Protopasta Conducting Filament and the Photon

Not yet ready for full photon integration but Protopasta Conductive filament does work.

Needs a fine printing dual extruder 3D Printer. I have a fairly expensive Raise3d N2 printer, that can seperate objects 0.2 mm apart. My other 3D Printers are lucky to be able to separate objects that are 0.4 - 0.5 mm apart.

The yellow strip is regular insulating PLA the black is conducting. Squeeze the tips and current goes through. The resistance is about 2000 ohms. I can’t really print accurate enough to have insulating strips between each pin. On some random prints the black does kind of smear into the yellow causing a short.

So I outputted current through D4 and did a digitalRead at D6 an shoed the results at the terminal.

My code is here:

void setup() {
    pinMode(D6, INPUT_PULLDOWN);
    Particle.publish("Setup", "Done", 60, PRIVATE);

void loop() {
    digitalWrite(D4, HIGH);
    if (digitalRead(D6) == HIGH){  // the LED should go on if D6 gets power
        Particle.publish("Update", "D6 HIGH D7 On", 60, PRIVATE);
        digitalWrite(D7, HIGH);
    } else {
        Particle.publish("UPDATE", "D6 LOW D7 Off", 60, PRIVATE);
        digitalWrite(D7, LOW);

you should try a capacitive sensing example… a sphere that illuminates when touched. Protopasta interlaced over some compatible (which would they be?) alternate material.

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Really good idea @BulldogLowell. I see that all the capacitive touch sensors just need a voltage divider to conenct up to the Photon (Mess around with the large resistor size until your range of analogRead is sensibly between 0 and 4095 or close to it.).

I am putting my .STL 3D Printing files on my Photon Github site at:

Really nice on Github that you can easily view the .STL files. Reminder each print has an insulating and conducting part that are merged just before printing and are assigned to the left or right extruder, based on which one has the conducting and which one the regular PLA filament.

Here is todays’ images

The black PLA is electrically conductive 3D Printed filament and the yellow is regular insulating filament.

Not touching light off

Touching, light on

So lets try 2 capacitors. First a traditional parallel plate.

It worked but very low values even with larger resistors on the voltage divider. I maxed out at 100K ohm resistor so maybe it would work if I got into the M ohms.

Next a forked capacitive touch sensor design I saw on Thingiverse but I could not re-find it so I made my own.

This worked very well from a reading point of view. The voltage divider showed about ~1100 without touching the sensor and ~300 with touching the sensor. I did notice a bit of wobble with the numbers so I don’t think things are really stable, but it did work!:slight_smile:

All in all a good day. I did make a spherical capacitor but the insulator was too thin so it did not work.

I am working on a Cr2025 double battery holder and then will try to string several components together.

Today just made a single CR2025 battery holder and a double battery holder. Here is the double which can very dimly light an LED.

Was actually really hard to make since the battery must be snug or the connection will not be good. Did a few prints without the conducting filament until it was just perfect.

@peekay123 or @ScruffR or anyone?

Why can a voltage divider connected to A0 read good results from both variable resistors (as in the below diagram with a photoresistor) or a variable capacitor (like the above posts, touch sensors).

It seems to get good stable results from both.

Is it just that variable resistors and variable capacitors are both messing with the circuits total voltage causing the stable readings? Should I be using a different circuit for touch sensors that is better suited for capacitors?

Huh? :confused:
You are questioning why you get good, stable results?

That usually is what people are after, or not?

It is a deeper understanding WHY questions. Why do both a resistor and a capcitor do the same thing in the simple voltage divider circuit. I kind of know the answer just wondering if anyone can really explain it

I see.
But actually they don’t behave the same, so you might need to clarify what exactly you mean.
I guess we don’t need to discuss the actual voltage divider (two resistors) as this is straight forward.

But what exactly do you mean with “a volatage divider […] from […] a variable capacitor”?
I’d not call this a voltage divider.
How would your circuit look? Would you just replace the photo resistor with the cap?
Also what stable results do you get vs. what would you expect?

Maybe understanding how the ADC on these chips works also provides some clues to interpret the results you see