Odd behaviour with 4.3inch screen

DjDemonD · 1 Apr 2018, 21:24

So I'm using a duet3d paneldue board but with a chinese 4.3inch screen https://www.aliexpress.com/item/4-3-5-7-Touch-Screen-Fitting-PanelDue-Colour-Controller-For-3D-Printers-CNC-Machines-DuetWifi/32847883880.html?spm=a2g0s.9042311.0.0.I2DfRG

When its connected it works, but I'm getting strange interference which is making my temperatures fluctuate like this:

I unplugged the paneldue at the point where temps go back to stable.

Any ideas?

dc42 · 2 Apr 2018, 08:48

What temperature sensors are they; and where is the 5V power to the PanelDue coming from?

DjDemonD · 2 Apr 2018, 09:45

They are PT1000s and the duetwifi and panel due is being powered from external usb (2A).

DjDemonD · 4 Feb 2018, 09:48

I think I have it figured out the screen was temporarily lying against the side of the psu probably creating some sort of ground loop.

DjDemonD · 2 Apr 2018, 09:50

No I thought it was that but it isn't its still doing it.

DjDemonD · 2 Apr 2018, 09:51

It's definitely the screen not the paneldue board if I disconnect the screen it doesn't happen.

dc42 · 2 Apr 2018, 10:03

It's probably the screen generating ripply on the 5V supply, which is somehow getting fed through to the ADC. With PT1000 sensors, a single ADC count change corresponds to a significant temperature change. Do you get the same problem if you power them using the Duet's own 5V regulator, or if you power them from independent USB supplies?

I guess it's also possible that the screen is inducing noise on the PT1000 wires and the filtering in the Duet isn't quite good enough to filter all of it out.

Does the problem only occur when the screen is running at less than full brightness?

DjDemonD · 2 Apr 2018, 12:40

So screen brightness doesn't affect this behaviour.

If I remove the 5v EXT jumper with PSU ON the behaviour remains the same. If I attach the jumper to the INT 5V header, then it stops being erratic.

Could I power the paneldue from the 5v INT header? this would I think leave the 5V EXT jumper in place so the duetwifi remained powered by the USB 5v, but solve the ripple problem?

DjDemonD · 3 Apr 2018, 20:10

An update to this, if I run the genuine Paneldue/Chinese screen combo from external usb power via the Paneldue usb port it works fine no interference or erratic temperature readings. I tried running it from the INT 5v jumper but this did not work.