Prototype Ordering

So I've ordered a few prototype parts about a week and a half ago, got them in last week and hopefully ordered a PCB last Thursday. The main goal of this intermediate prototype step is to realize functionality of the daughter board, allow of some flexibility with the final design in seeing the prototype and possibly making changes, and finalize the sensors/actuators used.

Parts List

Ref	Desc	PN	Supplier	Price	QTY	Total		Explanation
RN1B	RES ARRAY 10K OHM 10TRM 8RES SMD	MNR35103CT-ND	Digikey	0.336	10	3.36		Pullups or pulldowns for the sensors or outputs
RN1	RES NET BUSSED 10K OHM 8-SIP	4608X-1-103LF-ND	Digikey	0.32	10	3.2		Alternate through-hole package for pullups or pulldowns
	CABLE ASSY R/A 2.5MM MONO 6'	CP-2202-ND	Digikey	2.61	5	13.05		Connection to sensors, board side
	CABLE ASSY R/A 2.5MM STEREO 6'	CP-2204-ND	Digikey	2.64	5	13.2		Alternate sensor connection, 3 pin
CN7-CN20	CONN JACK MONO RT ANG 2.5MM	CP1-2503AM-ND	Digikey	0.39	5	1.95		Cable to solder sensor to, 2-wire
CN1-CN6	CONN JACK STEREO RTANG 2.5MM	SPC21360	Newark	0.694	6	4.164		Alternate sensor cable, 3 wire
	CAP CER .1UF 50V Y5V 0603	490-1568-1-ND	Digikey	0.027	10	0.27		Analog input decouple cap, boardside
RN2, RN3	RES ARRAY 100OHM 16TERM 8RES SMD	MNR18101CT-ND	Digikey	0.095	10	0.95		Digital I/O current limit (series) resistors
					Total	40.144

I had to replace the 2.5mm stereo jack with one from Newark because it was out of stock at Digikey. It wasn't the same part at all, so I had to redesign the Eagle library part. I chose not to include the analog input filter caps for now on the board layout (so no reference), but will try out the board with and without and see if I need them in the final design. I have a feeling they won't do much either way.

Proto Board Circuit and Layout

Below is my prototype circuit and layout. I'm not sure where I could post the Eagle files, as these pictures are not going to be that great for anyone wanting to make their own.

The layout.

The layout above has the ground planes "ripped up" for easier viewing, but the actual board has a top and bottom ground plane filling in most of the white space. This helps reduce noise and reduce power supply impedance (usually a bad thing in embedded projects).

An annotated, explained version of the board layout is shown below in fashionable colors.

Next post will be about the details of soldering up the connectors to the actual sensors/actuators. Stay tuned.

~JWilly

Arduino Duemilanove

http://arduino.cc/en/Main/ArduinoBoardDuemilanove

Summary

Microcontroller	ATmega328 (datasheet)
Operating Voltage	5V
Input Voltage (recommended)	7-12V
Input Voltage (limits)	6-20V
Digital I/O Pins	14 (of which 6 provide PWM output)
Analog Input Pins	6
DC Current per I/O Pin	40 mA
DC Current for 3.3V Pin	50 mA
Flash Memory	16 KB (ATmega168) or 32 KB (ATmega328) of which 2 KB used by bootloader
SRAM	1 KB (ATmega168) or 2 KB (ATmega328)
EEPROM	512 bytes (ATmega168) or 1 KB (ATmega328)
Clock Speed	16 MHz

Schematic & Reference Design

EAGLE files: arduino-duemilanove-reference-design.zip

Schematic: arduino-duemilanove-schematic.pdf

Component Testing

• Spectra Symbol flex sensor
  Type: Resistive
  0 deg bend: ~8k ohm
  180 deg bend: ~16k ohm
  
  
• Vibe motor (manu?)
  Seemed like the operating voltage range was between:
  1.5V@60mA - 3.0V@200mA
  -> The motor would quickly heat up (within 10 secs) while running at 3V
  -> Can the Arduino supply this much?
  
  
• Regal mini speaker
  8 ohm, 0.1 W
  Very good high freq. response @ 1 Vpp
  
  
• Crouzet SSR - M-0ACS-315, ELE-0937
  Input: 3.0V@3mA - 8.0V@27mA (15mA@5V)
  Output: 1A, 24-140 VAC
  Freq Response: Start to see roll-off @ ~1MHz
  
  
• Thermister - 103 (?)
  Normal Temp (~70 deg): R = ~10k
  Between fingers for 10 secs: R = 7.3k
  
  
• Photoresistor
  Completely dark: ~1 Mohm
  Indoor flourescent light: ~700 ohm
  Finger over device while indoors: ~4k ohm

Connector Search

Almost all my components are 2-conductor.
Exceptions are:
-IR rangers
-Pots
-Multi-colored LEDs

I'm thinking because this is the case, and because we have limited board space, I was going to use 2.5mm submini phone jacks and plugs for connecting all the sensors and actuators.




Pros:

• I can buy them in mono or stereo, giving 2 or 3 conductors each.
• I can buy the cable assemblies already made up for ~2.60 ea. Then I will only need to attach the sensor/actuator, plus an inline resistor for some sensors that require it.
• I can also buy very small jacks that are either SMT or through-hole, allowing for 14 digital I/O and 6 Analog inputs.

Cons:

• Just like headphones, the molded plug can become loose on its wires, possibly loosing connection.

Another option would be to use board connectors, similar to what is used for connecting computer fans to motherboards, or really any board to board connection. Only problem with these is that the crimp-style wire connection tends to be a little fragile.

Tomorrow will be tracking down one or two more solutions so that I can order these to have a mock-up, and also to get a feel for the durability of these solutions.

~JWilly

The beginning...

The goal of this project is to develop the Tangible Experience Design course here at RIT to better enable Industrial Design students to grasp real-world programming techniques by controlling a microcontroller and sensors and actuators. The task that I, the electronics specialist, must do is to design the base for students to work on, removing some of the engineering aspects to allow the students to focus on control through programming.

The Arduino Duemilanove ATmega328 Starter Kit was chosen to be the central microcontroller board, with sensors and actuators plugging into a daughter board, electrically connected to either the Analog inputs or the Digital outputs. Some simple "glue" circuitry will be required to interface all the sensors to the microcontroller's inputs.

Arduino

From http://www.sparkfun.com
Starter Kit for Arduino - Flex (DEV-09905) 1 @ $59.95
http://www.sparkfun.com/commerce/product_info.php?products_id=9905

Not all of the components seen in the picture will be used for this project, but I'm not setting boundaries at this point.

Development Requirements

• Transparency – able to see inside enclosure

• Easy connect/disconnect of sensors, actuators

• Students won't be building on breadboard, just plugging components into a shield (daughter board)

• 120VAC Plugs + relay contained/shielded for safety

1. SSR Relay – AC plug unit

2. Easy connections for sensors + actuators

3. Sensors

• Pressure (Analog)

• Flex sensor (Analog)

• Photoresistor (Analog)

• Thermistor (Analog)

• Switches (Digital)

• IR Rangers (Digital?)

• Potentiometers (Analog)

4. Actuators

• Speaker (Digital, PWM)

• Vibe motors (opt) (Digital, PWM)

• LEDs (Digital, PWM)

• SSR + wall plug (Digital, PWM)

The current collection of sensors and other assorted materials is shown in the picture below. What these are to do is still up in the air. Also, a rough sketch of the Arduino board with a daughter board on top (usually called a shield, for some odd reason), with an idea of the interconnect to sensors/actuators.

Tomorrow's task will be to nail down a solid system structure, find interconnects, and characterize the sensors and actuators.

~JWilly