Building a Minipulse Plus Rev D

[EasyX]

Hi, I am building a minipulse plus right now. As long as I am working on it I would ask questions here, since I am not to confident in what I am doing.

So far I finished step 2.
Now I get 4.3V for the test. Is that something to concern about? After step one I got -4.97V
Battery voltage is 9.7V at the moment.

Edit: battery dropped down to 7.6V... Probably that's the problem now.

Will continue to work on if I got them charged.

Greetings Isaak.

[Rayjay]

Hi EasyX

Try a set of fresh batteries. If that doesn't do it, recheck Step 2............correct parts, soldering. Step 1 with -4.97 is fine.
Good luck

[EasyX]

I didn't have fresh ones at the moment, sounds crazy but I am on a roadtrip in Australia. 12V soldering iron, sitting in the car and try to get this thing working ��

A different questions: at STEP 5 it says r13/14 = 27R

BUT both sets I ordered just have one 27R.

So now the question is if there is one 27R missing or is it wrong in the documentation?

edit: trivia question.... Would it work to run the detector with the car battery? could be maybe 14V probably that's to high?

[Qiaozhi]

I didn't have fresh ones at the moment, sounds crazy but I am on a roadtrip in Australia. 12V soldering iron, sitting in the car and try to get this thing working ��

A different questions: at STEP 5 it says r13/14 = 27R

BUT both sets I ordered just have one 27R.

So now the question is if there is one 27R missing or is it wrong in the documentation?

edit: trivia question.... Would it work to run the detector with the car battery? could be maybe 14V probably that's to high?

The documentation is correct.
The limiting factor is the LT1054, which has a maximum voltage input of 15V.

[Rayjay]

Hi EasyX,

That's R14/R15 = 27R not R13/14 Be careful

[EasyX]

Thanks for the replies. Yes you are right, I just have a bad memory �� before I put something together I always double-check!

[EasyX]

Just want to say that I finished the soldering and it's working!! For now I just have a really simple coil, but I will build a better one. And so far I have no idea how to do the housing.

[geoscash1]

Just want to say that I finished the soldering and it's working!! For now I just have a really simple coil, but I will build a better one. And so far I have no idea how to do the housing.

Congrats on getting it working.

You can get a nice aluminum project box on ebay for very reasonable $$. a 6x4x2 box will work perfect.

for coils shells, go to Dons site, his coil shells are excellent and you have a few sizes and designs to choose from. I used his clamshell style for my mpp, it is perfect.
https://sites.google.com/site/dbcoilshells/

[Teleno]

I'm currently building the kit at step 3. This is what I've observed:

- Kit delivered with TCL555 instead of NE555. The Tx pulse width read a mere 48us in the scope. After replacement with NE555 the pulse read 58us as it should be.
- Fall time at TP1 is a rather slowish 500ns. Probably not so important since the transient pulse will be 10x that.

[Teleno]

"...LT1054 has been synchronized to the TX oscillator, allowing the sampling integrators to eliminate any switching that is introduced into the receive chain."

Can QiaoZhi elaborate on this?

On the scope the period of the LT1054 is shorter than the Tx period. During the Tx period the LT1054 goes high at the rising edge, then low before Tx is done and remains low for about 30us after Tx is done, then back to the original pattern for the rest of the millisecond.

What's the effect of this?

[aeberbach]

Hey great catch teleno! I built step 3 today also and the 45uS pulse really worried me but I kept going and ended up with a working metal detector. I substituted NE555 in and sure enough, longer pulse. If the TLC part is OK the manual should maybe be updated?

[ODM]

Most manufacturers of CMOS versions of 555 mark them with a "C" somewhere in the part number. The cmos timing is different, but generally the timing is consistent between different manufacturers for bipolar 555, and cmos 555.

One advantage of a cmos 555 over bipolar besides lower current draw is its more tame output stage that doesn't shunt the supply when switching like the bipolar does. Makes for a less noisy VCO.

[Teleno]

Most manufacturers of CMOS versions of 555 mark them with a "C" somewhere in the part number. The cmos timing is different, but generally the timing is consistent between different manufacturers for bipolar 555, and cmos 555.

One advantage of a cmos 555 over bipolar besides lower current draw is its more tame output stage that doesn't shunt the supply when switching like the bipolar does. Makes for a less noisy VCO.

Oh well, thank you Sherlock. Timing is inconsistent between CMOS and bipolar versions.

[ODM]

You're welcome, dear Watson Just wanted to point out the reason for timing differences and part code signifying cmos, when looking for bipolar replacements, NE555 seems to be the most prolific but other bipolar will do. And a reason to still keep those cmos 555s around is the VCO.

If there's no replacement 555s to be had on hand to fix the timing, one could also add a 200-300 ohm series resistor with R7, or replace R7 with a 1.5k.

[Teleno]

QiaoZhi: I believe the inconsistency between TLC555 and NE555 is due to the "unorthodox" connection of the astable, using OUT instead of DISC to charge/discharge the cap. OUT has trouble sourcing current in CMOS (10mA max.)