This is an expansion for my previous grow light installed in a used PC chassis. It has four channel PWM dimming for far red, red, blue, and white LEDs. Being able to control the colour mixture mixture means that you can control the root growth, leaf growth, and other properties of plants.
If you built the older grow light and are expanding it with this one, you don't need to wire the power on signal line again.
Step 1: Drill and Tap the Aluminum Bars
Drill the flat bar for attaching to the PC case.
Drill the heatsink for attaching the fan, circuit boards, cable ties, and stands.
Step 2: Drill the PC Case
Remove the previous grow light before drilling. Drill the case for the screw holes, cable ties, potentiometers, and wire bushings.
Avoid getting metal shavings into the power supply or any of your circuit boards.
Step 3: Attach Flat Bar to the PC Case
Step 4: Install LEDs on the Heatsink
Epoxy was used to attach their base plates.
Their anodes were connected together to the PSU's 12V.
To save space on the heatsink, you can use multi-LED base plates or smaller footprint LEDs. I used the LEDs ordered from eBay.
In this picture, 12 deep red LEDs, four red LEDs, eight royal blue LEDs, and four white LEDs were installed. The far red LEDs weren't installed yet. Their positive and negative connections were wired. It should consume around 60 watts.
Step 5: Four Channel ATtiny84 PWM Signal Source
The PWM outputs were connected to PWM inputs of the LED drivers. W1 through W4 were connected to the four potentiometers.
For more outputs, you can use a microcontroller with more PWM outputs or use switches for the extra outputs.
Step 6: LED Driver
One driver was used for the far red LEDs, four for the red LEDs, two for the blue LEDs, and one for the white LEDs. Their ground wires can be connected together. For drivers that share the same PWM channel, connect their PWM inputs together.
I used this LED driver: https://www.instructables.com/id/Power-LED-s---sim...
Step 7: Install the Fan and LED Drivers
I used crimp connectors so that the expansion grow light is detachable. If you want, you can heatsink the MOSFETs.
Step 8: Install the Potentiometers
Step 9: Install the Four Channel PWM Signal Source
The 5V input was wired to the PSU's red wire and its ground was wired to the black wire.
Step 10: Install an Inline Fuse to the 12V Wire
Step 11: Install the Plastic Cover and Light Shield
Install the plastic cover over the driver boards.
Install the light shield for eye protection. You can use aluminum tape to reflect the light.
Step 12: Using the Grow Light
Set it on a timer for a light-dark cycle. Different plants need different light to dark ratios. You can use a 3-terminal outlet timer so that you don't need a second power supply.
Adjust the intensity of each wavelength through the potentiometers.
If your plants need more light, you can move them closer to the light, add lenses, or use aluminum foil as reflectors.