Category Archives: 3-D Printing

Why is choosing a 3-D printer so difficult?

Upgrade path?

Today, there are hundreds — if not thousands — of 3-D printers for sale. You can pick up cheap ones for under $100, or get a well reviewed “good” printer in the $200-$300 range.

But which one should you choose? Every “good” printer, if you read the reviews, has tons of folks praising it as their favorite, and tons of folks saying it’s garbage and is nothing but problems. The 3-D printer market seems to have very inconsistent quality control.

But beyond that … here is what we need:

Buying a 3-D printer: What we need.

Part 1 – An elimination system.

When I ask about a printer, folks always say “it depends on what you want to do with it.” The first round is to simply eliminate printers that do not meet your requirements:

If you have specific needs, such as how large an item you want to build, or how fast you require it to be built, you can immediately stop looking at all printers that do not meet those requirements. You can do the same with OS support (Mac, Windows, Linux).
Not all printers print all materials. If you want to print flexible materials, some printers are great at that, and others cannot do it at all. If your goal is to print “rubberized” phone cases, you can instantly eliminate alot of choices.

Part 2 – Quality

The next part is something that should be 100% achievable without any opinions getting in the way. The job of a 3-D printer is to take a digital design and turn it in to the three-dimensional object. It should be trivial to simply run through a series of prints that exercise different aspects of printing (overhands, the need for supports, etc.) and then scan the resulting object and compare it against the digital blueprints. You should be able to end up with a simple list of accuracy in different categories, much like any auto buyer’s guide breaks down vehicles in to a simple set of basic categories.

Part 3 – Opinion

The last part should be the opinion part. How many units were dead on arrival? How many have had to be repaired? How fast is support? etc.

Even if you find the best printer, if it breaks and you can’t fix it, maybe it’s not a good choice. BUT, maybe you are fine getting past a project even if your printer breaks in six months and never runs again. That is why I think this choice should be last.

So … why is there no such website? Number two should be especially easy, as would be speed. At least we should have those.

Until next time…

PiZ SuperCap safe shutdown for Raspberry Pi Zero

How it works

Here are some things to be aware of:

When you first apply power, the Pi Zero will not immediately power up like you are used to. It must first charge the capacitor. The Pi Zero won’t actually start up until about 8 seconds after you apply power.
When you turn off power, if no shutdown script is installed, the Pi won’t turn off until the capacity runs out. On my Pi Zero W (first version), I timed it at 75 seconds when just sitting at a text console login prompt. If you are running a graphical desktop or any programs using the CPU, it won’t last that long.
The PiZ SuperCap will toggle GPIO pin 4 to indicate a power loss. To enable safe shutdown, you need some form of program or script that will monitor GPIO pin 4 and shut the system down when power goes away. The sample code provided uses a 9 second delay before deciding to power off, making the unit act like a mini UPS rather than shutting down on any temporary power blip. Clever.

Shutdown script

The designer provides some sample Python code on the project page, but here is a shorter one I came up with. I am not a Python programmer, so I have no idea if my technique is good. I just wanted it to block until it sees a power loss, and either shut down (after a delay) or continue:

supercap_shutdown.py

#!/usr/bin/python3

import RPi.GPIO as GPIO
import time
import os

GPIO.setmode(GPIO.BCM)
GPIO.setup(4, GPIO.IN)

while True:
        # Wait for power to drop.
        print ("Waiting for power loss...");
        GPIO.wait_for_edge(4, GPIO.FALLING)
        print ("Power loss")

        # Give user 9 seconds to restore power.
        print ("Waiting to see if power is restored...")
        time.sleep(9)

        if GPIO.input(4) == 0:
                print ("Power not restored.")
                os.system("sudo shutdown -h now")
                break;
        else:
                print ("Power restored.")

The above script has print statements in it so you can run it from the console to verify it is working. Those can be removed (or commented out) once you are sure it works.

You will need to do a “chmod +x supercap_shutdown.py” to make it executable.

If you want to make it run on startup, edit the /etc/rc.local file:

sudo pico /etc/rc.local

…and add this line at the end before “exit 0”:

# Pi Z SuperCap monitor script:
python /home/pi/supercap shutdown.py

You can then restart the system (“sudo restart now”) and when it reboots, the script should be running. Disconnect power and after 9 seconds (or whatever time you modify the script to use) it will issue a safe “shutdown” command.

3-D printed enclosure

I have created a very simple 3-D printer enclosure that holds a Raspberry Pi Zero and the PiZ SuperCap. Let me know if this is something you might want.