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Site Alert


Site Alert Three ©
Warren Brown VK3BYD ©
April 2009
Project Overview
Site Alert is used to provide local site information from a remote UI-DIGI[A] APRS[B] Digipeater site via APRS Telemetry data.
The data is transmitted every 30 minutes and includes the average of four supply voltage readings, current in building temperature, number of PTT’s and the current mode of the Site Alert. The Parameter, Unit and Equation messages are sent once a day. (Further information on APRS Telemetry can be found in reference 1.)
Should the average voltage fall below a pre-programmed value Site Alert will turn off the Low Battery output until the average voltage reaches the upper pre-programmed value. This output can be used to control an external relay to remove power from the TNC and Radio. The battery alarm or the external alarm inputs will cause an APRS Item to the transmitted and an APRS Message sent
Site Alert uses an Atmel ATtiny2313 micro-controller, ADC0831 Analog to Digital converter, Dallas Semiconductor’s DS18S20 Temperature sensor and DS1307 Real Time Clock.
Feature Summary:
Software Version ‘FE’ (Dec 2008)
  • Eqns, Parm & Unit messages are sent at 0900 Site alert time (once a day)
  • All Alarm Message from Site Alert have messaging numbering
  • The Low Battery Alarm is only transmitted ~four times then Site Alert will “turn off” the Low Battery output.
  • An ‘OK’ message (only) will be sent when the voltage becomes high enough for Site Alert to “turn on” the Low Battery Output.
  • All the Alarm Messages and Alarm Items contain the last Voltage.
  • The Led will remain on whilst Site Alert is busy otherwise it flashes 9 second on/off.
  • Alarm input 1 has a lockout period of 9 minutes. That is once an alarm has been received on Input 1 no further alarms on that input will be recognised until after 9 minutes has passed.
Site Alert3 Plus will add the following features
  • Over Temperature alarming added to in built temperature sensor
  • Second A-D port with Low voltage alarming
  • Option for second temperature sensor with Over Temperature alarm
  •  Second relay output whose operation is selectable for an alarm on Input 1, an Over temperature on the main sensor , or a Low voltage on second A-D
  • A change in alarm status message is only sent four times. ( The Alarm Item is still sent until all alarms have cleared)
  • An enhanced user interface
Voltage readings will only be accurate for voltages above 8.1 Volts or below 19.9 (25.5 for SA3+) Volts.
Temperature readings are only accurate from 0 to + 85 Degrees C
Site Alert Local Commands must be correctly formatted, as there is NO checking for validity of the entries.
The Traffic counter will only count accurately to 511 in any 30-minute period.
Site Alert is not a full multi tasking device. However it is more than capable of coping with the day to day running of a remote radio site.
Sample Data
Do Not use this device for any application where human life is at risk or property damage may occur. The developer takes no responsibility wholly or implied for the use or performance of this product and offers no warranty of any type on this product.
Anybody who is interested in this project can contact me on e-mail at “vk3byd ‘at’” .
1)       APRS Protocol Reference Version 1.01

[A] UI-DIGI is copyright of Marco Savegnago IW3FQG
[B] APRS is copyright of Bob Bruninga WB4APR


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