Designing My First Electronic Board to Safely Play with Lasers.
Coming from Biomedical Engineering background, I joined Apparatus as an intern hoping to gain fundamental skills in the field of hardware development. Although my work is unrelated to Biomedical Engineering, I believe working for a Medical Device company won’t be much different. At the end of the day, it’s mostly about hardware and software when it comes to engineering products.
At the start of my internship, I was told to design a functional module for the Atomotion controller. Having zero experience with controller boards, I started off by playing with an Arduino to understand the basic working of such devices.
My experience with electronics has been very limited. I’ve only designed a fully functional Pulse Oximeter device for a project. It was a simple design where the circuit was connected through wire wrapping instead of on a PCB board. So naturally, I found the task of designing a PCB quite daunting.
The first phase was finalizing a particular function for the module. After doing a lot of research and discussing with my team, I decided to design a module for a Laser cutter. The Lasersaur Laser cutter inspired me to design a driver that includes a hard-logic safety circuit, making laser cutters safer to use. I felt that it would be nice to have another driving circuit for a simple Laser Diode that could be used for light cutting and etching. Unlike the bulky CO2 lasers, laser diodes are small enough to easily mount on the machine.
The information provided by Lasersaur was extremely helpful in designing the hard-logic safety circuit. The only issue was hard wiring all the Limits, Doors and Chiller sensors on the module. The Lasersaur controller board had enough space to accommodate several RJ45 connectors. However, the module in Atomotion was not big enough to place such big connectors. Therefore, in my design, limits sensors are wired through the controller while the 2 doors and chiller sensors are hard wired. As there are basically 3 connections with the door sensors and 2 with the chiller, I replaced RJ45 with 3-pin and 2-pin connectors.
Laser diode driving circuit took me quite a lot of time to design, although it turned out to be quite similar to the LED driving circuit I made for my Pulse Oximeter. And naturally, there are more than one way to design such circuits, so I chose the design that’s simpler, cheaper and makes more sense to me.
While designing the two circuits, I realized that it will be nice to give the user an option to run their Laser PSU by either Pulse Width Modulation (PWM) signal or analog signal. Therefore, I used a two channel digital potentiometer for the Laser driving circuit and to drive an analog signal for the laser.
During the whole process, I simultaneously worked on schematics and comparing the components with the module layout. It might appear to be a lot of work but it’s necessary to be familiar with the PCB layout and the number and size of components and connectors it can accommodate. Since my module includes a few and basic components, it turned out to be much easier than I anticipated. My module doesn’t require a microcontroller so even setting up the track layouts was pretty straightforward.
It took me around three weeks to finish the whole module, which may appear to be quite a long time for a simple module, but as a novice in electronics and using KiCAD for the first time, I was satisfied. It is amazing how much you can do within a function module. There’s a lot of power and I/O pins provided through the OpenCNX connector which opens up a lot of possible circuit designs that design can support. In fact, if you notice the schematic, I did not use most of the connections from the pins of the OpenCNX connector.
This whole experience reinforced the idea that if you start doing something with minimal experience and maximal interest, it’s possible for you to accomplish your goals. I personally feel a lot more confident dealing with technical stuff, and it made me want to pursue this field in more depth. I feel like it’s not that hard for me to design other modules, such as stepper drivers, thermal drivers, feedback system, etc. As a matter of fact, after finishing this project, I’m really curious to try using Atomotion to develop 3D bioprinters.
A detailed step-by-step tutorial will be available on OpenCNX Github Wiki.