Replies to Minipulse Plus

[6666]

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

[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.

[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.

[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.

[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.

[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]

My PCB came

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

[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")?

[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.

[Davor]

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")?

Nice catch
There is a missing connection between a collector of Q2 and a pin7, and it is easily corrected with a piece of wire, like this:

[Qiaozhi]

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")?

Oops! ... This looks like a mistake. I'll check it tonight and confirm.

[sinclairuser]

hi all, i have been designing my coil for this and decided to build a split tx/rx ib style, and its got me thinking, do i need a shield on the tx?, or should i shield both coils?.
also does the +ve shield connection have any considerations?, more over i'm using an old 1266x case, if i employ the foil shield where does it connect?, i suspect i know the answer, but i dont want any mistakes on this.
thanks,
ally.

[Davor]

Shield connection goes to 0V, and you should shield both Tx and Rx.
Foil is not the perfect material for the job though, and if you use it remember to insulate Tx shield from Rx shield, and connect them only in one point to avoid loops.

[Qiaozhi]

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")?

Nice catch
There is a missing connection between a collector of Q2 and a pin7, and it is easily corrected with a piece of wire, like this:

I've been looking at the sync problem this evening, and ...

Firstly, the battery pack I was using to test the MPP was getting low, so I grabbed a fully charged 12V lead-acid battery (7Ah) and connected it via jumper leads. Big mistake! Accidentally got the battery leads reversed and [literally] let the magic smoke out of the -5V regulator (U1). (Doh!) The only other component to R.I.P. was the TX 555 oscillator (U4). At least you now know which components are going to kick the bucket if you reverse the battery leads.

Anyway, after a quick repair, I added the missing connection from Q2/R5 to U2 pin 7 ... and it kills the +5V supply. No doubt this is due to the much lower frequency of the TX oscillator compared to the 20kHz internal oscillator of the LT1054, which unfortunately means we cannot sync the TX osc to the voltage inverter. However, the diode pump circuit of the original Minipulse was also free-running, and it worked just fine. In fact I cannot see any disturbance on the pre-amp output due to switching noise.

The conclusion of my investigations is that there is no requirement to fit either R5, R6 or Q2.
I will remove these in a future update.

[sinclairuser]

Shield connection goes to 0V, and you should shield both Tx and Rx.
Foil is not the perfect material for the job though, and if you use it remember to insulate Tx shield from Rx shield, and connect them only in one point to avoid loops.

thanks davor, thats what i thought about the coil, the foil is in reference to the foil shield in the 1266x case, since i'm using this case i thought it may help with emi, i'll be using graphite as usual.
@ george, thanks, these things are sent to test us.