What pins are best to power custom LED shield?

OpenMV Boards
1

Hi there,

We are developing an LED module with relatively high-power LEDs (max. forward current about 1A) that is activated and powered by the RT1062 R4 (and later we will use the N6).

At first we wanted to use the VIN pin to power the LEDs but it turns out we prefer to power the board with a lithium battery connected to the JST port (to be able to recharge it with the openMV). Thus we are left with the 3.3V rail and the RAW pin to power the LEDs, and both work, as our circuitry still limits the current to 350 mA.

Should we rather use the 3.3V rail or the RAW pin to power the LEDs?

I see the RT1062 pinout diagram mentions “1A supply max.” but in the details it says “Do not draw more than 250mA from your OpenMV Cam’s 3.3V rail”… I also noticed the light shield uses the VIN for power, but the PIR shield seems to connect to all the other power pins.

2

You can draw 1A through the 3.3V regulator; I do this for the PIR shield’s LEDs. We just say not to draw more than 250mA since we don’t want folks generally overloading their cameras. After 1A of load, the camera will start to buckle. The regulator is designed for 3A. But, generally, brownouts happen after 1A of external load.

The benefit of RAW over the 3.3V rail is that it can probably do more current, but it doesn’t turn off in deepsleep. So, if you are doing low-power stuff, it’s less helpful. If not, then use RAW. That said, RAW is not at 3.3V. It could be 3.7V or 5V, and etc. So, harder to use unless you design things right.

1 Like
3

Thanks for the clarification Kwabena!