Alternative to digital Potentiometer?

Forum|Forum|6 years ago
September 16, 2020
6 replies
1761 views

I have to control several LED signals via PWM (up to 16), whose voltage and current can be above the max 5v tolerant and 20-25ma max current GPIO pins. These LED's can change and are not constant. Meaning they have different voltage and current requirements.

Was already using a digital pot with boost converter to handle the voltage requirements. But for sourcing was thinking then using a BJT to control each led, but because the led's can change, they require different resistor values attached to ground, so digital pot seemed like I good fit but to have 16 digital pots would mean I need 18 lines to control the digital pot (If SPI) and another 16 for PWM, is there another alternative to this setup I propose?

TIM

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TDK

Digital pots have limited current capacity. Be sure you don’t exceed that.

there are a lot of constant current LED driver chips out there. I would use one of those instead.

I2C would be better than SPI here if you go with digital pots.

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BazeAuthor

Associate II

Thanks so much! This really helped a lot. @TDK why would I2c be better in this case?

Danish1

Lead III

With SPI I guess you're thinking of a separate select for each pot. I2C devices can often have different addresses, often pin-selectable.

But you don't need a separate select for each SPI device. You could mount several in series and clock the data to that group of them in order.

Or, as old-timers like me will remember, you might use the modern equivalent of a 74LS138 to have 3 "address" lines to select which of 7 or 8 SPI devices you next want to select.

Regards,

Danish