It’s the classic new media problem: you’ve got a cool show abroad, but will all your technology still work over there? I need to determine whether this board and this SIM card will be compatible in Hong Kong. This page suggests that 2G (a limit presented by the board) is still available in Hong Kong, and that the 900 band is still active. I suppose my fallback will be purchasing SIM cards when I arrive, but I’d like to avoid that. It may be cheaper, however, so maybe I’ll try both.
A little research online seems to indicate the potential for IR LEDs to damage eyesight. Perhaps this is the tinfoil hat squad talking, but I don’t want to take chances with my kid’s eyesight. Thus, we need to wire/program the pi so that it only flips the IR array on during active recording.
A little poking around revealed that the status of the camera (“ready” or “halted”) is held at /var/www/status_mjpeg.txt . I created a simple python script in the same directory called checkCam.py:
# status can be "ready" or "halted"
import RPi.GPIO as GPIO ## Import GPIO library
GPIO.setwarnings(False) ## Prevent constant warnings (maybe I did something inelegant?)
GPIO.setmode(GPIO.BCM) ## Use board pin numbering
GPIO.setup(7, GPIO.OUT) ## Setup GPIO Pin 7 to OUT
if 'ready' in open('/var/www/status_mjpeg.txt').read():
GPIO.output(7,True) ## Turn on GPIO pin 7
GPIO.output(7,False) ## Turn off GPIO pin 7
Lastly, edit /etc/rc.local with nano to include python /var/www/checkCam.py somewhere before exit 0 . That will cause the script to run on startup.
Next up: connect pin 7 to a transistor so that it can control an IR array!
Somehow I’ve managed to make it ~15 years without really understanding the multiple lead ports found on a standard multimeter. At a bare minimum you’ll see COM, V/Ω, and A. COM is the easy one, as this is always attached to the black lead. I’ve always used my meter to sense voltage and/or resistance, so I’ve never connected the red lead to A.
I learned my lesson today when I grabbed a random meter from the lab at school. Someone had been noodling with the lead attachment, so COM and A were connected. When I tried to test AC voltage coming out of the wall, I got a big spark and fried the extension cord I was testing. This happened even though I had the dial set to the correct AC range.
So what happened? I found it difficult to track down the answer online, but I finally came up with this page. Near the bottom you’ll see an image that describes what I did:
Sensing current (A) requires that the meter provide no or very low resistance. Makes sense – if the meter introduced resistance, you wouldn’t get an accurate current reading. This feature can also be dangerous; turn the dial back to V/Ω, but forget to use the correct lead ports, and you’ll short the circuit through the meter. Many meters have safety features to help remind you not to do this, but cheap meters lack these fail safes. Fair warning!
Just pushed some big updates to Github, where I’m tracking the process of getting a Chinese 6040 mill up and running. Check it out and participate if you’re interested.
Got a chance to hang out with the excellent Dave Jones on Saturday night at his studio. He’s been working with video artists since the 70’s, designing and fabricating electronics for live video signal manipulation. There was so much good stuff to see, including this old school schematic that was done by hand with tape.
The kitchen sink at Signal Culture was missing a faucet handle so I made them a new one. I love sneaking plain, functional objects into public environments where they become useful and invisible. Unlike more precious art objects, these items are designed to be handled and forgotten (even as they give me a semi-permanent presence in a space).
One of the great things about the Signal Culture residency is that they understand tool making as a creative practice. I brought along my 6040, an aluminum mill that I bought from China via eBay. Though I did not fabricate this mill myself (like we did with DIYLILCNC), the 6040 came with no instructions, so I’m applying all my DIY know-how to getting it up and running. I’ll use both this blog and github to document the process.
The good folks at Element14 got in touch after they read some of the Raspberry Pi tutorials on this website. They offered to send me some parts for a project, so I decided to start with a networked baby monitor. I’ll post progress as I go!