how we made the controller case

I’ve been nurturing the idea of developing my own air handling unit controller for a long time now. For all the time of work in the field of automation and dispatching of engineering systems, a decent experience and understanding of how it all should work and look has been accumulated. There were already quite a lot of solutions on the market with different approaches and in different price segments, but with the departure of Western brands, there were significantly fewer of them, and this is one of the reasons that prompted us to take the first steps in the development of the controller.

At the end of 22, I started working in this direction. The plan was simple: first, we will only design and render the future device. If you like the result and you manage to embody all the ideas in the render, then you can take the following steps, and if the result is not very good, then you should not continue.

I wrote a short spec and “sketched” in Figma how I see the device, after which I discussed all this with a designer who specializes in industrial devices and with whom I already knew. The terms of reference described the main points of the controller: control of only one push knob (an encoder with a button), functional illumination under the knob, display 2 – 2.4 inches, monochrome, form factor for a modular shield, quick-clamping and quick-detachable terminals, dark color.

Here you need to step back a little and tell in general what it is, why and why it is so. Any ventilation installation (and in the future not only ventilation, but pumping stations, air conditioners, lighting, etc.) cannot work without automation, there must be a controller that will turn it on, regulate it and make sure that everything works as it should. All controllers can be divided into two classes: freely programmable and parameterizable. The first are PLCs, which can be used in general, anywhere and in any way, for this you need a programmer with a laptop, he will write a program for him or take something ready-made and will set up and run all this for some time. The second ones are not so flexible, they are made for standard situations and do not require a programmer. I chose the second option and will try to make a comfortable user experience. The functional lights below the knob will have different colors and will likely be segmented to indicate different situations. Controlling one knob from my experience is the most convenient option, more convenient than buttons and, especially touch buttons (hello Carel). The screen is color and non-touch, and colors will hardly be used. In the original version, there was an idea to make a mini line display inside the knob, where it would be possible to display the current temperature and setpoint values, but this idea was abandoned almost immediately, as this significantly complicates and increases the cost of the entire device. And, of course, a site where you can configure the desired program, download all the diagrams, drawings, instructions, tables, etc.

The whole development process of the case can be divided into several stages.

1. Pre-project research, collecting references.

2. Sketches, choose a starting point.

3. A couple of concepts, we choose the final direction.

4. Design, rough 3D model, beautiful rendering.

5. Preparation of design documentation, which already takes into account all the iron, boards, fasteners, dimensions, etc.

6. An intermediate model, we print on a printer and paint, we collect everything, we see if everything converges.

—- now we are here —

7. We make changes and roll out all the documentation, send it to production.

First stage – this is a selection of references and geometry. At this stage, the designer makes a selection of different styles, objects, devices in order to decide on the concept, shapes, lines, etc.

We decided to use simple forms based on primitives. Complex lines and curves were considered unnecessary.

Next, the designer prepared sketcheswhere the geometry and shapes are already defined, and it was necessary to choose the most successful layout, front panel and backlight option.

We settled on the last version with recessed backlighting and sectors. The name of the future Eleven controller has already appeared here. The working title stuck and will most likely stay.

On next step it was necessary to determine the location and number of terminals, with ventilation holes and ports.

Two different concepts are presented here, which differ primarily in the arrangement of the terminals. Both options have their pros and cons, but settled on the first option with a frontal arrangement. This will save some space in the closet and add convenience during installation. And yes, it looks much better.

Now on design stage there are no more questions, it remains to prepare the final render and you can show off.

Here you go half way passed. Here it was necessary to make a decision whether to move on or not. I was pleased with what we got at this stage, although there were a few questions left. For example, how bright the backlight will end up being, there are fears that the whole backlit idea is not viable.

We took a short break and then proceeded to second stage. Here, joint work with a circuit engineer was already required. For a long time we selected all the components and datasheets for them. The screen size was originally chosen as 2.4 inches, but it turned out to be too big, so they reduced it to 2.2 inches. Quick-clamp terminals were replaced with similar Chinese ones, they are green, not gray as in the design. They are also a few millimeters larger than the original ones, because of this it is necessary to slightly increase the case.

In Chip and Deep I bought a handful of different encoders and a plastic twist to find the most responsive. We made several different versions of the lens, one completely recessed with a diffuser and the second version protruding slightly from under the twist. We are currently testing both options. In parallel with this, boards were designed and ordered. In general, this stage turned out to be quite long and complicated, it was necessary to take into account many nuances so that all this would eventually assemble, snap into place, work and not get warm.

This is what the render looks like design model, where all the elements are selected and stand in their places. Can be distinguished from the design by the molding holes.

Now we have printed the model on the printer and painted it black. We solder the boards and put everything together. At the same time we write software. After all this snaps into place, we will twist, look, make changes to the case and it will be possible to give it to the manufacture of the first batch.