RFID Acces Control - UPS Prototype

This week, we made more progress on the Open Source RFID Access Control project. The 5A power supply with UPS and battery charger has been prototyped (using another toner-transfer resist board) and is undergoing testing.

Check out:

And the board:


Balloon Launch Video

Here is a video of the balloon launch:

20gm payload balloon launch

High Altitude Balloon project

So we've started a new project at the shop: a high altitude balloon. This started when we acquired an 80ft^3 Helium tank when we bought out at an estate full of old tools and supplies. The eventual goal would be to be able to send a package of instruments and a camera up to 100,000' and recover it at will. Rather than risk $100s in electronics right off the bat, we've decided to use a "progressive" approach to gain experience and test systems. Here is what we've done so far:

1. The $1 flight: We bought some 17" "jumbo" party balloons from the balloon wholesaler down the street. (Funtastic on Lemon/Raymond). Some testing shows that this balloon will burst at 24-25" and has a gross lift of just over 35gm. Based on this, we flew one with 22.5gm of payload (sand) and got around 150m/min in climb (estimated). Using the balloon burst calculator, we estimate that this balloon could go to 20-25K feet.

Status: Successful

2. The $10 flight: We launched the same balloon, but added the following:

  • A parachute of 20cm, made from a black trash bag, some 6lb test fishing line and a bit of Scotch tape and a fishing swivel.
  • A small radio beacon, made from leftover parts. Used a 23A battery and a 6" piece of 30ga wire for the antenna. We had trouble getting it to oscillate with a bigger antenna attached, probably due to capacitance issues.
  • 3m of 10lb test fishing line to hold it all together.
  • A 10K thermistor from Sparkfun.com, to change the beacon's tone in response to temperature.
This package got flown last weekend in the Mojave desert. What we learned:

1. This balloon/weight combination has plenty of lift to send the package much farther away than you can see even with binoculars.
2. The tiny radio transmitter, with its inefficient antenna and <20mw output could not be tracked after about 30seconds, even with a good directional antenna and receiver.
3. The white styrofoam package with clear tape and the black 'chute were very visible, even at several miles.
4. Testing the parachute from the roof of the shop shows that it deploys 100% of the time. 60gm of weight could be brought down nicely with a 30cm chute.

We did not get this package back, due to the wind picking up and sending it over a mountain.

Status: Partially successful



Laser Printed Masks for 2-Sided Circuit Boards

Printing on glossy inkjet paper -- 20 cents per sheet -- and ironing the paper onto a clean PB gives an almost perfect transfer of the mirror image as an insulative mask against ferric chloride etching. (I have read that magazine paper also works -- experiment with any claycoated paper or cover stock.

Don't use steel wool to scrub your board, it leaves little scraps that can interfere with etching as they rust. Scotchbrite seems a good solution instead, being nonmetallic. You're scrubbing to degrease so a shot of vinegar or alcohol would help. Wear gloves. Scrub everything bright.

Arclight suggests setting the iron to NUCLEAR for the ironing step. Line up your paper (extra registration steps required for 2-sided boards) and tape it on, then fold back the paper. Preheat the board 30 sec with the iron, flap the paper back, and iron firmly.

Let cool, then soak in water to remove the paper. Pull or roll it off gently at first to make sure it's transferred, which it should be, and rub with a finger to get any excess pulp off. (It shouldn't be too delicate after cooling.)

After mask application, go over it with a nice fresh Sharpie or other resist pen or tool to perform any mask touchup or fix any dropout spots.

Soak the board upside-down a few minutes in warm ferric chloride etching solution. Do this on paper, in the dirty side of the shop, with nitrile gloves and a nonmetallic tray and tools. FC eats all kinds of metals, including your aluminum camera and laptop, it stains absolutely everything -- skin, cloth, tile, cement, metal, etc -- and it is a real stinking mess if you spill it.

Remove the board and neutralize any excess FC with baking soda, then rinse in cold water. Baking soda is a shop staple for many reasons as well as neutralizing acids and removing funky odors from the shop fridge.

That's all that's required to make totally serviceable 2-sided boards.


Reverse Geocache

A while back, a friend of ours asked if we could build one these for him:

Reverse Geocache Puzzle Box

Since I like a challenge, I went for it. I ended up using the EM-406A GPS module from U.S. Globalsat, a standard Arduino 328 board, a backlit 16x2 character display from Futurlec.com, and the Pololu soft power switch from Sparkfun.com. The code will be cleaned up and posted soon.

Here are some pics of the build and completed project:

Initial board:

Open Access Control - Power Board with UPS

Thanks to Martin Wood from the hackerspaces.org mailing list, we have a v1.0 circuit for the UPS/Power supply board. I decided to break this out into a separate board so that it is optional. The basic circuit floats a 12V sealed lead acid battery at around 13.5V, and uses this as the regulated output for sensors and door locks.

Also, it looks like MOVs (metal oxide varistors) are the way to go for clamping the voltage spikes from a door-holding magnet.


Shop Party 4/17 - 4/18

With no layerone this year and a powerful urge for some defcon warmup, we're
going to throw a giant birthday party for Amber who recently moved out of Utah! It's at the 23b shop, there will be TWO POOLS and a CAKE FIGHT.

Bring: girls, booze, fun, swimsuit, stuff to work on at the shop

Invite: Everyone

Pump up: the volume

Sat April 17th, any time (people should be there friday 8pm to sunday 6pm)
no drunk driving! Everyone is welcome to sleep at the shop, bring a pillow/blanket though.

418 E Commonwealth Ave
Fullerton, CA 92832



Open Access Control - Code

The code and v1.0 Eagle file has been posted to Google Code. Check out:


Open Access Control v1.0

The hardware design for the Open Access Control for Hacker Spaces is nearly done.
This system uses the Arduino Duemilanova board with Atmega 328, and provides:

-Shield compatible with Arduino
-DS1307 Real-time clock with battery backup
-(2) Wiegand26 reader inputs (optoisolated)
-(4) Alarm zone monitor ports using Analog0..3 (optoisolated)
-(4) Relay outputs, rated to 10A/220VAC
-Spare pins 10..13 to enable Ethernet shield use
-Built in 12V unregulated, 5V regulated, 12V regulated supplies for alarm sensors, door hardware
-Built in UPS (smart charger in next design)
-Separate fuse protection for everything

Check out: