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MAE Electronic Shop

Welcome to the MAE Electronics Lab home page:

Systems, sensors, circuits, ideas...

 



Facility Description

The MAE Electronics Laboratory is a resource providing support for student and faculty projects which may incorporate electronic elements including circuits, sensors and transducers, signal conditioning, data acquisition, embedded processors, control systems, and similar applications. The lab includes several work stations with a variety of bench instruments and equipment for building and testing circuits. We are always happy to provide discussion and consultation. The facility is managed by Steve Roberts. Please see his contact information below.

 


 

Work Station


       

One of the work stations available in the lab.

Shown are a couple of bench multimeters, an oscilloscope, multiple-voltage power supply, isolated AC supply, breadboard setup for testing circuit ideas.

 

 

 

Some projects I have designed/built:       

 

 Fast-response CO2/H2O analyser                        


 

This instrument uses an infrared source and a thermoelectrically cooled lead-selenide (PbSe) detector to simultaneously measure concentrations of carbon dioxide and water vapor in the atmosphere. Two narrow bandpass optical filters make the response specific to the CO2 and H2O molecules. A third filter is non-responsive to CO2 or H2O and provides rejection of common-mode errors. The three filters are mounted on a rotating wheel positioned in front of the detector. The wheel is driven at 3000 RPM, giving a basic 50 Hz response. The optical path from source to detector is a 20cm 4x folded path, giving an effective 80cm path length in a 20cm dimension. The instrument is typically used in conjunction with a sonic anemometer for eddy-covariance studies, designed to estimate vertical fluxes of CO2 and water vapor over vegetation or other surfaces. This is a common technique used by climate-change researchers.

 

 

Adhesive Tester


 This instrument was designed to quantify the bond strength of some adhesives. In use, a copper specimen is glued onto a copper base plate and the instrument pushes against the specimen until the bond fails, or begins to fail. At that point, the test can be continued to observe the failure dynamics, or the test can be concluded. The basic mechanism is a stepper motor which drives a leadscrew. Mounted on the leadscrew between the two pillow blocks is a load cell which continually senses the compression force. The control box contains signal conditioning for the load cell, a data acquisition subsystem, and a microprocessor system to control the stepper motor. Max and min photo-interrupters and microswitches are also included to prevent over-extensions of the lead screw. The processor also continually monitors the force on the load cell, and stops the test if maximum rated force is approached. A companion PC program receives and plots the force/extension data in real time, and saves the data file for further analysis. It is basically a mini-Instron© instrument, but without the $$$$$ price tag. 

 

 

Autonomous Sumo Robot


This robot was designed to compete in the 500-gram autonomous sumo robot class. The rules of the game are similar to human sumo, with the object being to push your opponent out of the competition ring. There are several competition classes, ranging from 25 grams to 3 kilograms and over. In the 500-gram class, the robot must fit into a box with dimensions of 10 cm on a side. The height is unlimited. The robots must be autonomous, and must be capable of movement (no bricks). A match is limited to 3 minutes, but most are over within 1-10 seconds. Any kind of locomotion is OK, but nothing can come off of the robot: water, powder, projectiles, and so on. This robot has two infrared distance sensors in front, one on each side, and one in the rear. The tactic is to sense an opponent as soon as possible, get in position to attack, and charge! The competition takes place on a black-surfaced ring, with a narrow white border. The white border allows the robot to sense when it is beginning to exit the ring. It must then take corrective action to avoid leaving the ring, and thus losing the match.

 


Here's a bottom view of the robot. The small circles at the two front corners are photodetectors which sense the transition from the black ring surface to the white rim of the ring. There are two motors. The motors are long, which required that they be placed side-by-side. This is a serious design compromise. The tradeoff was getting a robot which was pretty fast and powerful. The black square block is to limit how much the robot can rock back and forth on the wheels. The wheels were homemade, using a soft polyurethane mix which was poured into a mold around the aluminum wheel hubs. Grippy wheels are critical. Power source is an 11.1 volt  lithium-polymer battery pack located under the sloping front end. This robot won it's first (and only) contest! Overall, it was an interesting exercise combining mechanical design, electronics and sensors, microcontroller software, and just thinking through the competition tactics and encoding one's ideas into the software. Sumo anyone? 



Opamp Tester

 

Background: The MAE170 lab course at UCSD has several exercises involving operational amplifiers ("opamps"). When debugging a new circuit which doesn't work it's useful to have a quick way to test the amplifier. This opamp tester was designed for the “741” opamp, and should generally work for an opamp having the same pinout for pins 2,3,4,6, and 7. The offset adjustment pins 1 and 5 are not used. Pin 8 is no-connection (NC). Pins 1,5, and 8 are not used here.

Operation:  Insert your opamp into the vacant socket at the top of the board, between the two LEDs. Be sure to orient the opamp with pin 1 at the upper left of the socket, adjacent to the green LED. Press and hold the pushbutton. The tester will briefly flash both LEDs and will then begin the test. The green LED will typically flash three times as the test proceeds. At the end of the test a good opamp will be indicated by a solid green LED. A bad opamp will show a solid red LED. Once either LED comes solidly on, the test is complete. The test takes about 3 seconds.

How it works: A Microchip PIC12F683 microcontroller is programmed to produce a 20kHz PWM signal at three different duty cycles. The PWM is then passed through a low-pass  filter to give three different DC voltage levels. These voltages are amplified by the test opamp which is set up as a non-inverting amplifier with a gain of 3. The microcontroller samples each voltage in turn and checks to see if the opamp has correctly amplified each filtered PWM source signal. As each voltage is successfully detected the green LED briefly lights. If all three signals are correctly amplified and measured (green-green-green) the opamp passes the test and is assumed to be good. The green LED is then solidly turned on, and the test is complete. If any one of the three test voltages do not measure correctly the opamp fails the test, the test is immediately halted, and the red LED is solidly turned on.


 








 

 

Useful Electronics Links...                    A collection of links with useful schematics and data sheets.

 

Engineering Electronics Support Facility
Please contact Steve Roberts as follows:
 
email:                             steveroberts@.ucsd.edu
Voice:                            858-534-2421
Location:                       Mechanical/Aerospace Engineering
                                      EBU2-328   
 
 
 
It's 3AM and you've finally gotten your project working. Just remember:
"If it works, it's obsolete."
ą
Steve Roberts,
Apr 6, 2018, 3:21 PM
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