Figure 1: Secondary GPS System Components – These are the components used in the secondary GPS system including, starting from the left, a 15.5” V2 Rubber Duck Antenna, a Micro-Trak 300, and a Garmin 18x GPS receiver.
Week of February 4th
The tracking system being used for our secondary payload is a Micro-Trak 300 (MT300) which consists of a TinyTrak3 controller chip and a Radiometrix 2 meter transmitter. The MT300 will be used along with a Garmin GPS 18x receiver and a V2 15.5 inch rubber duck antenna, see Figure 1.
The MT300 that our team is using has been used for previous projects. Unfortunately, previous teams were rough with the leads on the MT300 where the DB-9 connector interfaces with it; the leads, seen on the right side of the board in the picture above, were completely removed from the board. We tried to solder wires to the small lead holes next to the lead pads on the board, which had some leads previously soldered into them, but some sort of plastic had been melted onto the lead holes. After carefully removing the plastics with the use of an exactor knife and a magnifying glass, we were still unable to connect wires to the lead holes; the solder would not take to the holes.
We are thinking about drilling small holes through the lead holes in the board to feed wires through and solder the wires to the pcb lines. We have emailed Dr. Jacobs (a professor at EMU that teaches upper level electronics) to consult with her before taking this step.
Week of February 11th
Justin met with Dr. Jacobs on Feb. 11th to discuss the MT300. Dr. Jacobs agreed that the circuit board was nearly unsalvageable and approved our decision to attempt to drill new leads into the board. We used a Dremel tool with a very fine drill bit to bore the original holes. We were able to make relatively small holes into the board, fed wire through, and soldered the wires to the board. We performed a continuity test; however, the attached wires did not make a good connection. We resolved to replace the part. Dr. Pawlowski will be ordering a TinyTrak3Plus (TT3+) kit that we will construct and try to interface with the Radiometrix transmitter from the scrapped MT300 and the Garmin GPS receiver.
The tracking system being used for our secondary payload is a Micro-Trak 300 (MT300) which consists of a TinyTrak3 controller chip and a Radiometrix 2 meter transmitter. The MT300 will be used along with a Garmin GPS 18x receiver and a V2 15.5 inch rubber duck antenna, see Figure 1.
The MT300 that our team is using has been used for previous projects. Unfortunately, previous teams were rough with the leads on the MT300 where the DB-9 connector interfaces with it; the leads, seen on the right side of the board in the picture above, were completely removed from the board. We tried to solder wires to the small lead holes next to the lead pads on the board, which had some leads previously soldered into them, but some sort of plastic had been melted onto the lead holes. After carefully removing the plastics with the use of an exactor knife and a magnifying glass, we were still unable to connect wires to the lead holes; the solder would not take to the holes.
We are thinking about drilling small holes through the lead holes in the board to feed wires through and solder the wires to the pcb lines. We have emailed Dr. Jacobs (a professor at EMU that teaches upper level electronics) to consult with her before taking this step.
Week of February 11th
Justin met with Dr. Jacobs on Feb. 11th to discuss the MT300. Dr. Jacobs agreed that the circuit board was nearly unsalvageable and approved our decision to attempt to drill new leads into the board. We used a Dremel tool with a very fine drill bit to bore the original holes. We were able to make relatively small holes into the board, fed wire through, and soldered the wires to the board. We performed a continuity test; however, the attached wires did not make a good connection. We resolved to replace the part. Dr. Pawlowski will be ordering a TinyTrak3Plus (TT3+) kit that we will construct and try to interface with the Radiometrix transmitter from the scrapped MT300 and the Garmin GPS receiver.
Week of February 18th
We received the TinyTrak3Plus (TT3+), see Figure 2, and began its construction. Scott and Justin assembled the TT3+ and performed a continuity test across the board; there were no connection issues in the circuit. We programmed the TT3+ using the configuration software TinyTrak3Config v1.4, as seen in Figure 3, and a null modem connector. We made a null modem connector using two male DB-9 connectors.
We received the TinyTrak3Plus (TT3+), see Figure 2, and began its construction. Scott and Justin assembled the TT3+ and performed a continuity test across the board; there were no connection issues in the circuit. We programmed the TT3+ using the configuration software TinyTrak3Config v1.4, as seen in Figure 3, and a null modem connector. We made a null modem connector using two male DB-9 connectors.
We used a breadboard to interface between the TT3+ and the Radiometrix transmitter. We traced the wiring on the old MT300 between the TinyTrak3 microcontroller chip and the Radiometrix transmitter and compared it to the schematic of the TT3+ to determine the wiring for the interface.
During testing, the TT3+ was able to get gps lock; however our ground station did not receive any data from our call sign. The lights on the TT3+ indicated normal operation, though.
Week of February 25th and March 4th
Justin emailed Radiometrix and Byonics and asked about the wiring for interface between the TT3+ and the Radiometrix transmitter. Radiometrix suggested reviewing the schematic from the MT300, which was helpful for better understanding the circuit design and layout but did not yield any improvements for the interface. Byonics informed us that we need to bias the audio input on the transmitter to ½ VCC and couple the audio with a capacitor (they generally use a 0.1 mFd capacitor for 1200 Baud audio).
After reviewing the schematic for the TT3+, we found the voltage output for the DB-9 connector to the radio is equal to the input voltage for the TT3+ and not regulated. So Justin used a male DB-9 with soldered jumper wires for all the appropriate outputs from the TT3+ to the breadboard to interface with the transmitter except the V+. Since the V+ output to the GPS is 5 V regulated, Justin setup a parallel circuit to use the 5 V regulated output to power the transmitter, as well, and used a voltage divider to provide 2.5 V regulated to the audio input on the transmitter.
We were still unable to receive any signals from our TT3+ on the ground station. In the interest of time, we have decided to set the TT3+ aside for now and try to get a Micro-Trak 8000 FA (MT8000FA) unit to work with our setup, see Figure 4.
During testing, the TT3+ was able to get gps lock; however our ground station did not receive any data from our call sign. The lights on the TT3+ indicated normal operation, though.
Week of February 25th and March 4th
Justin emailed Radiometrix and Byonics and asked about the wiring for interface between the TT3+ and the Radiometrix transmitter. Radiometrix suggested reviewing the schematic from the MT300, which was helpful for better understanding the circuit design and layout but did not yield any improvements for the interface. Byonics informed us that we need to bias the audio input on the transmitter to ½ VCC and couple the audio with a capacitor (they generally use a 0.1 mFd capacitor for 1200 Baud audio).
After reviewing the schematic for the TT3+, we found the voltage output for the DB-9 connector to the radio is equal to the input voltage for the TT3+ and not regulated. So Justin used a male DB-9 with soldered jumper wires for all the appropriate outputs from the TT3+ to the breadboard to interface with the transmitter except the V+. Since the V+ output to the GPS is 5 V regulated, Justin setup a parallel circuit to use the 5 V regulated output to power the transmitter, as well, and used a voltage divider to provide 2.5 V regulated to the audio input on the transmitter.
We were still unable to receive any signals from our TT3+ on the ground station. In the interest of time, we have decided to set the TT3+ aside for now and try to get a Micro-Trak 8000 FA (MT8000FA) unit to work with our setup, see Figure 4.
Week of March 11th
The Micro-Track 8000 FA (MT8000FA) had also been misused and the lead pads for interface with a DB-9 connector had been stripped by a previous group from the circuit board. We try to resolve this issue by drilling new lead holes in the board as we did with the MT300 and soldering wires into the board for interface. After installing the wires we performed a continuity test and every checked out fine.
We programmed the MT8000FA, see Figure 5, using the MT8000FAConfig software and a null modem connector.
The Micro-Track 8000 FA (MT8000FA) had also been misused and the lead pads for interface with a DB-9 connector had been stripped by a previous group from the circuit board. We try to resolve this issue by drilling new lead holes in the board as we did with the MT300 and soldering wires into the board for interface. After installing the wires we performed a continuity test and every checked out fine.
We programmed the MT8000FA, see Figure 5, using the MT8000FAConfig software and a null modem connector.
We tested the MT8000FA and did not receive a signal on our ground station. After reviewing the literature for the MT8000FA, we learned that the small blue potentiometer, seen in the upper left portion of Figure 4, can be used to increase the gain of the signal sent by the transmitter. Justin made small adjustments on the potentiometer until a signal was received by the ground station. We then tested the limits on the gain for a received signal and set the gain.
We performed a GPS lock, accuracy, and range for the gps system test by walking around campus with the MT8000FA. The results of the test can be seen in Figure 6. Once we got gps lock, we were able to maintain the lock for the remainder of the test until we returned to the electronics lab.
We performed a GPS lock, accuracy, and range for the gps system test by walking around campus with the MT8000FA. The results of the test can be seen in Figure 6. Once we got gps lock, we were able to maintain the lock for the remainder of the test until we returned to the electronics lab.
Figure 6: Secondary Payload GPS Test – This is a screenshot of the gps test for the MT8000FA system as reported by the ground station on the APRS website (aprs.fi).
Week of March 25th
Justin constructed the payload for the MT8000FA using foam insulation. As an addition bit of fun, decided to enclose our secondary payload in a bunny rabbit stuffed animal, see Figure 7. The rabbit will be attached to the rest of the payload by a quick connector to the harness around his body. A zipper was added to the front of the rabbit to allow quick access to the MT8000FA system.