Sami Yanikoglu
Our HAB will have two mounted cameras on it. The primary camera is a GoPro Hero camera pointing 30 degrees so that we record the ground and curvature of the earth at maximum altitude. Our secondary camera will be mounted on the sidewall of our payload; the Vivitar iTwist camera will be wired to take a picture every minute for the duration of our flight. In order to capture images over this interval external leads were connected to the capture button of the camera, as well as an opto-coupler in order to connect/disconnect the button. The 4N25 opto-coupler is an alternative relay that uses a phototransistor and LED to regulate power to a device. Our Arduino is programmed to flip the opto-coupler switch on to take a picture. Prior to launching our balloon we will freeze our cameras in order to prevent lens frost.
Nichrome wire was hooked up to an opto-isolator. The opto-isolator is connected to and XBee RF receiver that will receive a signal from our main arduino board when the 3 hour ascent time has eclipsed. The opto-isolator will then connect a 9V battery source to 6 inches of NiCr wire. 32-gauge wire is 10 ohms/ft so we will have a 3 ohm resistance for the wire. With a 1A current the wire will heat up to 700 degrees Celsius for 10 seconds to cut our payload from our balloon.
Update:
We were not able to use the opto-isolator as a relay with the NiCr wire. The 5V, 70mA signal from the arduino did not supply enough power to heat up the wire. We then tried using a traditional electromagnetic relay (EC2-5NJ NEC) to switch the cut-down circuit on. When we tested the cut-down circuit we found out that a brand new 9V battery is needed supply a high enough voltage to heat up the nichrome wire. With slightly used batteries we were able to cut through the cord in about a minute, while we cut through the cord with a fresh 9V battery in 15 seconds.
No comments:
Post a Comment