On October 3rd (Friday), the N.M.E. design had a meeting with Dr. Ducharme to discuss the progress on our senior Design project at 1:00p.m. After the meeting our team continued our work on campus at the Engineering 2 building in room 180. Due to our previous attempt at making our op-amp circuit for the K-type thermocouple, our goal that day was to start from scratch and use the necessary tools within the lab to rebuild our circuit. On the first attempt of building our op-amp circuit (on 09.28.2008) we were unsuccessful because we didn't have the right accessories. For example, we purchased a circuit board that had to have the components soldered to it and the solder tip that we were using was a little bit dull, but it was still fully functional. Our digital multi-meter was also giving us problems, because it would give us wrong readings. A major issue that we also came across during this attempt, was we were unable to get a hold of a 100-ohm potentiometer so we had to make use and create one out of several resistors to be equivalent to that value. With all these factors revolving around us we miscalculated the time it would take to get it finished. And yes, it did take longer than expected and at the end of the day the 1st attempt of our op-circuit for the thermocouple was unsuccessful. (Aside note: A Thermocouple creates a voltage of its own.)
So on this day we had a better chance to get things finished correctly in a timely manner, because we had the necessary equipment and materials that were needed. We had full- access to the soldering irons, breadboards, variety of different value resistors, power supply, and digital multi-meters. So our team continuted with the 2nd attempt of constructing the op-amp circuit for the thermocouple. We followed the schematics and pinouts according to the LT1025 and LT1050. Our first problem we encountered, was wiring the necessary components to the correct op-amp. This problem was fixed just by simply switching the op-amps to their designated side. A factor that made our team's process alot easier this time around was using a breadboard. By using the breadboard it was very easy to replace components and less time consuming to troubleshoot. The fact that we didn't need to solder anything on the 2nd attempt was a big help. As we were constructing our circuit we came across a problem that involved our LT1025 255k ohm feedback resistor. The voltage reading coming from the thermocouple would highly depend on the value we would substitute for our feedback resistor to the LT1025. We did numerous attempts of replacing different value resistors in the circuit. But even with the assigned 255k ohm resistor it would give us miscalculated values (temp./voltage) readings. We went ahead and kept lowering the resistor values until our voltage readings were finally correct. The resistor value that we replaced with the 255k ohm resistor was a 127k ohm resistor. The equation that we used to determine the thermocouple's temperature in relation to the voltage readings was 10 milliVolts per degress Celsius (10mV / oC). The constructed op-amp circuit for our Exhaust Gas Temperature Thermocouple was SUCCESSFUL.
On October 5th (Sunday), the N.M.E. design group met to start the schematics for our printed circuit board, Bill of Materials, and operation of the servo. Our team is using the expressPCB program which we downloaded from ExpressPCB.com to build our printed circuit board. Our printed circuit board will have the necessary components such as the Propeller chip, Op-amp circuit for the thermocouple, EEPROM, voltage regulator, Propeller plug, pins for the servo, LM34 temp. sensor, datalogger, and TV/RCA adapter, etc. All the necessary and required components like resistors, capacitors, etc. will be available in the final draft of the Bill of Materials.
We began operation testing on the servo. Rather than receiving the Futaba standard servo from Parallax, we ended up receiving the Futaba continuous rotational servo which was the wrong product we ordered. We decided that we needed a smaller scale servo in order for the servo to mount correctly in the R/C car. So in exchange, we called Parallax, they courteously resolved the problem and the outcome resulted in Parallax providing us with a complimentary GWS Pico servo at no charge. In the mean time our team has been working on the code for the servo. Until the GWS pico servo arrives we our currently testing with the standard servo from the R/C car. Our group is determing whether it is a better choice to have the servo operate by pulse-width or angles. So far we've accomplished movement of the servo by incrementing values in the code, but we're trying to figure out how we can reset the position in the designated angle by our demand.
Below is the comparison of our 1st (Top) & 2nd (Bottom) attempts of the op-amp circuit for the thermocouple
Below is the thermocouple bath we used to stabalize the thermcouple's temperature
Below is proof that as the thermoC. heat rises the voltage created from the thermoC. increases.
B. Justin Rosario
N.M.E. Design Team
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