"Noisy" tpsDOT

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robs
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Re: "Noisy" tpsDOT

Post by robs »

JasonC SBB wrote: You need to connect the scope probe ground clip to the TPS signal ground, and nowhere else. Other channel probes should not be grounded elsewhere.

The signal at the A/D input will be the same, plus noise picked up by the cabling, plus noise that gets through bad PCB layout and grounding. This assumes that there is only one path for the current to flow from the TPS signal ground, to the A/D analog ground pin. (If not there will be ground offsets which can manifest as a DC offset, high frequency noise, or a combo).
If that's right I really don't understand anything about electronics. Just to make sure we're talking about the same thing, in the schematic:
schem.png
Would my probing at TPS really have given the same result as probing at AD3-1 (which connects to the CPU's AD pin)?

On the other point, is it completely illegitimate to separately probe signal and ground with the probe grounds to a common point and subtract the signals, or is it just not best practice? I thought it'd be interesting to see how much noise was on the ground pin, and how much on the signal. I also thought that pulling the signal ground to the scope's ground might hide some of the noise which I wanted to see. I am shaky on this stuff and would certainly like to understand it better.

Have fun,

Rob.
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Re: "Noisy" tpsDOT

Post by robs »

Peter Florance wrote: The test would be to unplug the MS; at that point the gnd terminals of sensors (TPS CLT MAT) should not have continuity to the vehicle ground.
Thanks Peter. Certainly an easy test and I'll definitely do it next time I have access to the MS. Kinda wish I hadn't gone to the bother of mounting it behind the dash.

Have fun,

Rob.
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Re: "Noisy" tpsDOT

Post by Peter Florance »

robs wrote:
JasonC SBB wrote: You need to connect the scope probe ground clip to the TPS signal ground, and nowhere else. Other channel probes should not be grounded elsewhere.

The signal at the A/D input will be the same, plus noise picked up by the cabling, plus noise that gets through bad PCB layout and grounding. This assumes that there is only one path for the current to flow from the TPS signal ground, to the A/D analog ground pin. (If not there will be ground offsets which can manifest as a DC offset, high frequency noise, or a combo).
If that's right I really don't understand anything about electronics. Just to make sure we're talking about the same thing, in the schematic:
schem.png
Would my probing at TPS really have given the same result as probing at AD3-1 (which connects to the CPU's AD pin)?

On the other point, is it completely illegitimate to separately probe signal and ground with the probe grounds to a common point and subtract the signals, or is it just not best practice? I thought it'd be interesting to see how much noise was on the ground pin, and how much on the signal. I also thought that pulling the signal ground to the scope's ground might hide some of the noise which I wanted to see. I am shaky on this stuff and would certainly like to understand it better.

Have fun,

Rob.
Rob, if the sensor ground is not connected to the car anywhere, it should not be sinking appreciable amounts of current and it's voltage should be the same from the MS ground plane to anywhere on the sensor commons. If the sensor ground is grounded to the car, then it can try to sink some MS current and some noise can be introduced.

What some are ignoring is the polyfuse noise can be duplicated on the stim.
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Re: "Noisy" tpsDOT

Post by weeblebiker »

just finished reading this all the way through. glad to read the tps/map dot noise issues I've been fighting with is being addressed(along with addressing the pid's).

Now something to consider from the peanut gallery on signal noise reduction.

Doing hardware mods and electrical mods on existing installs to improve performance should be expected by everyone running ms (or anyone into moding to cars for that matter). We all know ms a diy share ware concept, and most of us know every single install has it's own individual issues.

Remember many of us got into ms for the challenge and learning involved in integrating fluid dynamics, EE and programing into a well running system. If we were just looking for easy, we'd sell the car we got and buy something with more horse power.

Expecting us to be simply looking for a firmware update to take care of our individual issues is possibly a little bit egocentric on the programmers part: we are not your workplace consumers and we didn't pay out the nose for a plug and play system installed by "professionals", we got ms and not a big name stand alone system for a reason.

That said

It'd be nice to get to a summerization and short rational (in laymens terms) of the hardware/electrical fixes and filters with the corisponding wiring diagrams from the EE's in addition to the code changes the programers have hammered out (which get summerized in firmware releases)

cheers everyone for some great info and applicable improvements :yeah!:
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Re: "Noisy" tpsDOT

Post by JasonC SBB »

robs,

Excuse my hiatus, I was doing some experimentation (which I will post about elsewhere on the MS boards)

Peter is correct.

Consider these 3 wires:
1) From TPS output in engine bay to MS TPS input pin
2) From TPS ground in engine bay to MS Sensor Ground pin which is connected via the PCB layout to the A/D input gnd
3) From engine block/head to MS high current ground pin

If wires #1 and #2 have no appreciable current through them, then there will be no voltage drop across them. Therefore the voltage at the MS from the TPS input pin to the sensor ground pin will be the same as the voltage at the TPS.
If the PCB layout is tight, then the voltage from AD3-1 to the A/D grnd pin will be the same voltage but filtered by the CRC pi filter.

Wire #3 carries large currents. These currents produce a DC voltage drop V = I*R.
Additionally said currents have di/dt. Wire #3 will have some inductance. This produces an additional voltage drop V = L * di/dt. This voltage tends to look spikey. If the di/dt lasts for say, 10 us, then the spike is about 10 us wide. This is the kind of noise easily filtered out by an RC filter. The sum of these 2 voltages is the noise voltage on wire #3. Therefore if you measure the voltage at the MS pins, from the TPS input, to the high current ground pin, it will be equal to TPS voltage plus said noise voltage.

The assumption that there is no appreciable current going through wire #2 will NOT be valid if, due to the layout, there is a conductor, such as a PCB trace (or a polyfuse!), through which the currents for wire #2 and wire #3 both flow! It gets worse as the resistance or impedance of the shared conductor is increased. This is called "shared impedance" or "shared conductor" noise coupling. It has the very bad misnomer, "ground loop". This is what I suspect is happening with the polyfuse. (i.e. shorting it out reduces the noise)

On the MS PCB layout the sensor gnd and the high current ground pins are connected together via the polyfuse. The polyfuse separates the grounds of two groups of circuits.

The problem is that the polyfuse has resistance and any currents flowing through it will produce a voltage drop. This voltage drop appears as a voltage between the grounds of the 2 systems. (This is in addition to the shared impedance noise coupling above) The current through the polyfuse is the sum total of ground return currents of any currents of the signals that go from one system to the other. In addition to the IR drop, there is an additional drop due to the increased inductance from enlarging the loop area of the di/dt of said currents, producing spikey voltage drops due to the inductance. This is what caused the noise in the AEM that I fixed in this post:
http://www.msextra.com/forums/viewtopic ... tt#p315544


Clear as mud?
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Re: "Noisy" tpsDOT

Post by racingmini_mtl »

JasonC SBB wrote:The assumption that there is no appreciable current going through wire #2 will NOT be valid if, due to the layout, there is a conductor, such as a PCB trace (or a polyfuse!), through which the currents for wire #2 and wire #3 both flow! It gets worse as the resistance or impedance of the shared conductor is increased. This is called "shared impedance" or "shared conductor" noise coupling. It has the very bad misnomer, "ground loop". This is what I suspect is happening with the polyfuse. (i.e. shorting it out reduces the noise)

On the MS PCB layout the sensor gnd and the high current ground pins are connected together via the polyfuse. The polyfuse separates the grounds of two groups of circuits.

The problem is that the polyfuse has resistance and any currents flowing through it will produce a voltage drop. This voltage drop appears as a voltage between the grounds of the 2 systems. (This is in addition to the shared impedance noise coupling above) The current through the polyfuse is the sum total of ground return currents of any currents of the signals that go from one system to the other. In addition to the IR drop, there is an additional drop due to the increased inductance from enlarging the loop area of the di/dt of said currents, producing spikey voltage drops due to the inductance. This is what caused the noise in the AEM that I fixed in this post:
http://www.msextra.com/forums/viewtopic ... tt#p315544


Clear as mud?
Jason,

That's not how the polyfuse is connected on the MS board. Look at these 2 schematics which show both polyfuses (F1 and F2): http://www.msextra.com/doc/general/ms2v3schems.html#p6 and http://www.msextra.com/doc/general/ms2v3schems.html#p8. Both of them are only on the 5V supply and have nothing to do with ground or high current.

Jean
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Re: "Noisy" tpsDOT

Post by robs »

JasonC SBB wrote: Excuse my hiatus, I was doing some experimentation (which I will post about elsewhere on the MS boards)
Nothing to excuse. Haven't been active here myself -- a holiday for everyone.
JasonC SBB wrote: Peter is correct.

Consider these 3 wires:
1) From TPS output in engine bay to MS TPS input pin
2) From TPS ground in engine bay to MS Sensor Ground pin which is connected via the PCB layout to the A/D input gnd
3) From engine block/head to MS high current ground pin

If wires #1 and #2 have no appreciable current through them, then there will be no voltage drop across them. Therefore the voltage at the MS from the TPS input pin to the sensor ground pin will be the same as the voltage at the TPS.
If the PCB layout is tight, then the voltage from AD3-1 to the A/D grnd pin will be the same voltage but filtered by the CRC pi filter.
OK, some subtlety in the language there which is probably understood by the experts, but I had to read it through a couple of times. By "no voltage drop across them", you mean from end to end of each wire, not between #1 and #2, right? Must be, since that's the whole point of the TPS. So yes, I expect the voltages at the MS connector to be much the same as at the other end of the wire at the TPS. Those weren't the voltages I wanted. I wanted a capture so I could simulate what the AD pin would read, which meant on the CPU side of the filter and I think you have confirmed above that the voltages there will be different (i.e. filtered). That being the whole point of the filter.

Just as an aside, referring to the filter as a "CRC pi filter" sent me off to Google to see what interesting relationship it had to pi -- complex arithmetic of capacitor charge, Euler's formula and such like. Ha. It's because the schematic looks like the letter pi. You guys!
JasonC SBB wrote: Wire #3 carries large currents. These currents produce a DC voltage drop V = I*R.
Additionally said currents have di/dt. Wire #3 will have some inductance. This produces an additional voltage drop V = L * di/dt. This voltage tends to look spikey. If the di/dt lasts for say, 10 us, then the spike is about 10 us wide. This is the kind of noise easily filtered out by an RC filter. The sum of these 2 voltages is the noise voltage on wire #3. Therefore if you measure the voltage at the MS pins, from the TPS input, to the high current ground pin, it will be equal to TPS voltage plus said noise voltage.
Is this right for what I want to do? Seems to me that what I'd need to do to see what the CPU is actually seeing at the AD pin is to capture the waveform at that pin, with the probe grounded at the ADC ground pin -- if noise is introduced to the signal ground by the high current grounds (or whatever) that will be seen here. But further, is there nothing in my reasoning: as I understand it, the scope's ground (the probe ground too) is itself grounded to the earth pin at the wall socket -- and I don't believe this is through any great resistance. Couldn't this affect the spikes on the ADC ground pin's voltage and end up giving me a more stable signal than the CPU sees when the probe ground isn't there? That at least was my rationale for probing both ground and signal (albeit in the wrong, but easily accessible place) with the battery -ve as the ground.
JasonC SBB wrote: Clear as mud?
I am interested in the polyfuse question and understand how even a very small resistance in the wrong place can spoil your day. I'll continue to read along with interest, but others have much more to offer. I appreciate your explanations.

Have fun,

Rob.
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Re: "Noisy" tpsDOT

Post by piledriver »

Not to go all "Matrix" on you, but There Is No Ground, all is relative, even within single circuits.

"ground" is a trick we play on ourselves --- a construct, a convention--- to help get our head around all things electric.
It usually works as you would think, except when it doesn't.

The probe in the circuit even throws a variable in the works, although a very small one by design.

use the a2d ground as a reference... really, that's as close to what the a2d "sees" as you are going to get other than its digital output.

This way madness lies, test what you proposed (hook the probe ground to the wall socket gnd or scope case gnd and the probe to the a2d input) and let us know how it goes.
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Re: "Noisy" tpsDOT

Post by JasonC SBB »

racingmini_mtl wrote: Jason,

That's not how the polyfuse is connected on the MS board. Look at these 2 schematics which show both polyfuses (F1 and F2): http://www.msextra.com/doc/general/ms2v3schems.html#p6 and http://www.msextra.com/doc/general/ms2v3schems.html#p8. Both of them are only on the 5V supply and have nothing to do with ground or high current.

Jean
Forgive me as there was an earlier discussion elsewhere that discussed a polyfuse that connected 2 ground systems.

In any case if a polyfuse in a 5V line is used, there must be a decoupling capacitor connected after it. If not this is one place noise can get in. The polyfuse increases the 5V source impedance and pulsating loads on it will cause pulsations in the 5V reference. Does the MS have one?
Last edited by JasonC SBB on Wed Apr 11, 2012 12:38 pm, edited 1 time in total.
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Re: "Noisy" tpsDOT

Post by JasonC SBB »

piledriver wrote:Not to go all "Matrix" on you, but There Is No Ground, all is relative, even within single circuits.

"ground" is a trick we play on ourselves --- a construct, a convention--- to help get our head around all things electric.
It usually works as you would think, except when it doesn't.
This is a great Jedi truism.

A ground isn't a ground isn't a ground....

Which is why in mixed signal systems, I am loathe to use the ground symbol at all.
The probe in the circuit even throws a variable in the works, although a very small one by design.

use the a2d ground as a reference... really, that's as close to what the a2d "sees" as you are going to get other than its digital output.
What newbies have to wrap their head around is, the A/D "sees" the voltage right at the input on the die. In my day job, even 2mm long bond wires inside a chip have voltage drops that need to be considered!
Last edited by JasonC SBB on Wed Apr 11, 2012 12:50 pm, edited 1 time in total.
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Re: "Noisy" tpsDOT

Post by JasonC SBB »

robs wrote:
JasonC SBB wrote: Peter is correct.

Consider these 3 wires:
1) From TPS output in engine bay to MS TPS input pin
2) From TPS ground in engine bay to MS Sensor Ground pin which is connected via the PCB layout to the A/D input gnd
3) From engine block/head to MS high current ground pin

If wires #1 and #2 have no appreciable current through them, then there will be no voltage drop across them. Therefore the voltage at the MS from the TPS input pin to the sensor ground pin will be the same as the voltage at the TPS.
If the PCB layout is tight, then the voltage from AD3-1 to the A/D grnd pin will be the same voltage but filtered by the CRC pi filter.
OK, some subtlety in the language there which is probably understood by the experts, but I had to read it through a couple of times. By "no voltage drop across them", you mean from end to end of each wire, not between #1 and #2, right?
Correct.
Just as an aside, referring to the filter as a "CRC pi filter" sent me off to Google to see what interesting relationship it had to pi -- complex arithmetic of capacitor charge, Euler's formula and such like. Ha. It's because the schematic looks like the letter pi. You guys!
Sorry sometimes it's hard for me to know what my audience knows or doesn't know. I sometimes have the opposite problem talking to newbie engineers, I over-explain something they already know. BTW there is also such a thing as a "T" filter. :) Maybe it's got something to do with the fact that analog engineers are a rare breed and the old timers who blazed trails were all strange animals.

JasonC SBB wrote: Wire #3 carries large currents. These currents produce a DC voltage drop V = I*R.
Additionally said currents have di/dt. Wire #3 will have some inductance. This produces an additional voltage drop V = L * di/dt. This voltage tends to look spikey. If the di/dt lasts for say, 10 us, then the spike is about 10 us wide. This is the kind of noise easily filtered out by an RC filter. The sum of these 2 voltages is the noise voltage on wire #3. Therefore if you measure the voltage at the MS pins, from the TPS input, to the high current ground pin, it will be equal to TPS voltage plus said noise voltage.
Is this right for what I want to do? Seems to me that what I'd need to do to see what the CPU is actually seeing at the AD pin is to capture the waveform at that pin, with the probe grounded at the ADC ground pin -- if noise is introduced to the signal ground by the high current grounds (or whatever) that will be seen here. [/quote]This is strictly correct. In the real world, what I would do is, if the AD output has spikey noise on it, is look for grounding and layout mistakes, and maybe probe the pins as you describe as a verification step.

But further, is there nothing in my reasoning: as I understand it, the scope's ground (the probe ground too) is itself grounded to the earth pin at the wall socket -- and I don't believe this is through any great resistance.
Depends on your 'scope.
Couldn't this affect the spikes on the ADC ground pin's voltage and end up giving me a more stable signal than the CPU sees when the probe ground isn't there?
It can but most likely not. This is because in effect you will be grounding the car to the house wiring. If there are no currents flowing through this new connection then there will be no noise introduced in the measurement. If the point on the car that you are grounding via the oscilloscope has a large dv/dt on it, you will introduce "capacitive displacement currents" and the reading will be contaminated.
That at least was my rationale for probing both ground and signal (albeit in the wrong, but easily accessible place) with the battery -ve as the ground.
In practice, given that the dv/dt on the signal ground, and the engine block/chassis are small, neither setup will cause distortion due to the fact that the scope ground clip is effectively connected to the home wiring. For the purpose of reading the TPS signal, you will want to simply ground the scope probe to the TPS ground pin. If you want to have a noise free reading, don't ground another probe to any other point on the car. This is because the grounds on the various scope probes are connected together, and the resulting current you will force up and down the probe shields will induce noise in your reading.
I am interested in the polyfuse question and understand how even a very small resistance in the wrong place can spoil your day. I'll continue to read along with interest, but others have much more to offer. I appreciate your explanations.
Is or isn't there a polyfuse in the ground? ...
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Re: "Noisy" tpsDOT

Post by dontz125 »

JasonC SBB wrote:In any case if a polyfuse in a 5V line is used, there must be a decoupling capacitor connected after it. If not this is one place noise can get in. The polyfuse increases the 5V source impedance and pulsating loads on it will cause pulsations in the 5V reference. Does the MS have one?
Sort of - the V3.0 board has an inductor and cap going to VddSyn (for the MS1 chip), and an inductor and 2 caps and a second polyfuse going to the VRef out-line, but these are after the tap-off for "Vcc" and the 5v points at the proto area, and parallel with the 5.6v Zener. The MicroSquirt and MicroSquirt Module have no caps after the polyfuse, just the Zener covering the 5v plane, then one inductor and the second polyfuse going to the VRef pin.

There is no direct connection I can see between any polyfuse and ground.
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Re: "Noisy" tpsDOT

Post by robs »

JasonC SBB wrote: If the point on the car that you are grounding via the oscilloscope has a large dv/dt on it, you will introduce "capacitive displacement currents" and the reading will be contaminated.
That's what I thought. Since there is a question of noise on the sensor ground I thought it might find somewhere to hide in a couple of hundred feet of earth wire if I hooked the sensor ground to the scope chassis. Hence hooking a second probe to the sensor ground, with both probes grounded to the car chassis (and house's earth). The effective signal is then the difference in the probe voltages.

It was quite a while ago that I learnt (with a modest fireworks display) not to treat the probe and its ground clip as interchangeable, as you might with a voltmeter's probes, and maybe have become neurotic about it. But while you and piledriver emphasise that "ground" is an artificial concept, it does still have to be a fixed voltage doesn't it? You couldn't hook the ground clip to a carrier waveform and read the carried signal at the probe could you? Even if nothing melted, the waveform would be corrupted. Right?

Have fun,

Rob.
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Re: "Noisy" tpsDOT

Post by piledriver »

Note there are several diferent standard ground symbols for a reason...
It's not at all unusual to see a schematic with at least two or three different groundplanes, each with a different symbol.
Sometimes those "groundplanes" might be running at 10KV relative to each other... Transformers are neat devices.
robs wrote: You couldn't hook the ground clip to a carrier waveform and read the carried signal at the probe could you? Even if nothing melted, the waveform would be corrupted. Right?

Have fun,

Rob.
No... well not exactly, but a scope can be floated for example on a HV DC so as to look at tiny AC signal/noise riding on it.
This was common/regularly required in the days of tubes, and I can't think of a scope ever made that will not allow that and other sorts of hairy differential measurements to be made, as that's largely what they exist for.

(safer to use 2 channels and add or subtract assuming the scope supports it, either analog or digitally, but for some work floating the scope is a necessity)

Do Not Lick The Scope When Doing This.
The knobs/case are all insulating plastic for good reason...
Keeping one hand in your pocket when working is not a sign of a slacker in EE, it's a proven survival technique.
Last edited by piledriver on Wed Apr 11, 2012 7:07 pm, edited 1 time in total.
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Re: "Noisy" tpsDOT

Post by Peter Florance »

There is a polyfuse F2 between Vref and the "Vref" pin on the DB37
As current is drawn from from Pin 26 through F2, the 5 volt supply "VRef" on the DB37 can differ from what the processor uses in its ratio-metric (fraction of Vref) measurement. And I'm not sure how "nice" they behave when they do exhibit a voltage drop. Perhaps it not just DC but AC too?

A 5k TPS should only draw 1ma. But hall effect sensors? Maybe a good reason to power them from 12V. I note that on 2001 BMW, it appears that all active sensors are powered from 12v. Only resistance sensors are powered from 5V. Perhaps we should take a clue from them.

External MAP sensor seems like a possible issue; not sure how much current they draw.

Further I have to repeat that as long as sensor ground wire does not carry current, there should not be a issue with noise or voltage offset on it. But if you connect the sensor ground wire to vehicle, you are asking it to help sink current from the MS box and it is no longer a reference, but a conductor.

Makes sense?
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Re: "Noisy" tpsDOT

Post by piledriver »

Makes perfect sense, which is why I completely ignored the Megamanuals install instructions to ground everything at the block and set mine up the way I know to be correct from decades of fixing weird.(or at least as correct as possible)

There's WAY too much current/alternator/ignition noise going through the block as it wishes to plug that anywhere in any sensor circuit, or anything that even potentially connects to a sensor circuit in any possible manner.

On an ACVW with the engine out back and a "remote" battery usually 18" from where you install the MS under the back seat or in the package tray, the sensible way is ground ~everything at the MS mounting plate and run a short fat ground braid to the battery. NOTHING connects to the block except power grounds for the LS2 coils and even then, they and the injectors get their own 12V relay and supply right off the battery. Splitting off and running the sensor and power drive cables on opposite sides of the vehicle doesn't hurt either, avoids inducted noise, critical as everything is common mode ground, not differential.

I don't think a Hall sensor would matter where it gets it's external power, but where you get the 5v or 12v signal pullup might matter, worth discussion. (I pulled it off the input to the 5v reg, but my 1.01 boards are probably small signal basket cases anyway, thus the paranoid install)

Ideally, If your mainboards ground planes were split up properly, and/or if you have all external power drivers for coils/injectors, the MAP/TPS/etc sensors go to their own dedicated signal ground pin(s). Some ferrites might be a good idea...
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Re: "Noisy" tpsDOT

Post by dontz125 »

Peter Florance wrote:A 5k TPS should only draw 1ma. But hall effect sensors? Maybe a good reason to power them from 12V. I note that on 2001 BMW, it appears that all active sensors are powered from 12v. Only resistance sensors are powered from 5V. Perhaps we should take a clue from them.

External MAP sensor seems like a possible issue; not sure how much current they draw.
The MPX4250A draws 8-10mA; the 1GT101DC GTS that James likes draws 20-40mA.
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Re: "Noisy" tpsDOT

Post by 1031 »

Hello to all..
Things go bit too theorical here.. :mrgreen: (sometimes it is good) but some thing´s that i must point out.
When i looked culprit for that noise, i had o-scope ground connected to mega´s sensor "return GND" and there i started to look those voltages (this happen´d at my workplace, mega was connected to stim all the time)
all voltage´s looked clean... i use allways ac-coupling function to check how much there is AC-component "riding top of DC", because it is easy to see by using lower V/div setting. That Vref (+5V out of reg) was near perfect DC (as good as regulator can give) No noise or spikes just pure DC.. so that was before polyfuse..so same connection.. after polyfuse there was that noise.
Speculations here point´s out that was related to common mode noise or scopes´s ground connection etc. If that was case, how that DC before polyfuse was perfect :?:
Another point that has pointed out was adding capacitance after polyfuse, yes i tested that, whit normal electrolyts (good quality Panasonic FM series and also Sanyo´s OS-CON´s that have wery low ESR at wide freq.range) but none of those worked as replacing that polyfuse by normal fuse. So i must say that at this case noise was related only to Vref´s impedance (series resistance of that polyfuse)
JasonC SBB
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Re: "Noisy" tpsDOT

Post by JasonC SBB »

dontz125 wrote:
JasonC SBB wrote:In any case if a polyfuse in a 5V line is used, there must be a decoupling capacitor connected after it. If not this is one place noise can get in. The polyfuse increases the 5V source impedance and pulsating loads on it will cause pulsations in the 5V reference. Does the MS have one?
Sort of - the V3.0 board has an inductor and cap going to VddSyn (for the MS1 chip), and an inductor and 2 caps and a second polyfuse going to the VRef out-line,
0.1 uF is way too small. It needs to be more like a low-ESR 470 uF capacitor.

Would anyone want to try keeping the polyfuse(s) and adding a big capacitor after the inductor(s)?
Peter Florance
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Re: "Noisy" tpsDOT

Post by Peter Florance »

JasonC SBB wrote:
dontz125 wrote:
JasonC SBB wrote:In any case if a polyfuse in a 5V line is used, there must be a decoupling capacitor connected after it. If not this is one place noise can get in. The polyfuse increases the 5V source impedance and pulsating loads on it will cause pulsations in the 5V reference. Does the MS have one?
Sort of - the V3.0 board has an inductor and cap going to VddSyn (for the MS1 chip), and an inductor and 2 caps and a second polyfuse going to the VRef out-line,
0.1 uF is way too small. It needs to be more like a low-ESR 470 uF capacitor.

Would anyone want to try keeping the polyfuse(s) and adding a big capacitor after the inductor(s)?
I wonder if it would be more efficient for you to get your hands on a V3 board instead of working by remote?
Peter Florance
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