F13: POV Display - Revision history

Proj user5: /* References */

2013-12-08T02:04:46Z

‎References

Proj user5: /* References */

2013-12-08T02:04:04Z

‎References

Proj user5: /* Parts List & Cost */

2013-12-08T02:02:50Z

‎Parts List & Cost

Proj user5: /* Hardware Design */

2013-12-08T01:56:07Z

‎Hardware Design

Proj user5: /* Hardware Design */

2013-12-08T01:49:35Z

‎Hardware Design

Proj user5: /* Hardware Design */

2013-12-08T01:47:54Z

‎Hardware Design

Proj user5: /* Hardware Design */

2013-12-08T01:40:46Z

‎Hardware Design

Proj user5: /* Hardware Design */

2013-12-08T01:36:40Z

‎Hardware Design

Proj user5: /* Hardware Design */

2013-12-08T01:31:43Z

‎Hardware Design

Proj user5: /* References */

2013-12-08T00:01:47Z

‎References

@@ Line 273: / Line 273: @@
 == References ==
-[1].http://www.identifont.com/similar?1SS
+[1] http://www.identifont.com/similar?1SS<br>
-[2] http://en.wikipedia.org/wiki/Persistence_of_vision
+[2] http://en.wikipedia.org/wiki/Persistence_of_vision<br>
-[3] https://github.com/cjbaar/LPD8806
+[3] https://github.com/cjbaar/LPD8806<br>
-[4] https://solarbotics.com/download.php?file=1889
+[4] https://solarbotics.com/download.php?file=1889<br>
-[5] http://www.wayjun.com/Datasheet/Led/5050%20SMD%20LED.pdf
+[5] http://www.wayjun.com/Datasheet/Led/5050%20SMD%20LED.pdf<br>
-[6] Preet's Sprinkler System Code
+[6] Preet's Sprinkler System Code<br>
 [7] [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Wireless/WiFi/WiFly-RN-UM.pdf Wifly User Manual]

@@ Line 273: / Line 273: @@
 == References ==
+[1].http://www.identifont.com/similar?1SS
-* Preet's Sprinkler System Code
+[2] http://en.wikipedia.org/wiki/Persistence_of_vision
-* [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Wireless/WiFi/WiFly-RN-UM.pdf Wifly User Manual]
+[3] https://github.com/cjbaar/LPD8806

@@ Line 55: / Line 55: @@
 | align="center" style="background:#f0f0f0;"|'''Part'''
 | align="center" style="background:#f0f0f0;"|'''Cost'''
 |-
 | Wifly RX-NV module||$35
@@ Line 60: / Line 62: @@
 | Web Hosting through iPage||$12
 |-
+| LPD8806 strips (2) Adafruit.com product ID: 306||$30
 |}

← Older revision		Revision as of 01:56, 8 December 2013
Line 144:		Line 144:

	[[File:CMPE240_F13_POV22_MechanicalDiagram2.jpg\|center\|frame]]		[[File:CMPE240_F13_POV22_MechanicalDiagram2.jpg\|center\|frame]]
		+
		+	<br>
		+	Pseudo Code for LED Drive Portion
		+	The main issue with the LPD8806 stem from the fact that its datasheet is available only in Chinese and the English translation is sorely lacking, especially in the details of communication with the device. The communication sequence was reverse engineered by previous users and is available at [3]. The task remaining is to adapt the library for the SJSU board and to write the code for the POV display according to its physical build. Since the first POV display’s motor was burned out, this pseudo-code concentrates on that of the second display, though the two codes are similar.
		+
		+	Initialize SPI bus
		+	Initialize LPD8806 Strip
		+	Initialize Font Map
		+	[Obtain string & num_char from WiFly Portion]
		+
		+	For (int j=0; j<=num_char; j++) {
		+	RenderChar(string[j], color);
		+	Turn off pixels
		+	Set spacing between characters with delay_us
		+	}
		+
		+	RenderChar(char, color) {
		+	Switch (char) {
		+	Case ‘A’: writechar(index, color); // index into Font Map for the character ‘A’
		+	…
		+	Case ‘Z’: writechar(index, color); // index into Font Map for the character ‘Z’
		+	Default: writechar(index, color); // index into Font Map for the space character
		+	}
		+
		+	Writechar(char,color) {
		+	For (col_index=0; col_index <col_index+5; col_index++) { // Font chosen 5 rows x 8 cols, though only 7
		+	For (row_index=0; row_index< 8; row_index++) { // is needed to display upper case letters
		+	Select pixel position according to PHYSICAL position on the strip
		+	If (Font map bit is 1) {
		+	Set_pixel(pixel position, color);
		+	Else
		+	Set_pixel(pixel position, color=0=OFF);
		+	}
		+	}
		+	Set spacing within character with delay_us
		+	}
		+	}
		+
		+	The font map is an 8-bit 1-dimensional integer array initialized according to the rotational direction of the rotor. In this case the rotor is rotating such that the vertical LED strip scans from left to right. To simplify matters for the first cut, the letters are of fixed width.

	=== Software Design ===		=== Software Design ===

@@ Line 112: / Line 112: @@
 |Power||4 x 1.5V AA batteries or 9V regulated to 5V
 |}
+<br>
 Figure 4 depicts the POV display that was initially crafted for this project to meet the requirements listed above.<br>
@@ Line 140: / Line 140: @@
 |Power||4 x 1.5V AA batteries or 9V regulated to 5V
 |}
+<br>
 Figure 5 depicts the POV display crafted.

@@ Line 98: / Line 98: @@
 | align="center" style="background:#f0f0f0;"|'''Detail'''
 |-
-Font to Display:			Figure 1
+|Font to Display||Figure 1
-Motor RPM			at least 375 rpm
+|-
-Motor torque			Dependent on mass of rotor, thus rotor needs to be as light as possible
+|Motor RPM||at least 375 rpm
-Bits per LED			24
+|-
-LEDs per display		32
+|Motor torque||Dependent on mass of rotor, thus rotor needs to be as light as possible
-SPI bus speed			at least 3.072 MHz
+|-
-Power				4 x 1.5V AA batteries or 9V regulated to 5V
+|Bits per LED||24
+|-
 Figure 4 depicts the POV display that was initially crafted for this project to meet the requirements listed above.<br>
@@ Line 115: / Line 122: @@
 This POV display is physically smaller so closer spacing of the LEDs is required.  To this end, the LED strips were sliced and arranged in rows with 2 LEDs per row as shown in the figure below.  This was necessary because each LPD8806 chip drives two LEDs and thus 2 LEDs is the smallest unit that the strip can be divided into.  Only one column is used as the active column, however.  In order to reduce weight and complexity, the number of LEDs was reduced from 32 down to 14, with 7 active LEDs.  One aspect of this design is that achieving torque and rpm would not be an issue as the blender motor is more than capable of driving the mass at 1500 rpm.  The requirements for this POV display are summarized below:
-Font to Display:			Figure 1
+{| {{table}}
-Motor RPM			1500 rpm minimum
+| align="center" style="background:#f0f0f0;"|'''Requirement'''
-Motor torque			More than sufficient to be of concern
+| align="center" style="background:#f0f0f0;"|'''Detail'''
-Bits per LED			24
+|-
-LEDs per display		7 active, 7 non-active
+|Font to Display||Figure 1
+|-
-SPI bus speed			at least 1.344 MHz
+|Motor RPM||1500 rpm minimum
-Power				4 x 1.5V AA batteries or 9V regulated to 5V
+|-
 Figure 5 depicts the POV display crafted.

@@ Line 80: / Line 80: @@
 [[File:CMPE240_F13_POV3_LEDstrip.jpg|center|frame]]
-Figure 3: Diagram of LED strips <br>
+Figure 3: Diagram of staggered LED strips <br>
 Initially, a personal blower was thought to be sufficient to provide the framework on which to build the POV display.  The rotating cylinder of blower has dimensions of 3” diameter x 5” tall.  This is sufficiently wide to display a single character; however, with the manageable sized cylinder came the small sized motor.  Since this motor was not intended to move anything but air, it does not have enough torque to move the combined weight of the board, LED strips, wires, and battery pack.  A motor with a higher torque is needed.

@@ Line 70: / Line 70: @@
 <br>
 '''Mechanical Requirements'''<br>
-The POV display requirements were necessarily derived from the dimensions of the LED strip and the dot matrix font that was chosen.  The strips chosen are Adafruit LPD8806 RGB strips, primarily because of their high refresh rate at 4000 Hz.  The font chosen is reproduced below in Figure 2 for discussion.<br>
+The POV display requirements were necessarily derived from the physical dimensions of the LED strip and the dot matrix font that was chosen.  The strips chosen are Adafruit LPD8806 RGB strips, primarily because of their high refresh rate at 4000 Hz[4].  The font chosen is reproduced below in Figure 1 for discussion.<br>
@@ Line 77: / Line 77: @@
 In order to display a single character, the display’s width should be a minimum of 5 pixels wide.  Using the LED strip’s dimensions as a starting point, the RGB pixels are 5050, meaning half a centimeter wide by half a centimeter tall, and are spaced 31 mm apart.  If the strip’s pixel spacing is maintained, then the display should be 6” wide as a minimum so that the viewer can see 5 pixels across.  If instead two strips of LEDs are used, with the strips staggered vertically so that the LED spacing is halved, then only a 3” minimum diameter is needed.
 [[File:CMPE240_F13_POV3_LEDstrip.jpg|center|frame]]
 Figure 3: Diagram of LED strips <br>
-Initially, a personal blower was thought to be sufficient to provide the framework on which to build the POV display.  The rotating cylinder of blower has dimensions of 3” diameter x 5” tall.  This is sufficiently wide to display a single character; however, with the manageable sized cylinder came the small sized motor.  Since this motor was not intended to move anything but air, it is not expected to have enough torque to move the combined weight of the board, LED strips, wires, and battery pack.  A motor with a higher torque is needed.
+Initially, a personal blower was thought to be sufficient to provide the framework on which to build the POV display.  The rotating cylinder of blower has dimensions of 3” diameter x 5” tall.  This is sufficiently wide to display a single character; however, with the manageable sized cylinder came the small sized motor.  Since this motor was not intended to move anything but air, it does not have enough torque to move the combined weight of the board, LED strips, wires, and battery pack.  A motor with a higher torque is needed.
 In addition to the higher torque, the motor needs to have sufficient speed.  POV displays work on the principle that an afterimage persists on the retina of the human eye for approximately 40 ms (1/25th of a second).  Therefore the motor must be able to spin a pixel a complete revolution in 40 ms or 25 Hz.  25 cycles per second translates to 1500 rpm minimum.
 Suppose now that the display is 12.6” or 32 cm in diameter.  If no horizontal spacing between the pixels are allowed, then that translates to pi*32 /0.5 = 201 pixels around the circumference.  The entire circumference must be refreshed in 40 ms to maintain persistence of vision.  When using a single strip, the LED must transition from one column to the next in 40ms/201 ~ 0.2 ms.  Therefore the minimum refresh rate needed for a display of this size is 1 / 0.2 ms = 5 kHz, slightly higher than the refresh rate possible with the LPD8806.  Therefore, some horizontal spacing between the pixels is required for a display of this size.  If a spacing of 1 pixel is used, then the refresh rate can be halved to 2.5 kHz.
 A display rotating at 1500 rpm that requires a high torque, high speed motor must be precisely machined to operate safely.  Since this is not possible within the self-imposed budget constraints of the project, we chose the best possible speed that can operate safely with manually crated components.  This motor is the 12V, 500 rpm motor from BatterySpace.com.
-Figure 4 depicts the POV display that was manually crafted for this project.<br>
+A display rotating at 1500 rpm that requires a high torque, high speed motor must be precisely machined to operate safely.  Since this is not possible within the self-imposed budget constraints of the project, we chose the best possible speed that can operate safely with manually crated components.  This motor is the 12V, 500 rpm motor from BatterySpace.com.  For “Saturday morning cartoon” quality POV, 500 rpm is sufficient since the same picture is used 2 to 4 times when running at 25 Hz[2], thus reducing the speed requirements by half to a quarter, and the 1500 rpm can be reduced to 750 down to 375 rpm.
 [[File:CMPE240_F13_POV4_MechanicalDiagram.jpg|center|frame]]
 Figure 4: Mechanical Diagram of POV display <br>
 === Software Design ===

← Older revision		Revision as of 00:01, 8 December 2013
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	== References ==		== References ==
		+
		+	* Preet's Sprinkler System Code
		+	* [http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Wireless/WiFi/WiFly-RN-UM.pdf Wifly User Manual]