short on VBAT? another board another ailment 130mA currents

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Re: short on VBAT? another board another ailment 130mA currents

Post by RogerClark » Sat Dec 09, 2017 7:52 pm

The crystal is probably working because of parasitic capacitance; but it’s unlikely to be as much capacitance as would be ideal

I would run a small wire from GND, under the board and perhaps hand solder some 1206 SMD caps to the underside of the board.
1206 SMD parts are not impossible to hand solder.

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Re: short on VBAT? another board another ailment 130mA currents

Post by ag123 » Sun Dec 10, 2017 3:31 pm

i'm actually thiinking in terms of doing a gimmick capacitor like this post from pito
Pito wrote:
Wed May 03, 2017 10:05 am
Basically it does not matter what kind of 32kHz resonator you use - it matters how you tune the frequency exactly.
The difference 12.5pF vs. 6pF mostly affects the frequency (because the oscillator inside the chip assumes a specific capacity of the resonator). These ceramic fork 32kHz resonators are made such they have the temperature coef zero around wrist temperature.
In each case you have to tune - the best way is to use a gimmick capacitor (about 3-5mm of twisted 0.2mm magnet wire) at the input side of the oscillator against the ground (wired in parallel to the ceramic capacitor). By selecting the right ceramic cap and cutting off the gimmick wire (by tenths of mm) you can tune the frequency precisely.
1cm of gimmick cap is about 10pF.
1pF makes a difference of seconds/month.
The shorter the gimmick cap the faster the clock.
Not to scale!
unfortunately a baite MM has basically 2 precious ground pins for connection, and i'm yet to figure out how to fit them neatly on a MM/BP, i'd imagine if i use thin magnet wires (awg >30 i.e. thinner than 0.25mm) i'd be able to share the same hole / slot for the crystal contacts. however, for ground pins i'm yet to figure out a convenient way to fit things in neatly
ideally to fit the crystal and the (gimmick) capacitors contraption so that it'd fit nicely as if it is part of the board, but i guess it won't be easy to work that out

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Re: short on VBAT? another board another ailment 130mA currents

Post by gilhad » Sun Dec 10, 2017 8:57 pm

Just observation - I am used to push normal pin (from pin-header) and one 0.2mm enameled wire in to the same hole (either the same way or opposite way, as just better suits me) and solder it (on common universal PCBs to make wire connections via air). Works just fine and reliably. So if you solder together the blue pill, you can add to any/all pins around its sides such wire and use it for you purposes reliably.

Even if I need to fix the board later, I can just solder end of such wire to the point of existing soldered pin and it is good connection even against ocassional pull-force.

So basically you can attach such wire at the construction time through the hole (one with one pin) or maybe like 4-5 later to the same soldering point (or combine the methods).

Ofcourse connecting far away pins with the wire / capacitor would lead to some capacity to any and all paths it cross over the PCB, but it probably matter ony for noise in analog and for computing the result capacity - which would be more like experimented-out, than exactly computed anyway)

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