Nov 27

MSL & Curiosity

NASA’s Mars Science Laboratory launched yesterday on its 9 month journey to Mars. Now that NASA has retired the Space Shuttle and ended our manned space missions for the time being the future of space exploration is going to be a partnership between robots and humans. The latest version of this partnership is the Curiosity rover. Curiosity is impressive on virtually every level.

First of all, the sheer size of this rover is impressive. It’s the size of a small SUV at 10 feet long, 9 feet wide and 7 feet high. It has 20 inch diameter wheels a 7 foot long arm and it weighs in at just about 2000 pounds.

The Curiosity rover is also referred to as a mobile laboratory. The MSL mission’s overall scientific goal is to explore the landing region and assess the area as a potential habitat for life, past or present. This objective will help to expand our knowledge of the history of Mars and even help determine the feasibility of future manned missions. To accomplish the mission Curiosity is outfitted with 10 scientific instruments that are the culmination of the best sensors developed from groups in the US, Spain, Finland, Russia, France, Canada, and Germany. It’s truly a worldwide effort to advance humanity’s knowledge of another planet.

Even the landing system is revolutionary. For the Spirit and Opportunity rovers NASA used an airbag method to land the rovers. This method was successful, however, the first generation of rovers weighed less than 400 pounds, Curiosity weighs 5 times more. This approach to a landing puts a lot of strain on the rover in the landing process; the sensitive instruments on Curiosity may be damaged if landed the same way. In addition to these concerns, the other limitation is that NASA can only predict the landing site within a 50 mile radius. The solution to these concerns is a new guided entry system with a sky crane.

The rover, inside its heat shield, will enter the atmosphere at 13,200 mph, during decent the speed is reduced to 900 mph before a parachute is deployed at an altitude of 7 miles and slows decent to 80 mph. At about 1 mile off the ground the Mars landing engines activate and slow the decent to 1.7miles per hour. At an about 66 feet off the ground, the sky crane begins to lower Curiosity to the ground. Once Curiosity detects a safe landing, the tethers disconnect and the sky crane flies off to land a safe 500 feet from the rover. This is the first time NASA has tested this landing system. It’ll be an exciting day to watch the decent in action.

The Mars Science Laboratory mission is the latest and greatest project in the robotics field. I’m eagerly looking forward to August 2012 when Curiosity is expected to arrive at Mars.


Further Reading:

Scientific goals:


Nov 10

ElectroDroid App for Android

I’ve been using the ElectroDroid app for Android for a few months and I’ve found it to be a very useful tool to have in my toolbox. I initially found it while I was looking for an app that could help me sort through a pile of resistors that had become mixed together. The app makes it simple to calculate the resistance of each piece and it supports resistors with 3 to 6 bands. All you need to do is pick in the color of each band and the app gives you the resistance value.

ElectroDroid also has a variety of calculators that I use on a regular basis like a resistor calculator for LEDs that is similar and an Ohm’s Law calculator. Another very useful feature is the pin out reference info. They have pin out  diagrams for a large variety of connectors that you may need to use at some point including USB connections, serial, VGA, headphone jacks and ATX power supplies.

Overall ElectroDroid is a must have. If you find the app particularly useful there is also a Donate Version without the ads and a few extra features.

Nov 01

Powering an Arduino

There are 3 ways to power an Arduino; through USB, the barrel jack, or directly into the VIN pin. Each option has pros and cons and the method used depends on the project the Arduino is a part of.

Powering an Arduino from a USB is the way used by most people. When an Arduino is connected to a computer to load code, it also provides power for testing. If a project involves interaction with the USB port, in order to send or receive serial data for example, the USB is an easy, no hassle method. However, if a project is mobile or not in close proximity to a computer, a different power option will need to be considered.

Barrel Jack
The Arduino Uno, Mega and Ethernet (as well as the many of the older boards) have a standard 2.1mm center positive barrel jack connector. This jack has a diode to protect the Arduino from reversed polarity. This allows the Arduino to be easily connected to an AC-to-DC adapter or a battery pack. The recommended input voltage for this jack is 7 to 12 volts.

Stationary projects that will be near a wall outlet can be powered with a 9v or 12v wall wart power supply rated at either 1amp or 500ma.

For a mobile project, batteries can also be plugged into the barrel jack. The most basic option is to create a 9v battery adapter. There is a simple tutorial on Arduino’s webpage. To power a project with standard 1.5 volt alkaline AA and AAA batteries requires at least a 6x battery holder. If using rechargeable batteries remember that they provide different voltages, NiMH for example is only 1.2 volts. If the power supplied to the Arduino drops below 7v the output of the 5v pin may not be a full 5 volts and the board may become unstable.

The VIN pin on Arduino boards can be used to tap into the power source plugged into the barrel jack. Some shields will use this as their power source. The VIN pin is after the polarity protection diode so keep in mind that the output will be about .6 to .7 volts less than the input voltage.

This pin can also be used as an input for power. The only difference between the barrel jack and the VIN pin is that the VIN pin is after the polarity protection diode. This means 2 things: first if the power is connected with polarity reversed it will destroy the Arduino and second the power used by the Arduino will be slightly less, leading to longer life if powered from a battery. Once again the type of project and components will determine if this is the best route.

These are the 3 most common ways to power up an Arduino, however keep in mind that not all Arduino boards are exactly alike. The more specialized boards like the Lilypad, Fio and Pro have different power requirements. The new Arduino Ethernet also has an optional Power over Ethernet (PoE) option. Just keep in mind the type of project you are working on and keep experimenting!