Surf PI 1.2 - Big Jitter on pin 1 of LM358. How to get rid of it?

[Polymer]

Surf PI 1.2 - Big Jitter on pin 1 of LM358. How to get rid of it?

It's the signal taken from PIN 1 of the LM358 after the 22k resistor (before the diode).

Here's what it looks like:

That yellow line jumps up and down like crazy.
This messes with my threshhold.

It does not occur when coil is disconnected.

What can be done about this?

[homefire]

Are you powering it from a Bench Supply ? If so use a Battery.

Is it showing up at the out put of 7660 ? Pin 8 ?

[Polymer]

Are you powering it from a Bench Supply ? If so use a Battery.

Is it showing up at the out put of 7660 ? Pin 8 ?

Thanks for your input homefire.

I have a Bench Supply with transformer - much more quiet than the switched ones.
That wasn't the problem. The same signal jitter occurs when powered by batteries too.

The jitter does not show up on pin 8 of the 7660. I have a nice flatline there.

I've changed all chips, disconnected the osc pin of the 7660
and unplugged everything in the room, including the usb-dso and netbook powered down.

Dang, I can still hear this erratic sound from the Surf PI.

I will be taking the pcb and oscilloscope to a remote place tomorrow.

Maybe it's something in the area here, although it's 3:30am right now. Arghhhhhhh.

Any other ideas? Hopefully ...

Oh, yes - I am wondering why the jitter is only on the top part of the yellow signal.

[homefire]

Using Florescent Lighting ? Noise is on the Positive Rail from something. C7 Leaking creating the noise ?

[Qiaozhi]

Surf PI 1.2 - Big Jitter on pin 1 of LM358. How to get rid of it?

It's the signal taken from PIN 1 of the LM358 after the 22k resistor (before the diode).

Here's what it looks like: [ATTACH]40454[/ATTACH]

That yellow line jumps up and down like crazy.
This messes with my threshhold.

It does not occur when coil is disconnected.

What can be done about this?

What does the signal look like on pin 7 of the LM358?
I assume the voltages on pins 8 and 4 are stable?

[Polymer]

Using Florescent Lighting ? Noise is on the Positive Rail from something. C7 Leaking creating the noise ?

I don't have any florescent lighting nor CFL's. I hate them.

I went dark aka I threw the main fuse of the house out of frustration.
That annoying sound was still coming out of the speaker.

I will get around to checking C7 once I've replied to Qiaozhi's questions.

Measuring what he asked might be a clue that points towards the 7660S, although I've already swapped em again.

[Carl-NC]

Since it goes away when disconnecting the coil, try rotating the coil toward different directions. If it's external interference you will see it vary and probably can find a decent null point.

[Polymer]

What does the signal look like on pin 7 of the LM358?
I assume the voltages on pins 8 and 4 are stable?

Thanks for your reply Qiaozhi.

The negative rail appears unstable - Pin 4 of LM358
The positive rail appears to be ok. - Pin 8 of LM358
Two screen shots in DC & AC mode:




Output pin 7 of lm358:



Perhaps you can make something of the screenshots.

Sorry for the short text, but I'm going for a run now ... before I start doing silly things to the PCB ... I'm frustrated

[Qiaozhi]

Thanks for your reply Qiaozhi.

The negative rail appears unstable - Pin 4 of LM358
The positive rail appears to be ok. - Pin 8 of LM358
Two screen shots in DC & AC mode:

[ATTACH]40456[/ATTACH]
[ATTACH]40457[/ATTACH]

Output pin 7 of lm358:

[ATTACH]40458[/ATTACH]

Perhaps you can make something of the screenshots.

Sorry for the short text, but I'm going for a run now ... before I start doing silly things to the PCB ... I'm frustrated

OK - there's some switching noise on the negative power rail from the 7660 that's not synchronized with the TX oscillator, but it doesn't seem bad enough to be causing the problem. It looks to me like the noise is external to the circuit. I would try Carl's suggestion of repositioning the coil to see if you can identify the direction of the interference. You might also want to check that the screen to the coil is connected to GND (0V).

[DOOLEY]

POLYMER, do you have any battery powered analog clocks in the house ??
i experienced similar problems a few years back,
took battery out of clock !!

instantly allot better,
1 second pulse from the analog clocks coil !!

i live in a semi-detatched, could still detect neighbors kitchen clock, dang !!

deff worth syncing the 7660...........

just my 2 peneths worth

[Polymer]

Hello DOOLEY, Qiaozhi, Carl-NC,

Thank you for all your hints!

I have been testing like a crazy monkey and seem to have come across what might be going on.
It looks like a composite problem - internal to PCB and external EMI.

I sometimes got the jitter when testing and then it was gone.

I have an external pot to adjust frequency slightly to counter EMI beat frequency.
I looked at the jitter, adjusted the pot and the jitter came and went.
This was WITHOUT the coil being connected I then realized.

Somehow the 7660S is not always synching and causing immense to no beat frequencies dependent on frequency of 555.

Before I follow through on all your EMI related hints, I'd like to implement a split power supply without the 7660S.
That's so I can see what is 7660S related and what is external EMI. Maybe it will help me sort out the problem.

Would the following work as a split PSU? Can I connect them like in the picture?
I still don't do well with pos/neg power rails and reference points, it jumbles my mind.
What to do with the 0v of the battery pack - is it equivalent to ground on PCB?



Cheers and with appreciation, Polymer

[Qiaozhi]

Hello DOOLEY, Qiaozhi, Carl-NC,

Thank you for all your hints!

I have been testing like a crazy monkey and seem to have come across what might be going on.
It looks like a composite problem - internal to PCB and external EMI.

I sometimes got the jitter when testing and then it was gone.

I have an external pot to adjust frequency slightly to counter EMI beat frequency.
I looked at the jitter, adjusted the pot and the jitter came and went.
This was WITHOUT the coil being connected I then realized.

Somehow the 7660S is not always synching and causing immense to no beat frequencies dependent on frequency of 555.

Before I follow through on all your EMI related hints, I'd like to implement a split power supply without the 7660S.
That's so I can see what is 7660S related and what is external EMI. Maybe it will help me sort out the problem.

Would the following work as a split PSU? Can I connect them like in the picture?
I still don't do well with pos/neg power rails and reference points, it jumbles my mind.
What to do with the 0v of the battery pack - is it equivalent to ground on PCB?

[ATTACH]40472[/ATTACH]

Cheers and with appreciation, Polymer

I would suggest having look at how the TX in the Minipulse Plus is synchronized to the voltage converter. The same idea should also work with the 7660.

[Polymer]

I would suggest having look at how the TX in the Minipulse Plus is synchronized to the voltage converter. The same idea should also work with the 7660.

Hmmm. Is it this what you mean:



What is the equivalent to the -VB on the Minipulse Plus in relationship to the voltage designations on the Surf PI?

[Qiaozhi]

Hmmm. Is it this what you mean:

[ATTACH]40476[/ATTACH]

What is the equivalent to the -VB on the Minipulse Plus in relationship to the voltage designations on the Surf PI?

I've just noticed that ionut_mtb has posted an image of the original White's Surf-PI schematic, which does include synchronization of the 7660 with the TX OSC. Simply add D7 ( 1N4148 ) and R27 ( 10k ).

[Polymer]

I've just noticed that ionut_mtb has posted an image of the original White's Surf-PI schematic, which does include synchronization of the 7660 with the TX OSC. Simply add D7 ( 1N4148 ) and R27 ( 10k ).

Quick feedback - this helped a great deal! YAY

Now to go about solving possible EMI issues ...