Direct PC Serial Port connection to LED Display Driver

[lightspeeed]

serial port led

Hi all,

Does anyone here have any experience hooking up a Maxim MAX7219 Serial Interface LED Display Driver directly to a PC serial port?

I am trying to do a simple Visual Basic application that would write directly to the PC serial port, which in turn, drives the MAX7219 to display stuff on a custom LED matrix.

I know most times these LED drivers are used in conjuction with microcontrollers for standalone operation. But my application will have the PC next to it at all times for other reasons, so I may as well use the built-in I/O of the PC (I'm thinking of virtual serial ports via USB).

I'm also aware that Maxim has published an application note that shows an implementation of the MAX7219/7221 where it directly talks to a PC parallel port to simulate serial activity.

The mystery to me here is that after quite a bit of searching, I still havent found anyone out there who has done a direct serial connection.

Please pardon me, Im not an electronics engineer, so if this is a stupid question - I'm sorry, in advance (I just need to be told that it is).

So, is there anything fundamentally and technically wrong about hooking the display driver as mentioned?

Thanks for any help!

 

[lambtron]

display connection between serial port and led

The MAX7219 has an SPI (aka "Serial Peripheral Interface") bus, which is incompatible with the serial RS-232 port on a pc. Some of the key differences between these two interfaces:

Clock. An SPI interface requires separate clock and data signals but the pc's serial port has only the data signals, so there is no clock signal available from the pc to drive the SCK input on the MAX7219.

Signal levels. SPI signal levels are not compatible with the RS-232 signal levels found on the pc's serial interface. SPI uses standard logic levels (e.g., 0-5V) whereas RS-232 levels are bipolar.

Protocol. The pc's serial protocol includes start and stop bits to frame the data, whereas the SPI protocol employs a chip select signal for this purpose.

 

[lightspeeed]

vb.net rs232 led display

That was quite enlightening... Many thanks, Lambtron!

 

[IanP]

led matrix connect to serial port

One option is to use simple microcontroller such as PICAXE-08 (8-pin), connect it directly to the RS-232 port and program its general purpose I/O pins to control MAX7219 through it's SPI ..

After all, to connect 0-5V device to the PC's serial port you would use an RS-232 driver IC, something like MAX232, or smilar, but PICAXE-08 already does that job, so no additional ICs are required ..

Regards,
IanP