I need to provide uniform intensity or uniform spread of light using this LED in a particular area(Small region). I have read about diffusers such as engineered diffuser, ground glass diffuser, Light shaping diffuser etc. Which is good for my project? Which diffuser can provide highest efficiency?Small region means the dimensions are length x width x height : 5cm x 5cm x 3cm(rectangular box). Sample is placed at the bottom centre of the box and led is placed 2.7cm away from my sample at the height of 1.5cm
Electrical – LED uniform lighting
ledled stripled-matrix
Related Solutions
In general this sort of symptom happens when you have a floating input. This suggests that there's some input, probably to the 595's, that you think is connected but isn't. Could be on the Arduino, if it's something the Arduino code is waiting for. Could even be a wire that's connected, but the Arduino code forgot to set that pin to output.
Three issues.
Your schematic is wrong for the setup you want. It should be wired GPIO to Gate, LED Cathode to Source, and Ground to Drain. You correctly have the 12 Volt supply ground tied to the RPI ground. See @Daniel's answer for the correct schematic.
Even with the right schematic, you have miswired the mosfet. The BUZ91A datasheet says its left to right Gate, Drain, Source. Your extta picture shows its currently wired as Drain, Gate, Source, explaining the behavior of 50% on when the GPIO is 3.3V, 100% on when GPIO is 0V. I'm shocked your RPI hasn't been fried, as using the GPIO as the Drain on 12V would mean all that voltage and current goes through your RPI's cpu.
- Once you fix the wiring, you may see that the mosfet won't turn on all the way. The datasheet shows that it's Voltage Gate - source Threshold is 3V typical, 4V max. Meaning that it may barely work at the RPI'S 3.3V level. That Mosfet is not well suited for 3.3V logic level applications. At 3.3V, the FET won't even pass fractions of an Amp. You made need a driver, see below.
If you want to stick to that mosfet, and you haven't somehow fried your RPI or the Mosfet, then you could use a NPN transistor as a driver. A 2n3904 or 2n2222 or any similar. It's not critical, it's just a switch. Logic will be reversed, so on the RPi, A logic High/3.3V will turn the leds OFF.
simulate this circuit – Schematic created using CircuitLab
Best Answer
I don't believe that uniform light intensity within that rectangular box is possible with only one LED. If I would have to do it, I would try a box made from special frosted plexiglas lighted by an array of LEDs outside with a distance of about 1 cm from each LED to the next LEDs and a distance of about 1 to 2 cm to the box. Of course each side of the box should be lighted with an array of LEDs.