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DLP4500: LED current setting

Raymond Tan1
Prodigy 85 points
Part Number: DLP4500
Other Parts Discussed in Thread: DLPC350,

Hello，

I found out that in DLPC350_api.cpp, the function DLPC350_setLedCurrents takes in rgb values that are subtrated from 255. For example this is the code in mainwindow.cpp:       

RedCurrent = 255-strToNum(ui->lineEdit_RedLEDCurrent->text());
GreenCurrent = 255-strToNum(ui->lineEdit_GreenLEDCurrent->text());
BlueCurrent = 255-strToNum(ui->lineEdit_BlueLEDCurrent->text());

1. Can you explain why does it need to subtrate the current value from 255? As to what I understand, 0x00 is the lowest current value and 0xFF is the largest. Subtrating rgb from 255 would invert it.

2. I have developed my own software to control the current. I have tried to call DLPC350_setLedCurrent (54,54,52) and it failed to project sequences. I have done an experiment on this and found out that if the function parameters are lower than about 60, then DLP4500 won't works. Why is this?

Thanks.

  • 0
    TI__Mastermind 23070 points

    Hello Raymond,

    We will look into to code and get back to you.

    regards,

    Vivek

  • 0
    TI__Genius 10925 points

    Hi Raymond,

    1. Can you explain why does it need to subtrate the current value from 255? As to what I understand, 0x00 is the lowest current value and 0xFF is the largest. Subtrating rgb from 255 would invert it.

    TI> This action depends on the InvertPWM parameter. This can be set/read using the USB Command function DLPC350_SetLEDPWMInvert() / DLPC350_GetLEDPWMInvert(). 

    2. I have developed my own software to control the current. I have tried to call DLPC350_setLedCurrent (54,54,52) and it failed to project sequences. I have done an experiment on this and found out that if the function parameters are lower than about 60, then DLP4500 won't works. Why is this?

    TI> Kindly give me some more time to check on this.

    Thanks & Regards,

    Hirak.

  • 0 in reply to Hirak Biswas
    TI__Genius 10925 points

    Hi Raymond, 

    After experimenting with the LED values I found that the LED Currents on my evm works fine down to 30, after which they start to flicker not being able to get enough current. This value may change depending on the LED manufacturer, models even process variation. There seems to be no controller/programming error.

    Thanks & Regards,

    Hirak.