Copying objects for 3D printing without a 3D scanner

Over the holidays I broke the smoke alarm in my flat. Not the smoke alarm itself as such, but the mount that held it to the ceiling. Judging by the amount of various adhesives that were on the mount, it looks as though a previous occupant had actually broken the mount, but bodged together enough adhesive to hold it tenuously in place until they left.

It still works, thankfully, but it's just hanging from it's power lead.


First of all, take photos of the object against a plain background. Ideally pick a background which contrasts well against the object that you're trying to copy.

  

Editing the image in GIMP/Photoshop
Open the image in a photo editor, and crop any unnecessary bits out the picture.

Create a translucent layer above the current layer, so that you're working on the new layer, but can see through to the photo.
Use the paths tool to trace around the object as best you can, invert the selection and delete the contents. This should remove all the surrounding background bits.

Use the paths tool a few more times to create the cut-outs you require - for example in my case it's removing the centre piece and the screw holes.
Then make the working layer opaque, and fill the outline shape with a colour.

Save and export this image as a PNG.

OpenSCAD is meant to be able to import and extrude PNG files directly, but I've found it to be unreliable, so the below is a workaround that I've been using.

Converting to SVG using Inkscape
Open the edited image into a vector graphics editor, such as Inkscape.

Click on the image, right click and select "Trace Bitmap". Select "Edge Detection". If the image being used is simple enough, you can leave the default values, click OK, and then close the menu.

Drag the bitmap out the way (you can delete it now), and you should be left with an outline of the object. Fill the outline with a colour to make the object solid.

Save this SVG file.

Extruding the file in Blender
Open Blender.

Go to File, Import, Scalable Vector Graphics (SVG). Find the file and select it.
You may have to zoom quite far in to see the imported object.

Select the object and move it slightly,  you'll see a second outline object that gets left behind. Click on the outline object and delete it, you don't need it here, then replace the rest of the object.

Next we need to set the units of the object, so that we can scale it properly. Click the Scene properties tab on the right, and select Metric or Imperial from the units section.

Next, we scale the object.








Press N to bring up the information about the object, and get the dimensions.

Set the X and Y scale here, but for the Z axis we need to extrude the flat image into a 3D object.

To do this, go to the right hand side and select object data, geometry, extrude.

In the case of my project, I added a couple of extra objects to recreate the latches which were broken off the original mount.


Once this is done export to STL and you have a file ready to send to the 3D printer.

Left, the original broken mount, and right, the 3D printed replacement.

Car Smoke Machine Pt 3

This is the final part of an on-going series of posts about a project to build and install a smoke machine in my car... for science or something...

If you missed the first two parts, they can be found here

• Wiring an interface to an e-Cigarette
• Car Smoke Machine

So far we've got an e-Cigarette and an air pump wired together to produce a cloud of smoke. Now what we need is to find a way to control it and install it covertly in my car.

I don't want the trap to spring too early, I need to give them time to get comfortable in the car and get started, for it to be believable.

Also, the motor driver chip will need some logic control, so it makes sense to use a microcontroller to provide the logic and the timings.

As I mentioned in the previous post, left to it's own devices, the eCig's coil gets rather hot, so in order to counter that I wanted the microcontroller to only switch it on in 5 second bursts, then wait 5 seconds for it to cool down.

I used an ATTiny26, for no technical reason other than I have a lot of them spare.


Microcontroller code

 1 #define F_CPU 1000000UL
 2 
 3 #include <avr/io.h>
 4 #include <util/delay.h>
 5 
 6 #define CONTROL_PORT           PORTA
 7 #define output_low(port,pin)   port &= ~(1<<pin)
 8 #define output_high(port,pin)  port |= (1<<pin)
 9 #define delay(a)               _delay_ms(a)
10 #define smokeEnable            PA2
11 #define setInput(ddr,pin)      ddr &= ~(1 << pin)
12 #define isInputHigh(pinr,pin)  pinr & (1<<pin)
13 
14 int isRunning = 0;
15 int secCount = 0;
16 
17 int main(void) {
18     setup();
19     while (1) { loop(); }
20 }
21 
22 void setup() {
23     DDRA = 0xFF;  // all outputs
24     setInput(DDRB, PB6);
25 }
26 
27 void loop() {
28         if (isInputHigh(PINB, PA6)) {
29                 if (!isRunning) {
30                         delay(10000);
31                         output_high(CONTROL_PORT, smokeEnable);
32                         isRunning = 1;
33                 } else {
34                         secCount++;
35                         if (secCount > 5) {
36                                 output_low(CONTROL_PORT, smokeEnable);
37                                 delay(5000);
38                                 secCount = 0;
39                                 output_high(CONTROL_PORT, smokeEnable);
40                         }
41                 }
42         } else {
43                 output_low(CONTROL_PORT, smokeEnable);
44                 isRunning = 0;
45         }
46         delay(1000);
47 }
48 

The finished circuit

Click to enlarge

The Videos
I was hoping to use this to prank as many people as possible, and get some good video footage, but unfortunately only 2 of the videos were really usable. The first, is Craigs "We're all gonna die lads!" reaction, and the second, is Bethany's obliviousness to the cloud of smoke forming around her. Enjoy.

Car Smoke Machine

A prank that's been doing the rounds in my office is that if you leave your car keys unattended on your desk, you can expect that your car probably won't be where you left it when you leave for the evening.

I've been kicking around ideas on how to improve on this gag, and at the same time defend my car from it happening to me.

My idea was to orchestrate a scenario of deliberately leaving my key for someone to try and move my car, and setting up a surprise for them when they get in. If I could make the car appear to be breaking down, would they own up thinking they broke the car, or just put the key back and deny all
knowledge?

So, what do we need to make it seem a car's breaking down? Noise and smoke.

The noise is quite simple, take a vibration motor from an Xbox/Playstation controller, wire it up and put it in a small container of screws & random bits of metal, so when it vibrates, we get a metallic rattle.

The smoke, not so easy. All the consumer smoke machines I could find required mains power, and would be far too bulky to conceal in the car, so I have to roll my own.

Thankfully vaping and e-cigarettes have made battery powered, small, smoke producing devices quite cheap and readily available.


I purchased a few e-cigarette "Atomisers" from amazon and did some testing. See this post for a write up of how I wired up the eCigarette.


Unless there's a person 'drawing' on the device, the smoke cloud just sits there, so I'm going to need to create a pump or fan to force air through the atomiser.

A quick test with some old computer fans that I had lying around showed that they weren't powerful enough, so I found a battery operated air-mattress pump that would do the trick.


The pump appears quite bulky, but it runs on 4 D Cell batteries. As we're not going to need those, a large proportion can be cut away, streamlining the whole thing.


To drive the motor of the pump, I'm going to use the same SN754410 that I'm using to power the e-Cigarette (this is why I used the SN754410 in the previous post, as it's capable of driving two motors, or in this case, one motor and one e-Cigarette.)

This is how the original circuit was planned. The input voltage is 12v as this is the most readily available source in the car. (The EN pins and motor logic will all be connected to the microcontroller - left off in this diagram).

Testing this circuit turned out that 1 amp per 'motor' wasn't powerful enough to drive the pump, so I ended up putting the eCigarette coil and the pump motor in series, and joined the two motor channels of the SN754410 in parallel to double the available current. This isn't an ideal solution, as the resulting heat of the eCig coil is a bit excessive, but I only need it to work in short bursts, and I can control that from the micro.

The revised circuit

Here is the first working test of the smoke machine:

As the pump makes enough noise, I decided that the vibration motor was a bit unnecessary, so left that off the final design. Essentially the device is a simple micro-controlled smoke-machine.

Wiring an interface to an e-Cigarette

I'm currently working on a project that requires the use of an e-cigarette.
I'm not a smoker, so as far as that aspect is concerned, I might be a little off on the terminology, but eCigarettes, vapourisers, whatever you want to call them, essentially follow the same principle. There's a battery, a small reservoir of vaping fluid, a wick, and a wire coil.


Current is passed through a coil which causes it to heat up, in turn heating a wick soaked in fluid which turns it into a vapour.
We can ignore the battery component, it's only really the wire coil I need for the project. I do however need to control it, so I needed to find a way to interface it.



The coil connects to the battery by a screw-type connector which appears to be specifically for these devices. In addition, the connector also contains a small gap which acts as an air inlet for the user to take a drag on it.

This causes problems when trying to create a connection, as connectors run the risk of blocking the inlet.

Coincidentally I found that a male TV aerial connector is an ideal size to create a push-fit connector. The next task is to decide how to control the current flow. Simply switching it on and leaving it will cause it to overheat.


Coils like this can be controlled in similar way to motors. In fact, the IC I'm going to use to control this is really designed for driving motors, but works fine for the purpose of this.

The chip is the SN754410 H-Bridge motor driver - which is completely overkill for this, but as this is forming a part of a larger project, the reasoning will become clearer later.

The pinout for the chip is available on the third page of this datasheet. Treat the vapouriser as if it was a motor - polarity/direction of travel doesn't matter.

For the motor drivers voltage I'm using 12v, which, again, is overkill for this part in particular, but the coils are very tolerant of it, and use the speed control function of the chip to control how hot the coil gets.

That's all for now, stay tuned for the 2nd part of this project...