Power estimates

XBee Series 2
TX, RX Current: 40 mA (@3.3V)
Transmit power: 2 mW (+3 dBm)

8 bit ADC, 200kSPS (leftover component from last year)
- Normal Operation
10.5 mW, VDD = 3 V
- Automatic Power-Down
57.75 µW @ 1 kSPS, VDD = 3 V
Max Pwr Diss
17.5 mW

DAC
not selected yet

8051
We're having trouble finding power numbers for our 8051, but we'll keep looking

SST MELODY. We're not going to use this.
load capacitance x Vdd^2 x output switching frequency

MP3 encoder chips

This looks like more or less what we would want from a real-time MP3 encoder/decoder chip. However, I'm unable to find any further information about it on Analog Devices' website. I also can't find anything similar on Digikey.

In other news, we started actually working with our hardware a few days ago. Hopefully soon we can start testing out the XBee's capabilities.

An update: Kevin found this and this.

Purchasing boards

Just placed an order for a pair of breakout boards for the XBee modules, as well as breadboards.

4 x 2mm 10pin XBee Socket (SKU#: PRT-08272) = $5.00
2 x Breakout Board for XBee Module (SKU#: BOB-08276) = $5.90
2 x Basic Breadboard (SKU#: PRT-00112) = $23.90


Sub-Total: $34.80
Shipping & Handling: $8.62
Grand Total: $43.42

Total project cost so far is $112.48.

If we do 8 bit samples at 8 kHz, we'll need 64 kbit/s of bandwidth (not including overhead). At the max packet size, the overhead is 18 bytes per 100 bytes. This doesn't include the overhead of sending beacon packets and ack packets.

Purchasing 8051s, XBees

Thank you for your order!
Your total cost is $69.06 in U.S. currency, including $7.13 postage.

8051 ($7.74):
Digi-Key Part Number AT89C51RC2-3CSUM-ND
Manufacturer Part Number AT89C51RC2-3CSUM

Technical/Catalog Information	AT89C51RC2-3CSUM-ND
Standard Package	9
Category	Integrated Circuits (ICs)
Family	Microcontrollers
Vendor	Atmel
Program Memory Size	32K x 8
RAM Size	1.25K x 8
Number of I /O	32
Package / Case	40-DIP
Speed	60MHz
Controller Series	89C
Oscillator Type	External
Packaging	Tube
Program Memory Type	FLASH
EEPROM Size	-
Core Processor	8051
Data Converters	-
Core Size	8-Bit
Lead Free Status	Lead free
RoHS Status	RoHS compliant
Other Names	AT89C51RC2-3CSUM AT89C51RC2-3CSUM-ND

XBee Series 2, wire antenna ($21.00)
Digi-Key Part Number XB24-BWIT-004-ND
Manufacturer Part Number XB24-BWIT-004

Technical/Catalog Information	XB24-BWIT-004-ND
Standard Package	1
Category	Integrated Circuits, Modules, Units for RF and RFID
Family	RF Transmitter, Transceiver and Receiver ICs, Modules
Vendor	MaxStream Inc
RF Type	ZigBee
Package / Case	2.438cm x 2.761cm
Series	XBee™ Series 2
Frequency	2.4GHz
Features	2mW, 250kbps, Industrial Temp, Wire Antenna
Packaging	Bulk
Lead Free Status	Contains lead
RoHS Status	RoHS non-compliant
Other Names	XB24-BWIT-004 XB24-BWIT-004-ND

"The data rate for ZigBee technology is 250kbps (peak information rate 128kbps) compared to 720kbps for Bluetooth wireless technology."

More info

To Do

1. We need to calculate our bandwidth requirements and the amount of bandwidth we can actually get from Zigbee to see if this is feasible without compression.
2. Order 2 Xbee chips and 2 8051s and start playing with them.
3. Email the url of this page to Prof. Harris.
4. Look into audio compression algorithms to see if it's possible (and affordable) to encode in real time.
5. Think of other applications for Zigbee, in case streaming audio isn't realistic.


Getting surface mount components is a bad idea. We'll get DIP 8051s and use external ADCs and DACs. For now we can hold off buying ADCs and DACs, as that part of implementation should be trivial.

How Zigbee works:
Direct Sequence Spread Spectrum: Allows for multiple transmissions to share the same frequency range. Add a pseudonoise sequence to your signal, then subtract it at the receiving end. Your signal gets amplified, and all other signals get no gain.

Ad-Hoc On-demand Distance Vector: Establishes routes between nodes when needed. A node that needs a connection broadcasts its need. Other nodes forward the request. The route with the least hops is chosen and used.

CSMA/CA: Can't use collision detection with wireless because you can't transmit and receive at the same time. When a node wishes to transmit, it listens for a while to see if the channel is busy.

Unicast: A packet with just one target address.
Multicast: A packet with a range of target addresses.
Broadcast: A packet meant to absolutely be received by everyone. Each node that receives a broadcast packet makes sure to rebroadcast the packet three times. Broadcast packets are not good for general data, because the broadcast buffer is only of size 8, and broadcasts persist for 8 seconds.

Possible radio, 8051 choices

Today we looked at XBee modules. XBee, in case it wasn't mentioned in earlier posts, is MaxStream's implementation of a ZigBee radio. We decided on the XB24-BWIT-004-ND, which is an XBee Series 2 radio with a wire antenna. It costs $21. (XBee Series 2 implements ZigBee mesh, whereas Series 1 is apparently meant for other applications.)

As for microcontrollers: we wanted an 8051 with an integrated ADC and DAC, given our past difficulties with ADCs. Atmel has an 8051 variant with an ADC, DAC, and MP3 decoder, which sounds quite handy; unfortunately, they are BGA packaged. There are also no DIP 8051s with ADCs built in. In all likelihood we will probably have to do something like this.

How Zigbee does mesh

Keywords:
AODV (Ad-hoc On-demand Distance Vector routing)
direct-sequence spread spectrum

Carrier sense multiple access with collision avoidance

Maxstream XBee Series 2 manual:
http://maxstream.net/products/xbee-series-2/product-manual_XBee_Series2_OEM_RF-Modules_ZigBee.pdf