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Overview

The swarm robot project has gone through several phases, with each phase focusing on different aspects of swarm robotics and the implementation of the project. This entry focuses on the most recent phase of the project, covering topics such as, but not limited to, Xbee Interface Extension Boards, LED light boards, and changes made to the Machine Vision Localization System, and the overall conversion to LED boards and a controlled light environment. These entries help provide insight into setup and specific details to allow others to replicate or reproduce our results, and to provide additional information for those working on similar projects or this project at a later time. Other articles in the Swarm Robot Project category focus on topics such as the swarm theory and algorithms implemented, as well as previous phases of the project, such as motion control and consensus estimation. You may reach these articles and others by following the category link at the bottom of every page, or through this link - Swarm Robot Project.

Hardware

XBee Interface Extension Board

Previous Version

e-Puck with previous board

Current Version

Previous Version

The previous version of XBee Interface Extension Board, designed by Michael Hwang. Its configuration is shown in the figure on the left, with an actual image of the board mounted on an e-Puck seen in the figure on the right. This version of XBee Board does not contain a color sensor in it. Details about this version of XBee Interface Extension Board, such as parts used and Traxmaker files can be found on the Swarm Robot Project Documentation page.

Current Version

The upgraded version of XBee Interface Extension Board. It is designed by Michael Hwang. This version has a color sensor circuit built in. The details of the color sensor circuit can be found in the color sensor section below.

The RTS flow control line on the XBee is connected to the sel3 line of the e-puck. Although the CTS line is not connected to the sel2 pin in this board design, it can be easily connected with a jumper.

This new version of XBee Interface Extension Board design was actually built and implemented on the e-puck # 3. In order to see if there is any working problem in this board design, it is first tested with the other e-puck which uses the previous XBee Boards.

The e-puck # 3 upgraded with the new XBee board did not show any problem in communicating with other e-pucks. According to the goal defined, all e-pucks, including e-puck # 3, locate themselves to the desired location.

Color Sensor Circuit

Red Color Sensor Circuit

Green Color Sensor Circuit

Blue Color Sensor Circuit

As you may draw from the circuit diagrams above, as each photodiode receives light, a certain amount of current start to flow through the photodiodes and generates a voltage across R₁ = 680K. Each photodiode is designed to detect the certain range of wavelength of the light, and the amount of current flowing through the photodiodes is determined according to the amount of the corresponding light to each photodiode. The op-amp (LMC6484) takes the voltage generated across R₁ as the input signal, amplifying it by a ratio particular to the circuit. This ratio is also known as gain, and is defined by resistance of the potentiometer. The now amplified output is then sent to the analog digital converter, which on the e-Puck had been used as the X,Y, and Z axis accelerometers. This convenient, as each accelerometer axis can be used as a channel for the color sensors three colors. The converted signal can then be used to measure the response of the color sensor to light. The corresponding equation for the circuits illustrated above are as follows:

$|V_{o}|=|V_{i}*{\frac {R_{2}}{R_{pot}}}|$

• R_pot = resistance of the potentiometer (shown in the

diagram)

• R₂ = 100K (shown in the diagram)
• V_i = voltage across R₁ = 680K, which the op-amp

takes as an input

• V_o = output signal amplified from the op-amp

The gain of the color sensor circuits is approximately 20. Thus, the input voltage, V_i, is amplified to be 20V_i, which is V_o. As mentioned above, the gain can be adjusted properly by controlling the resistance of the potentiometer.

As shown in the circuit diagram on the left, the siganl from the red photodiode goes into the pin #5, and the amplified signal is sent out through the pin # 7. Similarly, the signal from the green photodiode goes into the pin #3 and it is sent out from pin #1 while the signal from the blue photodiode goes into the pin #12, and it is sent out from pin #14.

Output Pins

• Pin #7 - Amplified Red photodiode signal
• Pin #1 - Amplified Green photodiode signal
• Pin #14 - Amplified Blue photodiode signal

Parts used

Parts used in both the previous version and the new version of XBee Interface Extension Board

• 2x 10 pos. 2 mm pitch socket (Digikey S5751-10-ND)
• LE-33 low dropout voltage regulator (Digikey 497-4258-1-ND)
• 2.2uF tantalum capacitor (Digikey 399-3536-ND)
• 2x Samtec BTE-020-02-L-D-A (Order directly from Samtec)
• 0.1"header pins for RTS and CTS pins (you can also use wire for a

permanent connection)

• 2x 0.1" jumpers for connecting RTS and CTS pins if you used header

pins(Digikey S9000-ND)

Additional parts for new version of XBee Interface Extension Board

• 3x 100K resistors
• 3x 680K resistors
• 3x 10K potentiometer
• 3x 5pF capacitor
• 1x RGB color sensor (Order directly from HAMAMATSU, part#:s9032-02,

[http://jp.hamamatsu.com/resources/products/ssd/pdf/s9032-02_kspd1067e03.pdf Datasheet])

• 1x High impedence op-amp LMC6484

Future modifications

As mentioned in the overview, the black dot patterns of e-pucks are replaced with new LED patterns by implementing LED pattern board at the top of each e-puck. Thus, in order for the color sensor to collect data properly, it is necessary to move the color sensor from the XBee Interface Extension Board to the LED pattern board so that nothing will block the color sensor. All other components for the color sensor circuit remains in the XBee Interface Extension Board and only the color sensor will be place in the LED pattern board. We can use a jumper to connect the color sensor placed at the LED pattern board to the color sensor circuit place in the XBee Interface Extension Board. The datails of this LED pattern Board will be presented at the section below.

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LED Pattern Board

This new LED pattern board is introduced for the Swarm Robot Project. Currently, the unique black dot pattern of each e-puck was used for the machine vision system to recognize each e-puck. However, this black dot pattern requires a white background in order for the machine vision system to recognize e-pucks. The new LED pattern board uses LEDs with the proper brightness, instead of the black dot pattern. By doing so, the machine vision system can now recoginize e-pucks on any background. The reason why this LED pattern is recognized on any background will be presented briefly in the Code section below. In addition, in order to apply this LED pattern to the machine vision system, we made a modification in code. This modification will also be presented in the Code Section below. The PCB file can be downloaded here: Media:LED_Pattern_Board.pcb

LED Pattern Board Design

This LED Pattern Board is created using Traxmaker. This LED Board design can be downloaded here: Although we replaced the black dots with LEDs, we maintain each pattern of dots. The horizontal distance and the vertical distance between the two adjacent LEDs are both 0.8 inch. In order to reduce power consumption of the e-puck battery, we implement a seperate pair of AAA batteries to supply power to the LEDs. This LED board can be turned on and off by the switch. The milicandela rating of the LEDs used is 4850 mcd. In addition, this LED has diffused lens style. The reason to choose this LED is that it has a proper brightness and power consumption, and it is diffused so that the machine vision system can capture this LED in any places.The resistor used are 68.7 ohm.

As mentioned in the XBee Interface Extension Board section, the color sensor has to be moved to this LED pattern board from the XBee Interface Extension Board so that nothing blocks the sensor. Thus, as you can see in the Figure on the left, the color sensor is place at the front, and each photodiode is connected to the 10 pin header. This header connects the color sensor on the LED pattern board to the remaining part of color sensor circuit on the XBee Interface Extension Board.

Parts used

• 3x LED (Digikey 516-1697-ND): Some e-pucks require 4 LEDs since they

have a pattern composed of 4 dots

• 3x 68.7 ohm resistors : Some e-pucks require 4 resistors since they

have 4 LEDs

• 2x AAA Battery Holder (Digikey 2466K-ND)
• 1x Switch (Digikey CKN1068-ND)
• 1x RGB color sensor (Order directly from HAMAMATSU, part#:s9032-02)
• 1x 10 pos. 2 mm pitch socket (Digikey S5751-10-ND)

Tests

LED Distance vs Color Sensor Signal

Tests need be done in order to note the affect of the LED light on the color sensor due to potential interference. The first experiment performed is designed to see how much interference will be caused as the distance between the LED and the color sensor changes.

Setup and Results

1. A white LED is used in this experiment because the white LED will cover the entire wavelengh ranges of the visible light. The experiment with the white LED can yield a general result, while the experiment with the colored LEDs will yield more specific result focused on the interference between the certain photodiode and the certain color.

• LED: 18950 mcd (millicandela), digikey part number:

C503B-WAN-CABBB151-ND

2. The experiment was performed under the two conditions; with the ambient light and without the ambient light.

3. The LED and the color sensor were placed at the same plane, and both are facing upward.

4. Distance between the color sensor and the LED is increased by 0.25 inch each time from 1 inch to 2.5 inch.

5. The amplified output, V_o as shown in the circuit diagram above, of each photodiode is measured.

With Ambient light

• Unit: Volt, V

Distance vs Amplified Output

Distance	R	G	B
No LED	1	1.4	0.469
1 inch	1.259	1.716	0.832
1.25 inch	1.185	1.619	0.757
1.5 inch	1.135	1.529	0.669
1.75 inch	1.097	1.503	0.613
2 inch	1.086	1.481	0.589
2.25 inch	1.071	1.47	0.563
2.5 inch	1.06	1.453	0.546

Without the Ambient Light

• Unit: Volt, V

Distance vs Amplified Output

Distance	R	G	B
No LED	0.028	0.025	0.019
1 inch	0.244	0.221	0.223
1.25 inch	0.195	0.166	0.143
1.5 inch	0.162	0.123	0.097
1.75 inch	0.130	0.097	0.069
2 inch	0.102	0.077	0.054
2.25 inch	0.087	0.064	0.045
2.5 inch	0.073	0.056	0.039

As you can see in the two graphs above, the color sensor is affected by the light from the LED. The color sensor is most affectd by the LED when the LED is closest to it. As the distance between the LED and the color sensor increases, the interference decreases. When the color sensor is most affected by the LED under the presence of the room light, the output increases up to 25.9%, 22.6%, and 43.6 % of the original output. As the LED is 2.5 inch away from the color sensor, the output becomes very close to the original value. In this experiment, we see that the lights from LEDs can affect the color sensor. However, we used much brighter LED in this experiment than the ones we use in the LED pattern board. The brightness of the LED used in the experiment is 4 times larger than the ones in the LED pattern board. Thus, more experiment with the LEDs used in the LED pattern board is required.

LED Angle vs Color Sensor Signal

The second experiment is designed to see how much interference will be caused as the angle between LED and color sensor changes. Different from the first experiment, V_i, the voltage before amplified, is mesured since amplified output, V_o, easily reaches to the maximum.

Setup and Results

1. A white LED is used again in this experiment with the same reason above for the first experiment.

• LED: 18950 mcd, Digikey part number: C503B-WAN-CABBB151-ND

2. The experiment was performed under the two conditions; with the ambient light and without the ambient light.

3. In this experiment, the distance between LED and color sensor is kept constant, 1 inch.

4. Angle between LED and color sensor is increased by 15