More MultiDisplay Information
Schematics and Pictorials
Major Features :
Pelorus : 36 LEDs, 4 yellow LEDs at cardinal headings
Numeric : 3 display digits, 0.36 inch character height
DF Input : RS232 Agrello DF message
baud rates 1200 to 9600, strap selectable
Data checks : Old data ( 3 seconds ) is abandoned or blinked
Range checking for DF bearing ( 000 to 359 )
DC Power : 7 – 14 VDC
Micros : Microchip PIC 16C773 micro, for pelorus display
Microchip PIC 16F84 micro, for numeric display
Schematics and Pictorials :
Download links to schematic diagrams and technical details for the MultiDisplay are provided here. For additional information about the MultiDisplay board, inquire directly by e-mail.MultiDisplay pelorus schematic ( 15 Kb GIF file )
General Description :
The MultiDisplay board is a combination pelorus / numeric DF display for use with the PicoDopp DF, or other DFs that generate Agrello format RS232 messages. It uses 36 LEDs for the pelorus display, ( 10 degree resolution ) with 4 yellow LEDs at the cardinal headings. ( N / E / S / W ) The numeric display uses three 7-segment LED readouts with character heights of 0.36 inches.
The MultiDisplay board offers ( strap selectable ) baud rates ( 1200 to 9600 ) for the RS232 input, and alternative display modes ( strap selectable ) for invalid / old DF data. ( 3 seconds of "dwell" time for DF data ) For the pelorus, the display can "hold / blink" the last valid DF message, or it can abandon the data and "orbit" the display. For the numeric readout, the display can hold / blink the last valid DF data, or it can abandon the data and blank the display. ( display "dashes" )
For enhanced nighttime viewing of the pelorus, the entire pelorus display is briefly "flashed" about once per second, to provide a circular "context" for interpreting the DF-selected LED. The pelorus display is updated about 15 times per second, the numeric display is updated about 3 times per second. Power is +7 to 12 VDC. A power-on self-test ( sequentially ) illuminates all LEDs for about 3 seconds.
PicoDopp Connections :
The figure below shows the connections for the MultiDisplay. A more detailed diagram is provided in the section called COMPLETION INFO. Additional connections for the optional local displays are provided in the website pages for those displays
Technical Description :
The MultiDisplay board employs 2 microcomputers to achieve virtually all internal functions. A PIC 16C773 is employed to drive the pelorus display, and a PIC 16F84 is employed to drive the numeric display. Code for the micros is written in PIC assembly language, and is available on request. It is worthwhile to point out ( to hardcore PIC hackers ) that this board is suitable as a general-purpose azimuth display board, for other non-DF applications ( such as a compass or GPS waypoint display ) with suitable code changes.
The pelorus display uses 36 LEDs arranged in a 6 X 6 matrix. The pelorus LEDs are directly driven by the outputs from the 16C773 micro, through current limiting resistors. The numeric display consists of 3 common-anode readout digits that are multiplexed ( "scanned" ) by the 16F84 micro. The numeric readouts require more current than the micro can directly deliver, so buffer transistors are employed, ( 3 PNP for the anodes, 7 NPN for the cathodes ) with current limiting resistors. An onboard 5V power regulator ( 7805 ) allows operation from 7 to 14 VDC.
RS232 bearing data is received by the UART in the 16C773 micro, with an external NPN transistor employed to invert the message polarity, prior to the UART input. The RS232 input impedance is 10K ohms, so it can be tied in parallel with other devices on the PicoDopp RS232 output , without causing interference. Bearing data is transferred to the 16F84 micro ( from the 16C773 ) by means of a pulse train, enabled by a separate ( control ) line from the 16C773. Each pulse train contains 0 to 360 pulses, with 0 pulses indicating invalid / old DF data.
In addition to all the other functions, the 16C773 does some error and range checking on received data, for each message received. If the data is not numeric, or if the data’s numeric value lies outside the range of 000 to 359, the data is declared invalid.
The RS232 input message is received about 15 times per second, ( if available ) and must comply with the ( very popular ) Agrello DF message format, as shown below :
Agrello DF message format :
Where % = message start character
BBB = signal bearing degrees ( 000-359 )
Q = signal quality ( 0-9 ) ( fixed @ 7 in this design )
<cr> = carriage return