Integration of Electronics

Who at some point has never faced the situation in which you developed a PCB and there is no way to have it fixed in a housing or nice looking enclosure? That is why it is really important during development phase to keep contact all the time with the complete product development team which in this case use to be the Mechanical team to come all together to the same understanding and don't reach a dead end in which the already developed PCB cannot be placed in any feasible form.

We, electronics engineers tend to work moving forward-thinking on the PCB, how to be able to place all the components and using the shape or outline with which it is more comfortable for us. This is especially complicated or dangerous if we need to incorporate batteries to the product, since batteries are in really limited shapes, so the flexibility we have to select the shape of the enclosure is even lower.

Last week I posted a small and simple PCB I was doing for a Touch Sensor, while I was designing the PCB, I had the CAD software open at the same time to take a look at which possibilities I had to be able to enclosure this PCB into "nice" housing.

You have the limitation, first of budget, since this is a private project there is no way to have some sort of flexibility to have with you deal with big projects since development of custom parts and acquiring some others is really limited. And the second limitation is tooling.

Basically, the body has been machined from Aluminum, due to the fact the entire body cannot be conductive otherwise if you just touch it the sensor will recognize it and switch on the light, it is required an isolator between the area which is going to act as the real sensor and the body. For this is used the POM ring you can see in black color in the picture, this ring is isolating the round Aluminum part which is on the right side, acting as the real sensor. Another constrain to take in account is the clearance we have between the body and this sensor, since if it is not enough the capacitive effect will be transfer to the body not having the result we wanted.

On the body, I decided to don't use screws in order to make the assembly easier and also due to size constrains since it would limit a lot my PCB shape and also the body design. So basically there are some ledges which will hole the PCB in place. The back part is open, and it has a thread to be able to place a cap to close it and openings on the sides to place grommets to guide the cable trough and avoid damaging the cable.

The cap has same thread and two holes added, these holes have two purposes, one of them is being able to close the cap tightly with a tool and being able to open it and the second purpose is to be able to fix the switch in case needed since they are M3 threaded. Also included a small counterbore to be able to glue a magnet in case needed.

The grommets I found them as standard part online, so as mentioned at the beginning of this post I decided to base the design thinking on which constrais did I have and finding the suitable grommet was one of them since I could not go to custom shape, so I needed to adapt an existing one.

Once the housing is ready, we can check if everything fits together, so as you can see in the picture above, the PCB enters into the housing and cables are soldered in place. I must admit that it is not the best design for "mass" production due to the fact several steps could not be automated, and fixing the PCB on the housing together with the cables was not the easiest task and this another boundary you need to think about when you are defining a product since it is not the same to assembly few units than thousands, another thing to keep in mind, keep your manufacturing team always close to you, they will be painful in some situations :) but at some point really helpful to avoid future issues.

Another challenge I needed to solve was how to press or keep fixed the PCB into this housing, due to the fact the cap is Aluminum cannot touch directly the PCB I needed a part which is plastic or something is not conductive. After thinking a bit about it, I decided that the fastest way would be 3D print a small ring which is acting as spacer and will pressure or hold the PCB once the cap is in place. I could do this like I did the other plastic ring, but again, thinking about making things simpler, this part is not going to be seeing, so does not need to be perfect and making this manually would take a lot of time, so let's go to 3D printing.

Now we are almost ready, we just need to close the back cap, which as said has 0.5mm pitch thread, using a tool which allows you to turn it, otherwise with the bare hand would not be possible, and we have our Touch sensor ready

This article tries to show, how even a simple project, can include several challenges which can be resolve in different ways, but most important thing is to never lost the big picture, this was done by a single person, but in a big team is not so easy to take in consideration all the boundaries which we are going to have or face. We tend to finish the part in which we are involved without take a small break and thinking together, which is the best way to achieve the final goal, avoiding having a big blockers and issues during the development.