In this project I have made exposure box for my PCB manufacturing with photolitography process. For exposure light I’m using 20W LED floodlight which is actually intended for outdoor use and works on 220V. I choose this floodlight because thay are very thin, which is perfect for use in the exposure box. Electronics components are powered by pre-made power supply that can provide 12V and 1.2A.
Here is YouTube video in which I have explained the whole process of making this project.
Brain of exposuring box is microcontroller PIC16F886. Display segments are attached to the port A, and multiplexing is done by pins 4, 5, 6 and 7 of the port C. Corresponding segments of all displays are connected together, and each display can be turned ON by low power NPN transistor switches. Displays are with common anode, so when we send HIGH signal to the base of the transistor, corresponding display will be connected to the VCC.
Buttons are attached to the first three pins of port B. I have attached buttons to this port because this MCU has internal weak pull-up resistors on this port which state can be controlled by the code. Beside that we can configure this MCU to make interrupt on every detected change on this port.
Piezzo speaker is on pin RC2 and it is driven by PWM signal streamed into NPN transistor. LED for pulsing one second is on port RB7 and relay for exposuring light is on port RB6. When we raise the level of this pin, NPN transistor will activate relay, and exposuring light will turn on.
Voltage for whole circuitry is nicely regulated with 7805 regulator which gives 5V on its output.
Dimension of PCB are 87 by 47 millimeters, and it is one side PCB completely made on the top layer.
I have decided to drew the whole PCB on the top side, because I have found interestingly small SMD displays which I have decided to use in this project. All others components are mostly SMD type as well.
Here are some images in time of making PCB:
Because PCB, exposure light, power supply and all other components goes into plastic container, I have designed internal box that has the purpose to hold the PCB above the exposure light. For designing 3D model of this box I have used Sketchup.
Dimensions of the glass is 12 by 17 centimeters and it will lay down directly on the walls of the box. Because this box is smaller than the plastic container, I have added spacers on the bottom to make the box centered with the container. Whole internal box have been made with 3mm thick cardboard.
Previous images represents how the final product looks a like.
Front side of the box can maybe be a little bit cleaner but it’s ok for my needs. I already have made couple of PCBs with this exposure box and it works perfectly.
For the exposuring with this box and especially with this type of exposure light (20W LED floodlight), it usually takes about 12-15 minutes for full exposure.
Software
Software for PIC microcontroller has been written completely in C, and I have used mikroc IDE from Mikroelektronika. Code and everything in this video is open source and it is published on my GitHub profile.
For display multiplexing and buttons debouncing I have used internal PIC timers. It’s very interesting approach so I suggest you to check out the code.
GitHub Repository
Summary
The realization of this project was very useful for me because in addition to the fact that I now have my own exposure box, I learned a lot of new stuff in the fields of PIC microcontrollers and PCB designing.