Replies to Minipulse Plus

[josewashere]

Let me know how you go with that one. I used a TL072

[Davor]

Guess it was "TL072 in place of the N̶E̶5̶5̶3̶2̶" should be TL062 instead. I tried several things with an integrator in sims, and my choice would be LF353 (as mentioned earlier), and also a small addition that I may suggest later on when I try it in practice. There is a looming problem of charge injection spikes passing through to the TL061 with the motion mod. There is nothing to iron them out, and TL061 is certainly not fast enough to fix them with a feedback capacitor. Ergo chatters.

[Qiaozhi]

TL072 in place of the NE5532 shifts the threshold further up the adjustment pot and really smooths out the threshold. The threshold is far more stable and sensitivity is same to maybe a touch less. The chattiness as you advanced the threshold pot past the slow ticking sound is gone!

Interesting!
I'll try that mod later and see if I get the same results.

[Qiaozhi]

In the schematic of Rev C there is a 100pf cap from pin 4 on U2 going to collector of Q2. Is this another mod as it's not on pcb layout.
Also is the addition of the sync cap on pin 7 the only difference in circuit between rev c and rev b?

The sync cap needs to be added on the back of the board.(pin 7, U2)
The 'other' cap (c21) Iam not sure .(pin 4).
Hopefully George will set this right.

Oops, that's a bit of a mystery ... probably the result of some late night working.

C21 in the schematic should not be there! As noticed by CAS, it's not on the PCB, or in figures 3 or 4 of the Build Document. That's another one for the errata list.
C20 is the sync cap, and needs to be added under the PCB. This cap will be added in the next board revision.

Hope that's clear.

[6666]

Has anyone tried using a matched set of 470nf for C13 C14? I had 6 of these on hand but couldn't match two.. Amazing the spread of values 447 to 483nf from same batch.

There is a big spread amongst a hand full of caps I matched 2 @ 467nF but they are not in the board yet.

[johnandles]

I have the rev b board but I was looking at the rev c schematic and see there are 2 extra caps (one on pin 4 and one on pin 7 on U2) as against the rev b schematic

The sync cap needs to be added on the back of the board.(pin 7, U2)
The 'other' cap (c21) Iam not sure .(pin 4).
Hopefully George will set this right.

[6666]

In that case just hold a little bit longer as I have a small update on the way, and I'll see to make it myself. I replaced the Schmitt NANDS with a more common CD4011. I realised that I have a spare gate that calls for making a more controllable Schmitt from a pair of them. A small problem with CD4093 is that the hysteresis voltage is not directly proportional with the supply voltage, and you can't know how large it actually is for a given chip.

Ok holding on.

My NJM2068 chips arrived today will try them asap.

[CAS]

What version board do you have?.
You mean pin 7 on U2? to Q2 collector
that is the sync cap.
The first board has also a link to be added from pin 3 to pin 5 on U2

I have the rev b board but I was looking at the rev c schematic and see there are 2 extra caps (one on pin 4 and one on pin 7 on U2) as against the rev b schematic

[Davor]

Hi Davor, no drama, its all good,
Sorry if you answered me somewhere else but I missed that reply
my questions where more a response to silver dollar's reply #325, sorry for confusion .

I built the time base but could not get it to work properly so pulled it apart, but on retesting the 4017
it tests faulty, and does not cycle correctly, so will build the time base again , thanks for the reply cheers.

In that case just hold a little bit longer as I have a small update on the way, and I'll see to make it myself. I replaced the Schmitt NANDS with a more common CD4011. I realised that I have a spare gate that calls for making a more controllable Schmitt from a pair of them. A small problem with CD4093 is that the hysteresis voltage is not directly proportional with the supply voltage, and you can't know how large it actually is for a given chip.

[johnandles]

In the schematic of Rev C there is a 100pf cap from pin 4 on U2 going to collector of Q2. Is this another mod as it's not on pcb layout.
Also is the addition of the sync cap on pin 7 the only difference in circuit between rev c and rev b?

What version board do you have?.
You mean pin 7 on U2? to Q2 collector
that is the sync cap.
The first board has also a link to be added from pin 3 to pin 5 on U2

[josewashere]

Well guys after a few hours of trying different opamps not much result to report.

Lm4562 in place of the ne5532 gives a tiny bit more sensitivity with a corresponding increase in instability

TL072 in place of the NE5532 shifts the threshold further up the adjustment pot and really smooths out the threshold. The threshold is far more stable and sensitivity is same to maybe a touch less. The chattiness as you advanced the threshold pot past the slow ticking sound is gone!

LF353 in place of the NE5532 is very similar to NE5532

Of course all this was tested in a room full of electronics so in the field the far from interfering sources the LM4562 could be better with its apparent higher gain. Has anyone tried using a matched set of 470nf for C13 C14? I had 6 of these on hand but couldn't match two.. Amazing the spread of values 447 to 483nf from same batch.
I really like this detector and hope to add a GB to it so if anyone has a diagram for one I would be keen to try it

[CAS]

In the schematic of Rev C there is a 100pf cap from pin 4 on U2 going to collector of Q2. Is this another mod as it's not on pcb layout.
Also is the addition of the sync cap on pin 7 the only difference in circuit between rev c and rev b?

[6666]

6666, I'm not ignoring your posts, it is only that your repeated questions kinda confuse me. I answered them already, but well...
For clarity, yes, there are actually 3 time bases. The main one is set by the 555 and it controls the rest of shebang. The Schmitt triggers are responsible for a second time base. I need a time base for samples, and as the samples are mere multiples, the timebase is constant for sample, twice the GB, and EF pulse. The third time base is a bit hidden, as it is the first pulse of a time base which is variable to account for different GB exponents. I designed it to operate as a ratio against the sample duration, and thus the GB setting remains valid for some range of sample durations.

We had a lot of bad weather here, and as my "lab" is a table under the stars, I can make something only if the weather is nice. Trust me, I'm already twitching in expectation to see this thing working.

Hi Davor, no drama, its all good,
Sorry if you answered me somewhere else but I missed that reply
my questions where more a response to silver dollar's reply #325, sorry for confusion .

I built the time base but could not get it to work properly so pulled it apart, but on retesting the 4017
it tests faulty, and does not cycle correctly, so will build the time base again , thanks for the reply cheers.

[multieagle]

Thanks. I knew it must be mentioned somewhere.

[Qiaozhi]

Am looking forward to this as my next project. I have a question regarding coil connections. Perhaps it is mentioned elsewhere in this thread, but have not stumbled across it whilst speed reading through the material. It relates to the three PCB connections. First, am I correct that "Screen" refers to the coil and cable shielding?

Yes.

My coils are constructed with a copper shield. The shield has a wire soldered to the coil ground wire, which is in turn connected to the cable shield. Thus at the PCB there are only two connections: shield to negative and central conductor to positive. Can this type connection be used with the Minipulse? Or must I used a two conductor cable from the coil, with the coil shield connected to the cable shield, then connected to the third (Screen) PCB connection?

That will work fine.
Have a look at Fig.7 (page 13) of the Build Document, and note the wiring for a mono coil. Essentially you connect your shield wire to 0V.
The most flexible way to wire your coil connector is to take one wire from the middle pin of PL2 and connect it to pin 1 on the coil connector, and a separate wire from the middle pin of PL4 to pin 5 of the coil connector. Pin 3 of the coil connector goes to 0V (which is any of the outer pins of either PL2 or PL4). Then, when you wire the coil plug, you can connect 0V (coil shield) to pin 3, and the "hot" wire to both pins 1 and 5 (this is for a mono coil). For a coil with separate TX and RX windings you can connect 0V (coil shield to pin 3), the TX wire to pin 1, and the RX wire to pin 5 (obvously without the short).