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Phil23
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Joined: 27/03/2016
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Posted: 12:36pm 13 Jul 2016

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From a previous thread....

Grogster said
The analogue ground circuit(10R + 100N to GND) that Geoff uses in his MM+ and Maximite series of units are certainly the way to go if you expect to be making any serious analogue measurements. Otherwise, I just directly connect AGND to the surrounding ground-plane...

It does very much depend on what you plan to do.

In other words, if you plan to use analogue measurements in your project, then use the 10R+100N...

Just looking at the MM+ E64 Shematic & I don't see this.

It shows AVdd(Pin 19) with 10R+100nF, but AVdd(Pin 20) to the Common Ground.

So I should modify my circuit as follows:-

AVss->10R<-Ground Plane;
AVss->100nF<-Ground Plane.

Is that correct for the Analogue Ground circuit?
I've already done Analogue Power as recommended,
but still not 100% clear on Analogue Ground.

Thanks

Phil.

Grogster

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Posted: 09:56pm 13 Jul 2016

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On the 1C boards, the resistor is there - R3 and C8.

All R3/C8 do, is just decouple AVdd to remove any little noises that might otherwise be on the analogue supply line if it was DIRECTLY connected to the rest of the Vdd pins.

Just extra filtering for the analog supply pin.

I'm not quite sure what you mean with your ASCII schematic thing above, but Geoff's schematic is correct where the 10R and 100n are concerned.

Pin19 is AVdd(Analog supply voltage), and Pin20 is AVss(Analog supply ground).
Pin19 is connected to 3v3 via the filter, and pin20 is connected to circuit ground with all the other grounds.

Smoke makes things work. When the smoke gets out, it stops!

Phil23
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Posted: 10:04pm 13 Jul 2016

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Grogster said I'm not quite sure what you mean with your ASCII schematic thing above, but Geoff's schematic is correct where the 10R and 100n are concerned.

Pin19 is AVdd(Analog supply voltage), and Pin20 is AVss(Analog supply ground).
Pin19 is connected to 3v3 via the filter, and pin20 is connected to circuit ground with all the other grounds.

What I was trying to explain with the ASCII is do I do something like AVss to the ground plane via a 10 Ohm resistor with a cap across it.

That didn't quite seem logical to me.
0.1�F in parallel with 10 ohms between the 2 grounds doesn't seem to make sense or seemingly do much, but I see references to "decoupling" AVss & in another thread matherp advised me not to just take AVss directly to the ground plane.

Already have AVdd connected as per Geoff's schematics.

Thanks

Phil.

matherp
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Joined: 11/12/2012
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Posted: 10:11pm 13 Jul 2016

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Quote in another thread matherp advised me not to just take AVss directly to the ground plane.

What I was saying is to just have a single point (wire if you like) connection between AVSS and the digital ground. You are trying to avoid large current flows in the ground plane affecting AVSS. The way I do this when laying out a board is to have AVSS as a separate network from VSS and connect the two with a shorting link. Then when the layout is complete I just replace the shorting link with a single track. That way I know that AVSS can only have a single point connection.

Grogster

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Posted: 10:12pm 13 Jul 2016

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Hi.

Quote What I was trying to explain with the ASCII is do I do something like AVss to the ground plane via a 10 Ohm resistor with a cap across it.

NO.

Quote but I see references to "decoupling" AVss & in another thread matherp advised me not to just take AVss directly to the ground plane.

YES.

It's possible that was a typo and whoever wrote that meant to say Vdd. Hell, it could even have been me! I myself mix up Vss and Vdd all the time. Now I prefer to just use GND for ground, and the voltage itself for the voltage pins - like 3v3 or 5v0 etc.

Smoke makes things work. When the smoke gets out, it stops!

Phil23
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Posted: 10:42pm 13 Jul 2016

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matherp said

Quote in another thread matherp advised me not to just take AVss directly to the ground plane.

Ok,

I think I get it.

Building this on prototyping board.

The type that has 3 pin strips running vertically & ground & power strips running horizontally. Power from one side ground from the other.

This stuff.

At the moment all my thermistor's grounds are to a common track, which goes all over the board.

Do I take a close connection to this track directly back to the analogue ground?

Sorry if I seem a bit vague on understanding this end of the connections.

Right now AVss is going to a track about 6 strips away.

Thanks

Phil.Edited by Phil23 2016-07-15

Phil23
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Posted: 11:57pm 15 Jul 2016

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On the Back Packs (Geoff's), is it worth cutting the track to Pin 28 & putting a 10 Ohm resistor on the board to de-couple the AVdd?

MicroBlocks

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Posted: 12:42am 16 Jul 2016

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Make sure there is only one single point that connects digital and analog ground.

Microblocks. Build with logic.

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