Boost Converters are a type of switch power supply that magically turns a small DC voltage into larger DC voltage. Learn about how that magic is preformed here. Used properly they are great, but the magic of a boost converter does have it's limits.
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For the measurement setup a Keithley 2230 power supply is set to 1.5VDC (think AA battery voltage) to act as V(in) for the boost converter. A Keithley DMM7510 HiRes multimeter is used to measure the ripple on V(out). A Keithley 2450 SourceMeter SMU is used to simulate a load on the boost converter in static and swept mode. The Keithley 2450 also produces a V(out) graph under the swept load.
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The video shows how the 5VDC boost converter starts performing poorly at loads close to 100mA. The output voltage begins to drop and ripple frequency increases as the boost converter works harder under the higher loads. The Keithley 2450 is set up to graph the boost converter voltage output as it simulates the swept load.
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[EDIT: February 20, 2016]: We got a comment that the boost performance could have been effected by not having a constant 1.5VDC input into the converter during the entire load sweep due to lead resistance. Turns out the comment was correct. We retested the same boost converter with 4-wire measurement connections at both the INPUT and OUTPUT. This 4-wire setup reduces any errors due to lead resistance. The video below shows the improved result. Measurement setup is everything!!!
Objective:
Build a robot that automatically tracks a user provided compass heading. Create a proof of concept indoor model and then scale up for outdoor use.
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If you are not interested in the build details and just want to see the result take a look at the video below. Basically, we are using an Arduino Nano and a LM303DLHC Micro Electro Mechanical (MEMs) compass sensor to read and track a compass bearing.
Rev 2.0: Uses the battery for the mounting chassis:
As shown in the videos, the robot continuously reads it's current compass bearing and adjusts to track the desired user direction. It does this by turning the wheel motors on or off. To keep things simple, the two motors are powered at full speed (no PWM). The two motors are never on at the same time.
----- Components:
Modern technology keeps the BOM small and puts the magic in the software that is shown later.
Ardunio Nano microcontroller for the brains. About $10USD if you shop around.
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LM303DLHC MEMs sensor provides the magnetic compass reading input for the Arduino. The LM303DLHC is has tilt compensation and accelerometers on board that can be used to detect hitting obstacles. About $7USD shipped from "eBay China".
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754410NE H-Bridge to drive the motors. (The Ardunio can't source enough current to drive the motors.) At is stands now the project only powers the drive wheels to move forward, however; we selected the 754410NE because with just a few wires and lines of code it can drive both motors forward and reverse. About $3USD.
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Get the above parts, a breadboard, two DC motors, wheels, a power source, etc. and hook it all up. In the diagram below I tried to closely mimic the breadboard setup in the pics:
----- Scaling Up:
We have a few APEX PA74 op amps that are capable of driving VERY high current loads. We are in the process of scaling the build for outdoor use with strong 12VDC motors. Here is a quick demo vid of the platform in action:
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If you are still with us, here is the Arduino Nano code. This is the most simple example. Other options include using the accelerometers to detect obstacles and drawing patterns (triangle, square, out and back, etc.)
Program Rev History and Notes:
Special thanks to pololu.com! See their GitHub site.
Point robot in desired direction then press reset button.
Put robot on ground. After 5 sec delay the robot will track the desired bearing.
This version moves the robot on the user desired bearing forever.
Other versions detect objects (bump) and draw patters (out and return, box, triangle)
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*/
// Define Variable Types and include.h
#include <Wire.h>
#include <LSM303.h>
int LeftWheel = 11; //left motor on output D11
int RightWheel = 10; //right motor on output D10
//**************************************
LSM303 compass;
int gotoheading; //global var for the initial robot direction. Or Press reset button...
void setup() {
pinMode(LeftWheel, OUTPUT); // sets the digital pin as output
pinMode(RightWheel, OUTPUT); // sets the digital pin as output
//read the direction that you want the robot to go. LM303 Header pins point to direction
compass.read();
gotoheading = compass.heading((LSM303::vector){0,-1,0});
delay(5000); // dealy xx mSecs after power up before doing anything
// Calibration values. Use the pololu.com Calibrate example program to get the values for your compass.
compass.m_min.x = -872; compass.m_min.y = -757; compass.m_min.z = -212;
compass.m_max.x = +461; compass.m_max.y = +511; compass.m_max.z = 844;
}
void loop() {
compass.read();
int heading = compass.heading((LSM303::vector){0,-1,0});
///* Print to the PC monitor. Debug only.
Serial.print(gotoheading);
Serial.print(" Current is: ");
Serial.print(heading);
//*/ //End Serial print to PC comment block
if (heading > gotoheading) //turn the bot left by turning on right motor
{
digitalWrite(LeftWheel, LOW);
digitalWrite(RightWheel, HIGH);
Serial.println(" OFF -- ON");
}
if (heading <= gotoheading) //turn the bot right by turning on left motor
{
digitalWrite(LeftWheel, HIGH);
digitalWrite(RightWheel, LOW);
Serial.println(" ON -- OFF");
}
