A friend told me that they got a 3D resin printer, and they do not want to spend the money to buy a UV cure chamber. Resin printers produce solid objects, but the resin hasn’t cured, which means the prints are structurally weak. To bring them to full strength, you have to clean them and then put them into a UV cure chamber, where the UV light causes the resin to cure. My friend told me that there are YouTube videos (1, 2) that show how to make your own cure chamber, so I thought I’d help my friend out.
Unlike my other projects, where I start the project with a vision of what I want, this one was for a friend. Since my friend wasn’t very familiar with electronics, they could not give me the specifics of what they wanted in the design for the UV cure chamber. Therefore, I thought it would be best to go straight to prototyping and get feedback as early and often as I could; that way, I can get them a system they’re happy with, even though I couldn’t flesh out the design before starting the project.
For my first design, I wanted to use the Stampduino as the heart of the system and hook it up to some buttons and an LCD screen, similar to my reflow oven project. The buttons would allow you to turn some UV LEDs on and off as well as set their brightness. I figured the easiest way to control the UV LEDs brightness was by driving a PWM signal into a NMOS transistor that goes between the UV LEDs cathodes and the system ground. But what UV LEDs should I use? Well, my friend told me that the 3D printer was a Anycubic Photon, which uses 405 nm wavelength UV light for curing. I used this info to order a UV LED strip (I’m not sponsored); I picked this one because it has a higher power rating than most other strips on the market, and is waterproof (in case the resin prints are wet). The LED strip conveniently comes with a 12V, 60W power supply, which I’ll use to power the project. I dug through some past projects and found a beefy transistor which would work for my purposes. I then wrote a state machine interface very similar to the reflow oven code, and demoed it to my friend.
I showed that you can set a timer, which controls how long the UV LEDs are on for. My friend requested that I add a speaker so that once the timer is done, the system beeps, alerting the user that the cure has finished. Funnily enough, the speaker circuit is nearly identical to the UV LED circuit: an 8Ω speaker that is tied to ground through an NMOS transistor. This transistor is also driven by a PWM signal, but the PWM wave is actually just a convenient way of creating a square wave, which causes the speaker to create a constant tone. The three differences between the UV LED circuit and the speaker circuit are (1) the speaker is pulled up to 12 volts through a 100Ω current limiting resistor while the UV LED strip connects to it directly (though I’m sure there are current limiting resistors built in to the strip), (2) the speaker has a fly-back diode since the speaker is an inductive load, and (3) the transistor for the speaker is much smaller than the LED strip since the speaker will draw less current than the whole LED strip. The setup for the final prototype is shown below:
The photo above shows I only used a small section of the LED strip for prototype purposes. The next step is to move the project into a form-factor that works for my friend.
EE Diary 