still planning on building a PI detector. I am hoping to deliver better performance than store-bought.

Have a look at post #149 (page 6) where I described which parts will fail if you connect the battery the wrong way round.

[fl_finder]

So close...

It took me 3 weeks to complete my Minipulse Project; I wanted it to be one of the first ten completed projects posted on this forum.

Murphy's Law came into play, and it got toasted, literally.

Although I haven't used a 'scope or chased any "trons" in about 20 years, the knowledge started coming back to me as I assembled my project step-by-step. R5 and R9 were an enigma to me, but I eventually figured them out. And I am now on my second "Fast PI Mono coil" thanks to the excellent article from bbsailor.

Some of my off-board connections were a little loose, so I re-soldered all of them, adding an on-off power switch from a random pre-wired connector from my stash. Although the idea to check battery polarity crossed my mind, it was too much fun soldering and heat shrinking the connections, and I forgot to do it. When I applied power to test the switch, I smelled and heard the sad sound of popcorn popping, and watched as a heat blister appeared on my 555 chip from inside a puff of smoke coming from around it.

Luckily, I did happen to have a spare 555 chip laying around from one of my son's homeschool projects, but there is apparently more circuitry damaged than just the chip.

I have ordered a replacement integrated circuit set for a few dollars, and plan to replace all of them to see if the project can be salvaged.

Otherwise, it might be time for a new project kit.

Here (is my attempt at inserting) a few photos:

[IMG]/Users/Rodney/Pictures/iPhoto Library.photolibrary/Previews/2014/08/30/20140830-101639/Fa9nUugPR1+7m1gyLfqBkw/103_3865.JPG[/IMG]

[IMG]/Users/Rodney/Pictures/iPhoto Library.photolibrary/Previews/2014/08/30/20140830-101639/Z+vdu%CDQlK0RLrZt1LVUQ/103_3868.JPG[/IMG]

Still having fun remembering electronics and still planning on building a PI detector. I am hoping to deliver better performance than store-bought.

[Davor]

Well, don't wait on me. I'm itching busy at the moment.

@George, I'm thinking of a reverse polarity protection in form of a BS250 or similar MOSFET. Perhaps it would be a good addition for future builds as well.

[josewashere]

GB is the next thing I am going to tackle on my MPP. Just need to get my head around the theory first but have been looking at Davor's circuit he posted previously. The circuitry is pretty straight forward but I always need to know 'why' things work before I build them.

I'm also hanging out for a GB circuit for my mpp

[CAS]

GB is the next thing I am going to tackle on my MPP. Just need to get my head around the theory first but have been looking at Davor's circuit he posted previously. The circuitry is pretty straight forward but I always need to know 'why' things work before I build them.

[maikl]

OK Davor

[Davor]

Apparently not. I'm too busy at the moment to make my Minipulse tick, so I don't have a platform to try it. I have no idea when I'll be able to put a GB circuit on a PCB and test it. Hopefully soon.

[maikl]

Did someone do ground balance?

[Davor]

You may seek formulas for switching capacitors, but estimation is not that complicated - you simply divide input resistance by the portion of time a switch is closed. It is much easier to figure it out by measurements or simulation though. This integrator is a little bit different from the lot.

[green]

Back to the integrator. Still trying to come up with formulas. Got some that work with the spice model. Not sure if they are correct, but I think they are close. Some scope pictures and a chart for R 22 value for Fc = 10 Hz.

[KingJL]

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.

I believe that Tinkerer did some experiments along these lines... you might want to touch base with him and compare notes... He is a great guy to work with.

[green]

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.

some scope pictures. Same as above except 80usec 0n time

[green]

DD coils are made with a slight overlap of the 2 D sections. The detection zone of the dd is in the overlap area. Ferrous targets provide a negative response in the detection zone and a positive response on either side of the dectection zone. All other targets provide a provide a positive response in the detection zone and a negative response on either side of the zone. So as you are swinging the coil, non-ferrous targets provide an audio beep as the coil crosses the target. A ferrous target provides a beep as you approach the target, goes silent as you cross the target, and provides a beep as you leave the target. I love DD's!

Been trying to discriminate with a PI. For me target direction or ferrous, non ferrous effects the signal during the coil off decay. Including some scope pictures of integrator out for the first sample after delay of coil off. I've been trying to discriminate during coil on time. Integrate a sample near the start and integrate an inverted sample near the end of coil on time (5usec samples, 100usec on time). Sum the two outputs, monitor the sum and adjust the gain on sample 2 for no change for a ferrite core target. Compare the change of sample 1 and corrected sample 2. If sample 1 change is higher the target is non ferrous, if change is lower its ferrous. Could use the sum output for target sensing. Probably need EF samples. Seems to work on the bench. Maybe not on the ground.