Understanding PrISM

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noacc_4030701
Level 1
Level 1

Hi,

I would like to use the PrISM component to change the brightness of a led Matrix.

I have configured the PrISM component with a resolution of 8 bits, the pulse density type as Less Than or Equal.

To change the dimming value, I modify the pulse density with the API function PWM_L_WritePulse0(item), sending and integer from 0 to 255. The dimming is working but is not linear.

I have the following curve:

pastedImage_0.png

How can I make the dimming linear?

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6 Replies
odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted

hello,

I suspect that non-linearity comes from rise-time characteristics of the LED. To test, try reducing PrISM clock frequency; also try PWM instead of PrISM. The issue with PrISM is very high bandwidth, some devices with input threshold may not respond to short pulses correctly due to not fully opening. While using PrISM seems attractive, it's time profile shows occasional long peaks/valleys, changing unpredictably from one PrISM code to another. The LED responds mostly to long peaks/valleys, which becomes non-linear.

/odissey1

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Ekta_N
Moderator
Moderator
Moderator
750 replies posted First like given 250 solutions authored

Hello,

Can you tell which PSoC device ae you using? For PSoC 1 the following application note is available for LED Dimming:

https://www.cypress.com/file/133251/download

Regards

Ekta

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Hi,

I'm using a PSoC 4200L CY8C4246AZI-L433

Regards

Norman

Le lun. 18 mars 2019 à 10:14, EktaN_26 <community-manager@cypress.com> a

écrit :

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Understanding PrISM

reply from EktaN_26

<https://community.cypress.com/people/EktaN_26?et=watches.email.thread>

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Ekta_N
Moderator
Moderator
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750 replies posted First like given 250 solutions authored

Hello.

Did you try reducing the PrISM clock frequency to achieve linear dimming?

Regards

Ekta

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Hi,

Yes I have reduce the clock frequency, and i the dimming is more linear, I

have also tried the PWM component and the output is perfectly linear.

Still i don't get why PrISM does not work, it is suppose be used for this

kind of application:

The PrISM component provides modulationtechnology that significantly

reduces low-frequency flicker and radiated electromagnetic interference

(EMI),which are common problems with high- brightness LED designs.

Regards

Norman

Le mar. 26 mars 2019 à 01:14, EktaN_26 <community-manager@cypress.com> a

écrit :

<http://www.cypress.com>

Cypress Developer Community

<https://community.cypress.com/?et=watches.email.thread>

Understanding PrISM

reply from EktaN_26

<https://community.cypress.com/people/EktaN_26?et=watches.email.thread>

in PSoC Software - View the full discussion

<https://community.cypress.com/message/190802?et=watches.email.thread#190802>

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Ekta_N
Moderator
Moderator
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750 replies posted First like given 250 solutions authored

Hello Norman,

I just wanted to know that, how are you measuring whether the dimming is linear or not?

Regards,

Ekta

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