Roof-Link Circuit cont’d

Tue, 06 Mar 2007 16:43:16 +0000

What I’m trying to understand is how to make a slightly smarter circuit for the Roof-Link project (the mesh network of Xbee chips that send sensor readings from the 12th floor solar panel, down to our department on the 4th floor). What happens now, is that the 12th floor module senses the voltage coming in from the solar panel, and sends that information out through an xbee radio. This circuit is powered using the amps coming in from the solar panel, so once that drops down under 3.3V, no information is sent. I would like to be able to detect this drop down to 3.3V and have the Xbee send a series of zeros, stating that it is going to be sleeping (so instead of just null, get a few zeros before going null).

Another useful place for something like this would be the 8th floor module, which is currently used to pass data down from the 12th floor to the 4th floor. It is powered by a rechargeable battery pack. The Xbee radio chip is programmed to go into cyclic sleep, enabling maximum energy saving. It would be a good feature, to have the circuit detect the battery voltage going down, and having the xbee send out a signal before it dies, rather than just going silent.

For this reason, I’ve been playing around with the MAXIM 8212 voltage detector chip. Using the given solarbotics circuit. Doing a couple of tests to see which resistors (R2 and R3) I need in order to detect an input voltage level of 3.2-3.3. From the diagram in that pdf file, it seemed like R1=100k, R2 (trigger)=175K and R3 (hysterersis)=275K should do the trick. This triggers the load at a voltage of around 6V, and releases when it goes under 3.3V.

Now if I want the trigger to be around 3.5-3.7 (fresh battery) I need to place R2 = 200k. And to know that the battery’s power is ending (3.0-3.2 V), the hysterersis resistor value has to be R3 = 275k.

The 1381 IC is a voltage trigger. Using this IC in a circuit (I got the 1381S, which has a preset voltage trigger point at 4.0-4.3 V. I just wanted to try to make a simple BEAM circuit here, wakes up whenever it has enough voltage (4V in this case) to power the load. The 2N3904 is ***(goes ). Again here, I got a trigger from between 2.0 to 2.3V, half of what I’d expected.

Xbee setup for Solar Panel Network

Sun, 12 Nov 2006 17:35:29 +0000

Solar Panel Link:

Description of what our objective is…

Xbee Radios:

Addressing:

3 layers: Channel, Pan ID and DL/DH

Short 16-bit addresses. The module can be configured to use short 16-bit addresses as the
Source Address by setting (MY < 0xFFFE). Setting the DH parameter (DH = 0) will configure the
Destination Address to be a short 16-bit address (if DL < 0xFFFE). For two modules to communicate
using short addressing, the Destination Address of the transmitter module must match the
MY parameter of the receiver.

When an End Device associates to a Coordinator, its MY parameter is set to 0xFFFE to enable 64-
bit addressing. The 64-bit address of the module is stored as SH and SL parameters. To send a
packet to a specific module, the Destination Address (DL + DH) on one module must match the
Source Address (SL + SH) of the other.

AT commands:

+++ (no enter): places the chip in command mode
ATCN: exit command mode
ATWR: write configuration, so that the Xbee remembers the set parameters
ATBD: baud rate (ATBD3 – 9600 baud)
ATID: pan ID
ATDH: destination address (high)
ATDL: destination address (low)
ATMY: my address
ATSH: serial number (high) – this is a unique address
ATSL: serial number (low) – this is a unique address
ATDB: signal strength of the last RF packet received
ATPL: Power Level (default: 18dBm on the Xbee pros)
ATIR: Set sample time (ATIR0×0A – samples every 10ms)

Modes of operation:

Xbee I/O Commands:
IA (I/O Input Address) Command
The IA command
is used to bind a module output to a specific
address. Outputs will only change if received
from this address. The IA command can be used
to set/read both 16 and 64-bit addresses.
Setting all bytes to 0xFF will not allow the reception
of any I/O packet to change outputs. Setting
the IA address to 0xFFFF will cause the module to
accept all I/O packets.

PR – The PR command is used to
set and read the bit field that is used to configure
internal the pull-up resistor status for I/O lines.
â€œ1â€ specifies the pull-up resistor is enabled. â€œ0â€
specifies no pull up.

bit 0 – AD4/DIO4 (pin 11)
bit 1 – AD3/DIO3 (pin 17)
bit 2 – AD2/DIO2 (pin 18)
bit 3 – AD1/DIO1 (pin 19)
bit 4 – AD0/DIO0 (pin 20)
bit 5 – AD6/DIO6 (pin 16)
bit 6 – DI8 (pin 9)
bit 7 – DIN/CONFIG (pin 3)
For example: Sending the command â€œATPR 6Fâ€ will turn bits 0, 1, 2, 3, 5 and 6 ON; and bits 4 & 7
will be turned OFF. (The binary equivalent of â€œ0×6Fâ€ is â€œ01101111â€. Note that â€˜bit 0â€™ is the last digit
in the bitfield.

Analog I/O commands support page

Complete Xbee Manual

Xbee Support Page Link

Giladon-line » xbee

Roof-Link Circuit cont’d

Xbee setup for Solar Panel Network