TD Moose

Old RC toy made into a garage alarm

My wife wants some sort of indicator to show when the garage door is open. The garage is visible through the back window, but sight lines make it difficult to determine. Also, when the shades are drawn, there is no visiblity. I considered X10 modules at first, but that just seemed like overkill when all I really wanted was a small led to illuminate.

Then, I remembered an old RC toy car my son had. The controller unit was simple, with just one button. Pushing the button made the car go forward. Releasing it made it go backwards while turning. On the receiver (car) side, the controller signal caused a voltage to toggle between -1.5 volts and +1.5 volts. With a little testing, I found a point that toggled between 0 and +3 Volts. This was just enough to provide drive an LED. A magnetic reed switch from Axman Surplus worked perfectly for the door sensor. This switch is in the off mode when the magnet and reed unit are near each other (door closed). When the door opens, the magnet will be pulled away and complete the circuit. The transmitter and switch are hooked up to a PIC16F684 chip. The reed switch is connected to pin 4, which is configured as a digital input. When the reed switch is open (door closed), the signal on pin 2 goes high. This turns on an NPN2222 transistor, which in turn causes the transmitter to send a signal. The receiving unit goes to +3 volts on the output when there is no signal, and drops to 0 volts when there is a signal. In other words, when the door is down, the LED indicator is off. This may seem overly complicated, but it has one advantage. If the garage-side (transmitting) unit fails, the light will come on. Although this may be a false positive for the door being up, it indicates that something is wrong on the transmitting side (power failure, loose wire?).

Circuitry from RC car repurposed as a garage door alarm

Side glow cable with LEDs

Many projects require illumination.  An LED is often a good choice because it can be bright while using a minimum of current.  An ultra bright LED can even drive enough light through short lengths of side glow fiber optic cable.  This cable is flexible plastic cable with a reflective core to direct light to the side, as opposed to simply transmitting the light to the end of the cable.  While it is designed to be used with bright halogen bulbs that push light through hundreds of feet of cable, I was interested to see how well an LED could work with just a few feet of cable.

My wife and I are interested in making safety clothing for night bicycle riding and thought this might be useful. We ordered a five foot section of 3mm wide cable from here. Once I had the cable in hand, I attached a bright red LED to each end with shrink tubing.

End connections

A quick test shows that two LEDs provides a fairly even glow along the entire length of the tube. Each LED was rated to deliver 18,000 millicandelas of light.

Two LEDs powered up

This looks like it could be used on a bicycle helmet to provide a flashing illumination. More to come as we experiment.

Improving a book light

I love to read.  Often, I use a portable light that clips onto the book.  It works OK, but two things bugged me about it.  First, it required four AA batteries.  Second, it used an incandescent bulb that is bright, but which produced glare and hot spots on the page.

Original bottom view

I had been experimenting with a simple circuit called a Joule Thief.  This circuit boosts a DC voltage to a higher voltage.  It’s is easy to make with easy to obtain parts.  The Web is full of plans for these devices.  The advantage for this project, is that such a circuit can drive a bright white LED from a single 1.5 Volt battery.  I figured that I could easily fit the circuitry and a single AAA battery into the battery compartment of the book light.  This would save batteries and provide a more even light across the page of a book.

Joule Thief

I replaced the incandescent bulb with a bright white LED that I encased in aquarium sealant inside of a short length of clear plastic tubing.  This helped to diffuse the light along the approximately two inches of tubing that the LED was attached to.  Here’s the final assembly and it’s use.

Ready to use

Modified lamp in use

Vex Servo Motor

Vex servo motors have a lot of good features. They are compact, powerful, and easy to mount and connect to things like gear shafts, beams, levers. I’ve been using micro controllers to operate these in previous projects, but decided to go old school and use a 555 timer. I really just want to do something to try out my new USB oscilloscope. I found this page with a couple of good plans.

wolfstone.halloweenhost.com

Breadboarding this was fairly easy and took just a few minutes.  I keep a lot of components around with breadboard wire already soldered, so that makes prototyping a lot faster.

Before I attached the motor, I verified that the circuit was performing as needed.  With the oscilloscope set to show 5 ms per division I could measure the minimum pulse width of 1.15 ms and a maximum width of 2.75 ms.

This seemed good enough to try, so I plugged in the motor.  The black wire is ground, the red (or orange) wire is positive, and the white wire is the signal (pin 3 on the 555).    I had nearly the full 100 degree rotation in the motor as I turned to potentiometer shaft back and forth from minimum to maximum.

Just for fun, I substituted a flex sensor for the potentiometer.  Not quite the same amount of rotation, but, I didn’t bother changing any other component values.

Servo Motor with Flex Sensor from Patrick Lewis on Vimeo.

Bill Gates at the Computer Bowl

My favorite Bill Gates moment ever. This comes from a show called the Computer Chronicles that aired sometime in 1993.

The man answering the question is Jean-Louis Gassee, one-time Apple executive, probably best known for BeOS.

The correct answer, BTW, was “The Obfuscated C Contest.”

Taking apart a Flip Ultra 30

The Flip camera is great and cheap enough to risk destroying it.  Broken down to its bare bones, it is still a little bigger than its predecessor, the  Pure Digital One-use camera. However, the built in USB port and connector, and the ability to connect the Flip to a PC without needing the hack it to access stored videos, makes it more useful in the long run.  In short, a great camera for projects that need small, light, durable video recording hardware.

MySQL firewall issues on Fedora

This is my experience with making a MySQL database on one server accessible to a mysql client on another server. While this issue has been addressed extensively, I think the solution to my problem was something that was not mentioned in any of the sources I searched.

Accessing the DB server worked on the local machine, but, this was the message I received when attempting to access the it on a remote host.

“ERROR 2003 (HY000): Can’t connect to MySQL server on. . .”

I eliminated some other things as potential causes right away. My permissions for the user and host were set properly. The MySQL server was not started with the “skip-networking” option set, and the server was not restricting TCP access to localhost.

Narrowing this down to a firewall issue was pretty straightforward. First, I stopped the firewall.

/sbin/service iptables stop

Then I tried again to access the DB server remotely and succeeded. When I restarted the firewall, the problem returned.

Searching on the net, I came across this recommendation in many places. Basically, a command to add an entry to open port 3306.

iptables -A INPUT -i eth0 -p tcp -m tcp –dport 3306 -j ACCEPT

I entered this but it still didn’t help. Then, I began to look at the iptables configuration with this command.

ipatables-save

This just writes the iptables entries to STDOUT. What I noticed was that the entry for port 3306 was preceded another line. Here is how the two lines appeared.

-A INPUT -j REJECT –reject-with icmp-host-prohibited
-A INPUT -i eth0 -p tcp -m tcp –dport 3306 -j ACCEPT

I sent the result of the ‘iptables-save’ to a file and then edited this file and switched the order of the two lines above. Then I restarted the firewall.

/sbin/services iptables restart

This worked and my databases have been accessible since.

Go bananas for bananas4apples!

Help out a friend of mine to get his blog off the ground.

In his words, “It’s a place to learn cool stuff about your Apple computer and Leopard.”

Check out the site at bananas4apples.

Extinguishing a kitchen fire

Bottom line is not to throw water onto this type of fire.

Re-inventing the scale.

Must have been a long winter stuck inside to try something like this. The idea was to make a scale using a couple of pennies and conductive foam used for packing electronic parts. The first thing was to solder some wire onto pennies. I used a torch instead of a soldering iron because pennies can soak up a lot of heat.

Pennies with hookup wire soldered to them. Foam is packing from a power MOSFET.

The next step was cut some plexiglass sheets and then use some double stick tape to attach a penny to each sheet. Then I bolted the two sheets together, presssing the foam in between. Here’s the assembled unit.

Platform assembled, and hooked up to ohmmeter to test base resistance.

This setup didn’t work out so well as a scale. Heavier objects placed on the scale took a long time to reach a stable value. I figure that the foam continued to compress slightly for two minutes or more. Also, it took a similar amout of time for the scale to return to it’s base value.

This arrangement seems to work best not as a scale, but as a pressure pad, particularly as a pressure-relief pad. For example, it might work well to sense when an object, such as a book, is lifted. Don’t anyone dare try to steal my “Programming Python book!”