ECG Patiënt Simulator - The housing.


De volledig afgewerkte behuizing

The finished housing.

The 3D Printed housing.

At first I chose for a transparent Plexiglas housing that I would cut on the laser cutter. Because our makerspace "The STEAM Reactor" is still under construction and therefore has no accommodation yet, no laser cutter is available, and because our local FabLab is still inaccessable due to the prevailing Corona pandemic, we have to use the 3D printer.

To make the reproducibility of this project as easy as possible, I chose to make the housing in 3D printed PLA material. Due to its compact size, it is possible to print this box even on the smallest 3D printers.

This housing should provide space for all components and still be as compact as possible. In order to keep the footprint small, so that my little Velleman Vertex Nano 3D printer could print this housing, I had to position the 9V battery on its side, which makes the whole thing a little bit higher. The final outer dimensions are: 7.7 cm wide x 7.9 cm deep x 4.3 cm high, grabber clip connectors included. Small enough to fit in the pocket of an operating room suit.

This device consists of an orange top half with the necessary recesses for the push buttons, the grabber clip connectors and the inscriptions, and a yellow bottom half in which the 9V battery, the speaker and the PCB are attached. Furthermore, there are the support inlays in white PLA on which the grabber clips and the electrode labels are attached. The inlays for the waveform sign and the text labels are 3D printed in transparent PLA. The top and bottom halves are attached to each other with four 2mm metal sheet screws.

To make the 3D drawing for this housing, I chose Design Spark Mechanical by RS Components. This program can be downloaded and used for free. Only a minor registration on the RS Components website is needed. Design Spark Mechanical is one of the few free 3D design programs you can download and install and then use off-line. Most other free 3D design programs can be used online without installation, so there should always be a good internet connection around if you want to draw. Here on our STEAM Reactor website you can also start the software download of Design Spark Mechanical.

I made separate .STL files for each part of the housing. You can download these files if you want at the downloads area of this project. If you use an adult 3D printer, and not a mini-model like I did, you can easily slice all parts together into one .gcode file and have them all 3D printed in one go. For the transparent inlay parts such as the waveform and the text inlays you have to generate a separate .gcode, unless you are the happy owner of a dual-head or multicolor 3D printer. Anyway, everybody should be able to make this enclosure, so with a separate .STL file for each part you can go anywhere.

The biodegradable PLA material is available in many colors. So everything is possible. The fresh colors I chose will definitely draw anyone's attention.

The grabber-clip-connectors.

To fix the grabber clips there are undoubtedly clips that are commercially available. However, my search for these clips were no success. A helpful medical equipment technician offered me some grabberclips of an old and malfunctioning simulator he had at home.

I would leave the other makers on their own if I were to finish my own ECG Patient Simulator with these clips without looking for a universal solution.

De drukknoppen, bevestigingsschroefjes en soldeerhulp.

And the solution came:

At Veritas, yes Veritas, the mecca of many Maker Lady. And now I sincerely make a deep bow out of respect for the making woman, because a lot of women still think they don't belong in a Makerspace or a Maker community. Hereby, a more than welcome for the making woman.

Anyway, as a guy on a woman's territory, I was given fantastic help by the saleswoman of the Veritas in Genk. After a short explanation of my needs, the saleswoman led me, through a maze of life-threatening needles, threads and for me still undefined tools, straight to the shop rack, where all the buttons hung as we know them from blouses, pants, jackets and other items of clothing. After a more detailed description with a lot of gestures, the saleswoman was able to hand me, without the slightest hesitation and in one smooth movement, the 10mm Prym branded push buttons with item number 390107 and the name Jersey. Yes, this was surely a massive product knowledge? Some DIY shops could take this lesson. The grabber clips of an ECG cable fit perfectly on these push buttons.

Of course, such a push button is not intended to be screwed onto a plastic housing. So a solution had to be found for this too.

Such a button shows out to be very good for soldering. So I soon came up with the idea to push the head of a small bolt of M2 by 10mm in the opening at the bottom of the push button and then soldered it. With a construction of my mini vise and the clamp of a half disassembled 3rd hand, that I use for soldering work, I made  a tool to keep the screw straight in the push button during soldering.

In the front panel of the housing some recesses for the push buttons have been made. These are the same distance apart as they are on the printed circuit board. It suffices to provide a small elevation on the printed circuit board by means of some female pin connectors and plug in the push buttons. As a result, they protrude above the other components on the PCB and are just high enough to pass through the front plate. The push buttons are almost flush with the front panel. This prevents them to be operated while in your pocket. They are still easy to press however. The LED is located on the PCB between the two push buttons. This corresponds to the position of the waveform inlay of the front panel. This causes the waveform to illuminate due to the LED.

When assembling the housing, care must be taken not to tighten the screws, with which the housing is fixed together, too hard. When using PLA, which is a fairly soft material, the screws could break the screw thread. The use of ABS as a printer filament gives a firmer result, but is not environmentally friendly.

The grabber-clip connectors that are above the battery on the inside of the front should be electrically insulated. If the metal casing of the battery touches these terminals, they can be shorted. This will not damage the circuit, but it may prevent the simulator from producing an ECG signal at the grabber clips. I used a drop of hot glue from the glue gun for this. I also glued the speaker to the rear case with this glue.

I fixed the inlays for the texts and the inlays for the grabber-clip connectors with some super glue.

I made the electrode names with self-adhesive round stickers in the colors of the grabber clips together with self adhesive letters, both from the "pickup" brand. (Round stickers 8mm set of 6 colors = Pickup Item No. 9059. The red letters 5mm = Pickup Item No. 01322005 and the white letters 5mm = Pickup Item No. 01312005). To prevent the sticky letters and round stickers from coming off, I sealed them with some transparent varnish. You will notice from the image of the front of the box that the varnish has somewhat dissolved the PLA material. As a result, an orange glow from the dissolved front is visible on the white background of the V electrode. I have no problem with that.

Well, hereafter are some more pictures of the finished inside of the ECG Patient simulator. I think it is a neat result and I'm very happy with it.
Everyone who has access to a 3D printer can download the .STL files under the download tab on this project and print this housing themselves.

Above all, let your own imagination run free and design your own housing. The satisfaction is so much better.

 

Have fun building this design.

 

Johan Smets
11/2020

 



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This ECG Patient Simulator project is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.