alex_c
Posts: 2
Joined: Sat Feb 10, 2018 11:55 am

Toggling Waveshare LED boards

Sat Feb 10, 2018 12:01 pm

Heya (:

I‘ve been using Raspberrys for a few years now, but only for software stuff. My understanding of electronic components is quite limited, until yesterday I didn't even know what a transistor is, but I'm trying to get into it and it looks like fun.

However I'm kind of stuck here and hope that someone is able to clear up some things :-) TL;DR is at the end.

I have a Waveshare IR-Cut Camera (https://www.waveshare.com/wiki/RPi_IR-CUT_Camera).

The camera comes with two LED Boards (I think it's these ones https://www.waveshare.com/infrared-led-board.htm). The boards do have a light sensor to adjust the intensity of the IR LEDs. The problem is that these boards are powered even when the camera is not in use and therefore get incredibly hot, even after glueing heatsinks to the back. They get so hot that you cannot touch them anymore, which worries me. Since I only need them every once in a while to take a photo, I'm trying to turn them off when not needed.

Since the boards are powered through the camera board which is powered through the CSI port of the Pi, they cannot be turned off. My first idea was to simply power them through a GPIO pin which could be toggled through software, but apparently they use too much power (AFAIK those are 3W LEDs) for a GPIO pin (viewtopic.php?t=152426#p999293).

So my next idea was to make a "simple" circuit to power the LEDs from the 5V output of the pi and use a transistor connected to a GPIO pin to turn them on/off (like this one here: https://www.raspberrypi-spy.co.uk/2012/ ... utput-pin/). However I cannot find a datasheet for the LED boards, therefore I have no idea what kind of power they actually need. All I was able to find is that the screw hole next to the photo resistor needs to be connected to the VCC (3.3V) and the other screw hole to the GND. So I have no idea if that circuit would supply enough current.

A friend suggested that instead of using a 5V output from the Pi, I might be able to solder a transistor between the camera board and the LED board. Since the camera board obviously already provides the correct current and voltage for the LED board, I should not have to worry about that stuff anymore. Correct? Would soldering a NPN transistor between the LED board's GND screw hole and the camera's GND screw hole and connecting the base of the transistor to a GPIO pin work? What kind of transistor would I have to use?

TL;DR: I want to turn on the Waveshare LED boards (https://www.waveshare.com/infrared-led-board.htm) only when I need them. How to? Would soldering a NPN transistor between the LED board's GND screw hole and the camera's GND screw hole and connecting the base of the transistor to a GPIO pin work?

alex_c
Posts: 2
Joined: Sat Feb 10, 2018 11:55 am

Re: Toggling Waveshare LED boards

Tue Feb 13, 2018 1:17 pm

So I tried my luck today and built the following circuit on my breadboard. I used a BC517 because of the high gain and because it should be able to handle the high current (if needed, but since there is no datasheet for the IR boards...).

At first I went with a 22k base resistor, but the LEDs didn't work. I then tried various resistors down to 1k, but still nothing.
Screen Shot 2018-02-13 at 14.15.18.png
Screen Shot 2018-02-13 at 14.15.18.png (101.66 KiB) Viewed 112 times
Any help would be greatly appreciated.

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