I made this to replace my old exposure unit. This one got internal timer and real UV leds. Main material is 20mm MDF. Electronics are controlled with arduino nano. Even if you are not interested making own PCB's or stuff like that, you may find usefulI tips when working with MDF. Entire making of process is documented in video below.

Step 1: Making of Exposure Unit

Any comments and questions are welcome :)
https://youtu.be/wRdey0U7HZM

Step 2: Technical Info

Schematic is a mess but basically I made simply expansion shield for arduino nano where you plug all the wires, pullup/down resistors, buzzer, terminals, FET etc... That external 5v regulator is not needed if you use arduino's build in regulator.

Glass panel inside unit is from old scanner. That determines my box size.

R1 and R7 are 10k pulldown resistors.
R4 and R6 are ~ 200ohm current limiting resistors for led and lcd backlight.

Both trimmers are ~5k. I think you can use any other values too. LCD brightness and voltage to FET gate are controlled with them.

Caps are for smoothing purpose for regulator LM7805.

C2 1uf-10uf
C1 0.1uf

FET IRLZ44N or similar logic level fet. This one is bit over kill but i had it laying a round.

To potpin I attached multiturn 5k pot. If you are using my code I recommend using multiturn pot because accuracy is much better compared to normal pot.

PAD1 and PAD4 are meant to be connected via jumper wire.

PAD2 and PAD3 are meant to be connected via jumper wire.

Piezo is 5V Continuous Sound Piezo Buzzer. I Dont know exact part number. Bought from ebay.