so it was time to tackle the headach... having 3d modelled my brain, and added a mechanism in the bottom to screw and unscrew a lid to put things into its inside, i decided to offset the surface mesh of my brain by 1.2mm. this dimension was determined by the printer and nozzle i intended to use. because of its size, i was not able to print my brain on a prusa mini, but rather used a prusa i3 mk3s with a 0.6mm nozzle. since the printers would have a hard time making a shell out of a single layer of pla, i decided to go with 2x 0.6mm = 1.2mm thickness. since the printer buildsthe object up layer by layer, the thinnest parts would only be a few, as soon as the geometry is not perfectly vertical (which it is almostnever) it will automatically have to put more than one layer of pla down before moving on.
to double check that my math was correctly executed, i used prusa's slic3r software. i went into the horizontal slices and went through the simulation of a critical layer to see whether it would be able to build a new layer of filament ontop of the previous one.

while at this point i trusted the process enough to think that 1.2mm was thick enough, i did not want to test my luck by printing the brain completely without supports (it might have worked because of the geometry). the original printing time was around 30h and it would have printed supports in the inside of the brain, so i decided to print the two sides of the brain into separate print jobs, cutting the printing time per half to roughly 12h each. fortunately, i was able to run two of the same printers simultaneously and was able to stay true to the 12h mark. i started printing one half and let the job run for about an hour before starting the second one. i wanted to make sure that the print and shell would work well before i risked two prints running into issues.

at this point it's worth mentioning, ask your shop managers/monitors/specialists what filament you are allowed to use on which printers! not every filament contains the same components to achieve the effect they are supposed to have. glow-in-the-dark filament, despite being PLA can be really abrasive and hard on the printer nozzles, especially if they are brass ones (which they normally are). if you use a filament like this uv-reactive one, it is hard to find info about its effects on the nozzle... therefore, definitely ask your shop what you are allowed to use before you spend money on it. the shop in N51 has two printers that they reserve for more experimental filaments (so that other printers always work for other students)

while most normal supports look different, i thought that organiz supports would fit the theme of a brain much better. they look like little trees or a diagram of nerves.

12 hours later it seems to have printed the last few layers almost completely horizontally, solely relying on the support trees it has been building up. this is a scary part. the resolution of the printer in the z-direction is lower than it has in the x and y; adding a new layer is bound to the thickness of the layers, which for a print like that, i had to pump up a little, otherwise it would have taken forever.

once i remove the print, i let it cool for a bit. i want it to come off the building plate in one piece. i recommend bending the sheet slightly. one can tell when the print pops lose from the building plate.

at this point i wished i didnt have already a plan of what to do with the insight of the brain... unfortunately these tree structures have to go... -.-

most of the supports came out super easy, however, as i mentioned above, the last layers are not very stable. pulling on the supports too hard, since they are just holding horizontally printed layers, would risk peeling them off (the print is much stronger in x and y than in z direction).

once i have them removed, it is time to try the lid that i printed on a prusa mini in the meantime. once i made sure it would be able to insert and snap shut, it was time to test the other parts.

as i mentioned in the beginning, this PLA was supposed to be UV reactive (here ist the PLA i got from microcenter for this print - Inland 1.75mm PLA UV Color Change 3D Printer Filament 1.0 kg (2.2 lbs.)) it was already dark out when i got to this point, and i did not have any uv light source available but a few lose uv leds NTE Electronics UV Purple Discrete 3mm LED Indicators - 10 Pack that i got also at microcenter. so i decided to hook them up to an arduino uno and a bread board to see what the PLA would do.

while the uv leds are one, they are visible as violet/blue shine through the print. i set them up to light up for 10 seconds in arduino.

as soon as they turn off, the PLA remains red for a few minutes before changing the color back to white! pretty fun

once i had it all figured out, i just soldered all the wires together, added a button that was originially mounted on the brain (would fall off later), and soldered a power plug that would act as external power supply (9-12v) for the receipt printer.
to run the thermal printer on the arduino uno i needed to install and include the "Adafruit_Thermal.h" and "SoftwareSerial.h" library.

here is a test example code:
#include "Adafruit_Thermal.h" #include "SoftwareSerial.h" #define TX_PIN 6 #define RX_PIN 5 SoftwareSerial mySerial(RX_PIN, TX_PIN); Adafruit_Thermal printer(&mySerial); const int btnPin = A0; int btnVal = 0; void setup() { pinMode(btnPin,INPUT_PULLUP); pinMode(7, OUTPUT); digitalWrite(7, LOW); mySerial.begin(9600); printer.begin(); } void loop() { btnVal=analogRead(btnPin); if(btnVal<200){ // We press the push button printer.println(F("Arduino")); } }

for the final result i hoped to have the arduino pick random dictionary entries and prints them out including the definitions, but the internal memory of the arduino uno's are not big enough so i included merely a few words... but that worked. I hope i get to make my own pcb with a memory card and or wifi connectivity to parse the information from the internet, or get a voice to text interpreter, that could run a ChatGPT token to have a physical chat interface.

for now, i'm happy i made it work that far. here is the code i used:
#include "Adafruit_Thermal.h" #include "SoftwareSerial.h" #define TX_PIN 6 #define RX_PIN 5 SoftwareSerial mySerial(RX_PIN, TX_PIN); Adafruit_Thermal printer(&mySerial); const int btnPin = A0; const int ledPin = 7; int btnVal = 0; unsigned long previousMillis = 0; const long ledDuration = 10000; // LED duration in milliseconds (10 seconds) bool printed = false; // flag variable to track printing status // collection of strings const char* phrases[] = { "long-term", "gruesome", "like", "gabby", "separate", "average", "deeply", "moldy", "addicted", "taboo", "handsome", "confused", "languid", "exultant", "majestic", "spicy", "various", "disastrous", "cloudy", "knowledgeable", "necessary", "worthless", "breakable", "tough", "limping", }; void setup() { pinMode(btnPin, INPUT_PULLUP); pinMode(ledPin, OUTPUT); // set the LED pin as an output digitalWrite(ledPin, LOW); // LED is initially off mySerial.begin(9600); printer.begin(); printer.setSize('L'); } void loop() { btnVal = analogRead(btnPin); if (btnVal < 200 && !printed) { // button pressed and not printed yet digitalWrite(ledPin, HIGH); // turn on LED printed = true; // set the flag to indicate that printing happens previousMillis = millis(); // save current time // pick a random index int randomIndex = random(0, sizeof(phrases) / sizeof(phrases[0])); // printing printer.println(phrases[randomIndex]); printer.println("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"); } // check if the LED time is over, then reset if (printed && millis() - previousMillis >= ledDuration) { printed = false; digitalWrite(ledPin, LOW); // turn off LED } }

because the images i used to model my brain are actual medical records, i do not want to share the 3d model of it, sorry for that.