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group3:group3weekly 2008/10/22 22:01 group3:group3weekly 2008/11/24 11:34 current
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-== Week 7: October 13-18 ==+== Week 7: October 13-17 ==
The group discovered that the microcontroller we ordered is a surface mount!  This means it has no leads and cannot be easily mounted on a circuit board.  A new PIC microcontroller has been ordered from Microchip as a free sample, paying attention to packaging and making sure it is compatible with our programming software. The group discovered that the microcontroller we ordered is a surface mount!  This means it has no leads and cannot be easily mounted on a circuit board.  A new PIC microcontroller has been ordered from Microchip as a free sample, paying attention to packaging and making sure it is compatible with our programming software.
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 +
 +== Week 9: October 27-31 ==
 +
 +At the start of this week, the group met to work on the electronic proof of principle test. A productive experiment was completed in which a comparator circuit was designed which can work directly with the output signal of the phototransistor to create a digital output. The waveform produced was suitable to be read by an RS 232 connector. There was noise however near the flip flops which was the result of the lack of a schmit trigger to prevent noise from giving the comparaor a mixed imput.
 +
 +Later in the week, the group completed the proof of principle sucessuflly. The laser driver circuit was a simple n channel mosfet which takes in a signal from an RS232 or function generator to drive the transistor to allow a seperate power supply to power the laser diode. The reciever circuit is a comparator with a schmit trigger to eliminate noise while not in operation. The circuit operates at 115kilobaud maximum because that it the speed of an Rs232 connector. The output of the comparator goes into the rs232 cable. The group also considered the availablity of software which may not be able to have one way communication. It may be that two way communication will be required. Further investigation into available software must be performed.
 +
 +== Week 10: November 3-7 ==
 +
 +Progress was made in the communication front. A major problem with using existing communication methods for the optical system is that most require both communicating devices (the laptops) to send and receive the data because of handshaking protocols. In other words, the sending laptop cannot simply send a signal, but will also by default receive a signal from the other laptop so corrections can be made for lost bits. The optical system as it is currently, however, cannot handle this, since the laser pointer end can only send, and the phototransistor end can only receive.
 +
 +A basic test using a female-to-female RS-232 cable showed that it could be ports could be shorted to make the computer handshake with itself during transfer. The idea would then be to trick the sending computer in to thinking the receiving computer had sent back the required signals. This worked successfully, though the wiring job connection ports on the RS-232 cable may need some work since the connections were loose. This testing was done in HyperTerminal, which has come bundled with any version of Windows since 1998 at least. While text could be sent by this method, sending a file through the application was not successful. The problem is that HyperTerminal's file transfer is set up so a file can be sent when the sending computer is on the sending screen, and the receiving computer is on the receiving screen. In other words, one computer cannot handshake to itself because it cannot simultaneously have the send and receive screens open.
 +
 +This leads to using a C program with serial port libraries to perform this instead. Using this, the computer can be tricked into thinking a handshake has occurred much more easily. There are many free examples online of C code that can be used to transfer files by serial port, so by understanding how they were, modifications can be made so the sending can be done without requiring receiving. This would also be good since it would allow the design of a GUI for the program that more clearly matches the goals of the project.
 +
 +On the hardware end, if too large a current enters a computer by the serial port, there is a chance it can do damage to the motherboard of the computer. This, in combination with the rarity of serial ports in modern laptops, leads us to use a USB to serial port adapter, since this will also limit current automatically, instead of designing more circuitry to do the same job.
 +
 +We had an extended talk about synchronicity in the circuit: if the frequency in which the data is sent will be the same as when it is received. In theory, if there is any delay in transmit, all of the signal will suffer the same lag, and so the receiving end will be at the same frequency. However, if there is a variable delay depending on the state sent, then a clocking mechanism will need to be employed on the receiving end to realign the data to the set frequency of the receiving laptop.
 +
 +The electronics of the circuit may have to be modified for the final design as well. In the lab, we have access to a voltage source that can provide a positive or negative voltage, but for the final demonstration we need it to run on batteries that will not be able to achieve this naturally. Instead, a current pump will need to be added to offset the DC voltage of the battery in the way we need.
 +
 +Next week, we plan to send and receive a text signal using HyperTerminal between two computers using our free space optics to send the data by laser. Also, preliminary programming will be done in C to control the serial ports of the sending and receiving laptops.
 +
 +== Week 11: November 10-14 ==
 +
 +The sending end of the circuit was modified such that it would send a 0 as a high voltage, and a 1 as a low voltage, opposite of intuitive. The advantage this inversion is that the laser will be on when no data is being sent, making alignment with the telescope end more possible.
 +
 +Freeware software called "Realterm" was obtained from Sourceforge.com for sending data and files by serial port without any protocol (handshaking that would require sending back and forth).
 +
 +On Friday, the FSO system successfully transmitted a 500kb picture from across the lab at a 38400 baud rate in under 5 minutes. Higher baud rates were tested with text and pictures, and found to work up to a standard baud rate of 57600. Non-standard baud rates can be chosen in Realterm, though 57600 or 38400 is sufficient for our project, and most likely safer.
 +
 +The rest of the work on the project will work on moving the project outdoors. The challenges ahead are mounting methods for the telescope and laser, as well as power solutions for our project (since power supplies are used currently).
 +
 +
 +**Nov 24**
 +
 +
 +In the last week, the group was experimenting with USB powering for their circuit. A Max 232 chip with capacitative voltage increasing was used to go from 5 to 9V. A second laser pointer and a NAND gate(which is part of the MAX 232 chip) were also implemented. The addition of the chip has not yet been sucessfully tested.

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