Replies to Minipulse Plus

[6666]

As Davor correctly stated, this is a thermal pad (or thermal relief). The word "thermal" is a clue. When you solder a component to the ground plane (as with the Minipulse Pulse) the heat from the soldering iron will dissipate in the ground plane, and could result in a dry joint. If the connection was made solid, you would need to use a higher power soldering iron, which would most likely damage any sensitive components. However, it is possible to define larger spokes for the thermal pad, but in in this instance it's not really necessary.

Thanks for the explanations.

[migusch]

Having a closer look at the schematic (minipulse+ rev-B) I wonder why synchronisation of LT1054 to the oscillator 555 is made via pin 6 of LT1054 ("Vref") and not via pin 7 ("osc")?

[Davor]

My PCB came

It is very well done, and vias are very professional. I'm impressed.

[Qiaozhi]

Been looking very closely at PCB, top quality as always.
There is one pad I have a question mark against, its PL1, the middle connection to the ground plane
it has 4 tiny tracks , as this is the main power connection, this should be a solid connection
as there is a small chance these tiny tracks could act as fuses in a fault situation.

As Davor correctly stated, this is a thermal pad (or thermal relief). The word "thermal" is a clue. When you solder a component to the ground plane (as with the Minipulse Pulse) the heat from the soldering iron will dissipate in the ground plane, and could result in a dry joint. If the connection was made solid, you would need to use a higher power soldering iron, which would most likely damage any sensitive components. However, it is possible to define larger spokes for the thermal pad, but in in this instance it's not really necessary.

[Davor]

This kind of pad is called a thermal relief as it makes soldering much easier than in case of a solid pad. Make no mistake - this is a sign of a good PCB practice.

[6666]

Been looking very closely at PCB, top quality as always.
There is one pad I have a question mark against, its PL1, the middle connection to the ground plane
it has 4 tiny tracks , as this is the main power connection, this should be a solid connection
as there is a small chance these tiny tracks could act as fuses in a fault situation.

[sinclairuser]

I found a couple of drawings that Eric did and it looks like C13 and C14 should be matched.

yes well spotted 6666, and thanks.

[greylourie]

I found a couple of drawings that Eric did and it looks like C13 and C14 should be matched.

This is a good point and reminder.

[6666]

I found a couple of drawings that Eric did and it looks like C13 and C14 should be matched.

[johnandles]

has anyone started yet?,

Just received PCB today here in Southern OZ...must have been a good South Easterly blowing! very quick.
Collecting parts,then get stuffing....
Cheers
John

[sinclairuser]

has anyone started yet?, i have 5v-, 5v+ and half the components for the next stage, but i'm finding it small and fiddly, its ok i will manage but newbies may struggle, you may want to increase the board size a little to increase trace gaps, just an observation.
i will plug away with this as i intend to fit this board into a 1266x case and handle, its the perfect size for that.

[6666]

Thanks Davor, looking forward to see your ideas.

[Davor]

There is not much to tell right now. First I'll have to adapt some balanced front end that is referenced to a positive rail to enable using it with classic shielded monos. I'm quite happy with my shieldless VLF coil that has Rx in balanced configuration with centre tap. It requires a differential front end, and there is no "wet grass" or any other effect related to poor shielding to behold, yet it has no shield at all, and I can use a classic single ended shielded coil with the very same front end as well. The only downside is the noise performance as the single ended front end has half the noise power than balanced one made with the same components. It is not much of a drawback considering the benefits.
I like to call shieldless coils FKK (Freikörperkultur) a German term for the nudist movement.

[6666]

possible balanced Rx input to avoid shielding.

Please tell us more , thanks.

[Davor]

A few thoughts...
I think I know exactly how to add ground balance to minipulse. Surprisingly it should be fairly simple. I thought of avoiding GB with minipulse, but then again - I'd be using it on some difficult terra rossa terrains, so why not?!
I'm also considering a sort of spectrum spreading add-on for 555 time base that should improve its performance near powerlines. Or not. It may be worth a try.
The EF timeslot effectively turns the integrator into a chopper that partially takes care of 1/f wandering offset effects. TL062 is not particularly bad in 1/f region, but perhaps some quieter op amp could do better in its place.
I'm also considering current limitation at Tx and dual coil configuration with possible balanced Rx input to avoid shielding.