tim_board

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TIM BOARD

TIM BOARD FOR APRS

Une firme en Argentine fournit une carte d'acquisition de télémétrie compatible APRS. Cette carte reçoit une entrée GPS au format NMEA0183, et un certain nombre d'entrées analogiques ou digitales. Voici un texte de présentation en anglais et une vue de cette carte en attendant d'avoir une description plus complète. Le logiciel de configuration serait très intéressant à observer, le seul point négatif est la résolution de la conversion analogique digitale qui n'est que de 8 bits. Mais s'il s'agit de traiter des données météo classiques la précision pourrait être acceptable.

Le codage se fait entre 0 et 255, pour une tension de 5 volts chaque bit représente une tension de 5 / 255 = 0,0196 volt.

Dans le cas d'une résolution de 12 bits, on aurait un codage entre 0 et 4095, donc une tension par bit de 5/4095 = 0,00122 volt. Le rapport est pratiquement de 16.

texte de présentation original en anglais :

The TIM board is an APRS compatible, packet radio telemetry unit. When attached to a transmitter, the unit sends GPS position reports, telemetry data, a beacon text message and CW ID at user-selectable time intervals. It is capable of sending these messages via a digipeater path with a maximum of eight hops. The units accepts GPS data in NMEA 0183 format for position reporting. Can report five A/D inputs ( 8 bits resolution ) and eight bits of digital input too. The following text is an example of packet frames :

NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
T#000,039,035,033,028,025,11111111,TIM v1.1
NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
T#001,056,050,044,041,036,11111111,TIM v1.1
NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
$GPGGA,141811,3444.891,S,05822.408,W,1,7,001.1,12,M,015,M,,/GPS ON
NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
T#002,050,045,038,034,030,11111111,TIM v1.1
NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
T#003,057,048,045,042,035,11111111, TIM v1.1
NOCALL/APRS/WIDE2-2>APRTLM>UI,C,f0:
$GPGGA,141911,3444.890,S,05822.409,W,1,7,001.1,14,M,015,M,,/GPS ON

Through Windows 98/ME/2000/XP configuration software, the user is able to customize callsigns and other parameters. An on-board memory stores configuration information indefinitely and configuration software can be run as often as needed to change settings. The on-board voltage regulator accepts power from an unregulated 7-30 VDC source. The TIM board provides 5 analog-to-digital inputs. The reference voltages for these inputs are the +5 VDC supply voltage (+5) and GND, which are digitized to 255 and 0 respectively (i.e, 8- bit resolution). Eight TTL digital inputs telemetry bits are provided. The TIM board interfaces to one's transmitter through the connections MIC GND, PTT and RXA. Prior to transmitting, RXA is sampled. This is important for collision avoidance on the chanel.

Once the communications channel is clear, the Push-To-Talk signal PTT is actived ( low or high, as selected in software ) to key the transmitter, ( PTT led will turn on/off as selected in sofware too ), and transmission is complete, PTT is deactived. The single-turn potentiometer set the signal level audio output.

Serial communications with the TIM module are required for configuring the device with the user's callsign and other information and also for receiving data from GPS receiver, if attached. Ideal for Car, Airplane, Balloon, Rocket ou Sat telemetry project.

the TIM board

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