FEZ Spider + flickering CP7 display

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1

Hi I have a FEZ Spider together with a CP7 display.
Software works fine, only the display is flickering a lot.

Should the CP7 be configured in a special way?
Any suggestions where to look?

TIA Jos

2

may be a power issue. have you tried using a powered USB hub?

3

@ JdV - As mike said, this may be a power issue, however, you may need to use the power extender module. This was made with power hungry modules like large displays in mind:

https://www.ghielectronics.com/catalog/product/441

4

FEZ Spider is powered 5V 1A, 3V3, 800 mA.
CP7 is fed from FEZ Spider.
This should be sufficient isnt’it?

5

No, not necessarily. It’s a display, it’ll suck a lot.

Can you elaborate on how you have the two power supplies running? Are these on a custom regulator setup? What’s the original power source?

6

Original power source: 12 V 2A

Fed 12V into a TracoPower TSR 1-2450 module (switching regulator, 5V 1A output)
The 5V output of the TracoPower module in turn is fed into a LM1117T 3.3 (3.3V 800 mA)

12V IN -> TracoPower TSR 1-2450 -> LM1117T 3.3
| |
|/ |/
5V to FEZ 3.3V to FEZ

7

so you’ll max out the 5v 1a supply before you can draw 800ma. Don’t suppose you have a 2a option? Alternatively, a second 5v 1a that you can use just for the 5v rail? How about current measurement, do you have a multimeter that can give you an idea how much the setup is drawing?

Just off the raw CP7 documented draw, it’s 50ma@ 3v3 and 700ma at 5v. I can’t imagine the Spider alone taking a couple of hundred ma’s at 3v3 but I think this is the likely reason for the flickering, and if you can get yourself some extra capacity you’ll resolve this.

8

Did some measurements. Total current drawn at 12 V is 400 mA (max). Assuming 100% efficiency this yields to 5V, 960 mA (max).

FEZ Spider spec says 160 mA (active state),
CP7 like you said: 5V 700 mA, 3.3 V 50 mA

Adding them all together results in a power consumption of 910 mA so I think there should be enough power available for both FEZ Spider and CP7 display.

So again, what would cause the display to flicker?

9

Could you try to run the below program on the board and see if it flickers? Only connect the four CP7 sockets to the Spider in the designer, no other modules.

namespace GadgeteerApp1
{
    public partial class Program
    {
        void ProgramStarted()
        {
            display_CP7.SimpleGraphics.DisplayRectangle(Gadgeteer.Color.Blue, 0, Gadgeteer.Color.Blue, 0, 0, display_CP7.Width / 2, display_CP7.Height / 2);
            display_CP7.SimpleGraphics.DisplayRectangle(Gadgeteer.Color.Green, 0, Gadgeteer.Color.Green, 0, display_CP7.Height / 2, display_CP7.Width / 2, display_CP7.Height / 2);
            display_CP7.SimpleGraphics.DisplayRectangle(Gadgeteer.Color.Yellow, 0, Gadgeteer.Color.Yellow, display_CP7.Width / 2, 0, display_CP7.Width / 2, display_CP7.Height / 2);
            display_CP7.SimpleGraphics.DisplayRectangle(Gadgeteer.Color.Purple, 0, Gadgeteer.Color.Purple, display_CP7.Width / 2, display_CP7.Height / 2, display_CP7.Width / 2, display_CP7.Height / 2);
            display_CP7.ScreenPressed += (a, b) => display_CP7.SimpleGraphics.DisplayEllipse(Gadgeteer.Color.Red, (uint)b.touchPos[0].xPos, (uint)b.touchPos[0].yPos, 5, 5);
        }
    }
}
10

910 == still too close for me !!! Its within 10%. I still would look for more headroom.

I agree that the more likely scenario there is under 900ma thru the 5v reg, with likely efficiencies - but you know power supplies, you put them close to their limits and you can increase noise on the power lines (and what might noise look like? flickering… )

11

Took my lab power supply this morning to get things more clear.
Loaded John’s program on FEZ Spider.

The display doesn’t flicker as long as I keep the voltage high enough and allow the 5V regulator to do its job.

Next connected the display to the power supply that made the display flicker and the flickering was back.Turns out the 5V regulator was too noisy, causing the display to flicker.

Thanks for supporting me guys.

Jos

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