At the end of our PCB assembly line is this NeoDen Ion-6 reflow oven. PCBs ride through the oven on a belt and get deposited into this tray where we can collect them. There's just one problem though, if a panel sits in the tray for too long, it can block the following panel from exiting the oven. And that's obviously a bit of a risk because it means that a panel could get overcooked and destroyed.

In large production lines, this problem is solved by using automatic unloaders that pull the panel out of the oven. And if we upgrade our oven, we'll look into that as well. For now though, we explored lots of ideas like chutes, ramps and belts that would carry the panel away, but none of them really inspired much confidence and would likely take up more space than we have available. The best solution we could think of is this simple proximity alarm made up of a sensor and a buzzer and some programmable logic like an Arduino. I'll show you how we made this one.

These proximity sensors are great. You can tune their sensitivity from a dial on the back and an LED shows the output status making them really easy to debug. I started by gathering a proximity sensor, a buzzer, an LED and assembling these onto a ProtoShield. The sensor gets its own 3-pin header. I already tested the sensor at various heights and angles over the output tray, so I was confident it's suitable for this project. The only thing you really have to look out for is direct reflectance from the tray, so it's best to mount the sensor at some angle.

Next, I cut this acrylic bracket to hold the sensor. You can bend acrylic by heating it, which makes it great for prototyping these compound angles. First, I bent the bracket about one angle that I wanted and then twisted it to create the compound. Really straightforward. To mount the bracket, I included these deep etches to locate some magnets and they worked out as a really pleasing press fit.

Next, I whipped up some code to make the alarm work. If a board is detected, then you get a single beep and a flashing light. If the board stays there for a while and isn't removed, then the beeping just becomes a bit more insistent. Now it's time for a dry run. Everything seems to be working as intended. I placed the panel in the tray and the alarm gives a beep and a flash. So the proof of concept works. We're almost done. I just need to find a suitable enclosure for the circuitry. Something to keep out dust and add some protection.

I didn't have any enclosures on hand that would accommodate an Arduino and a protoboard on top. I could have 3D printed something, but to design and print something would at least take a couple of hours. And this is meant to be a really quick project. Like the whole thing in less than a couple of hours start to finish. I wandered around the warehouse a bit looking for some inspiration until I spied the form box. This is a vacuum form tool. I've never used one of these before, but let me tell you it was a pleasure. I had a custom enclosure in seconds and it's pretty mesmerizing to watch. By positioning the project a little off-center, I left some material on the sheet to cut out and use as a back piece. To attach the back piece, I just heated the edges of the form and bent them around by hand. All that remained was to carefully cut out holes for the connectors and buzzer. I left the LED covered to give it this nice diffuse effect. A couple more magnets and some double-sided tape and we're done.

Now you could likely connect one of these sensors directly to a buzzer and call it done. You would have an alarm whenever the sensor is active. That would first become a bit annoying though, I think. We didn't want this workplace to be the kind of environment where there's alarms going off everywhere all the time.If that kind of alarm is what you're after for your own project, then that's potentially an even simpler solution that doesn't require any programming.

We release these factory videos every week to give you a peek into the PCB assembly process and the various side projects that crop up from time to time.

If you have any specific questions or think we should discuss a particular topic, we'd love to hear from you in our forums. Links below.

Thanks for watching.