Introduction.
A stand alone processor design often requires some means of communicating with a user other than a PC terminal. An LCD is an excellent choice as it is inexpensive, many alpha numeric characters may be displayed and the power dissipation is low. The down side is that it cannot be read from any appreciable distance.
An alternative is a display consisting of multiple 7-segment LEDs where the value of temperature or total number of events may be read from across a room. This kit is offered with either four 0.300 or 0.800 inch red displays for $13.00 or $15.00, respectively.
(This offering might be compared with an Applications Kit from Parallax for the Basic Stamp 2 which includes only a MAX7219 with no displays for twice the price. Another good reason for going with the Net Media BasicX BX24).
Kit Description.
This kit includes a MAX7219CNG (24-pin skinny Dip), four common cathode 7-segment LEDs, a schematic which complements the discussion of the MAX7219 on this web page and a supply of 22 AWG solid wire suitable for use with a solderless breadboard. Note that this is a kit suitable for assembly on a solderless breadboard and does not include a printed circuit board.
The MAX7219 uses three outputs from the BX24 to control up to eight 7-segment common cathode LEDs. Seven outputs from the MAX7219 control the segments of all 7-segment LEDs and thus are multipled to the same terminal on each of the displays. Eight digit outputs are available. Each digit output is connected to the common cathode side of one 7-segment display.
Segment current is controlled with a single resistor which is included in the kit. This approach obviates the necessity for 330 Ohm series limiting resistors.
The kit includes either four 0.300 or 0.800 inch red 7-segment LEDs.
The 0.300 inch display is a LSD3211-11 (MAN74) with a right
hand decimal point. The profile is a 14-pin DIP. Additional 0.3 inch displays may be purchased for $0.85 each.
The 0.800 inch display is a LSD8151-10 with a left hand decimal point. The pins are arranged as a 16-pin DIP with 0.6 inches between the two rows of terminals. Additional displays may be purchased for $1.25 each.
Documentation and Software.
A discussion of the use of the MAX7219 along with sample routines in zipped format appears on this web page. An additional discussion which uses the BX24's SPI port also appears on this web site. Three pages of schematics which complement these discussions are included with the kit.