Skip to main content
Topic: USB LCD BACKPACK (Read 71195 times) previous topic - next topic

USB LCD BACKPACK

I have been experimenting with the FT232R as a USB to SPI interface.  Some of it is on the web at www.chinwah-engineering.com

After looking at the BP LCD interface I got to thinking that driving the LCD directly with FT232R is a bad idea and that using the '595 simplifies the software immensely.  And so it follows that it would be possible to build a backpack for a LCD to run off of the USB bus.  Sort of like the Olimex PIC-MT-USB but without the PIC.  Should be a lot cheaper.

First pass at the schematic is attached.  The original was done in OrCAD so I made it into a pdf for the time being. 

Michael
"Too many projects, so little time"

Re: USB LCD BACKPACK

Reply #1
I wonder if it can also support the KD15xxx (sorry forget) graphical LCD, maybe on the other edge of the PCB.
Got a question? Please ask in the forum for the fastest answers.

Re: USB LCD BACKPACK

Reply #2
Shoot me a data sheet and I will check it out.
"Too many projects, so little time"


Re: USB LCD BACKPACK

Reply #4
No problem.  You will need two '595's because there are more signals to deal with.
"Too many projects, so little time"

Re: USB LCD BACKPACK

Reply #5
Great idea ... SURE electronics offers similar products based on a Prolific CP2102 USB UART and a PIC 16F722 ... the FT232R/HC595 design will be cheaper and more versatile ...

- 1602 LCD Display Board with USB (Edition I)
- 20*4LCD Display Board with UART Based USB(Edition I)
- 20*4 LCD Display Board with UART Based USB(Edition III)

I'd include 2 HC595's in the basic design and 3 headers for
- 2x8 pin 2 line header for HD44780 compatible 2x16/2x20/4x20 character LCDs
- 16-pin 1 line header for HD44780 compatible 2x16/2x20/4x20 character LCDs
- 20-pin 1 line header used for many 128x64 and 192x64 dot matrix LCDs

... maybe it's possible to use one 20-pin 1 line header for both the 16 pin character and 20 pin dot matrix LCD connectors.

Re: USB LCD BACKPACK

Reply #6
I looked a four different LCD displays.  The standard character LCD based on the HD44780 and three graphics displays.  Two graphics  displays from Sparkfun and one from Seeed.  I have attached a pdf spreadsheet of the results.  There is no common pinout.  All have eight data bits but range from three controls for the character display to five or six for the graphics displays.  All of the displays bring out both ends of the backlight LED's except the Seeed display only brings out the V+. 

I suggest that we have two connectors, one 1x16 pin for the character display and a 2x12 or 1x24 pin for the graphics displays. 

Two 74HCT595's, one for the data and the other for control.  The '595's will be in series so the SPI packet will be 16 bits.  All FT232R pins should be accessable. 

Backlight configureable to sink or source current.

Size of board should be the size and shape of a standard LCD character display.  1x16 pin connector should align with display connector.  Holes in corners for mounting on back of LCD display.

I will work on the schematic and bill of materials tonight.

Michael
"Too many projects, so little time"

Re: USB LCD BACKPACK

Reply #7
Here is the schematic and bom.  Yes I know they are pdf's.  I am so used to ORCAD it is hard to consider Eagle.  DesignSpark does look more capable.
"Too many projects, so little time"

Re: USB LCD BACKPACK

Reply #8
I really like your comparison charts. I recall that's why I didn't make a generic graphics LCD connector for the Bus Pirate. Three common graphics LCDs + universal HD44780 is enough that a pair of female-female jumper cables will connect to just about any display you care to hack.

Would you like us to capture the schematic in Eagle?
Got a question? Please ask in the forum for the fastest answers.

Re: USB LCD BACKPACK

Reply #9
I like the LCD interface comparison table (and the design). There seem to be quite a number of different interfaces for dot matrix (graphics) LCDs and there may be no way to find a solution that will work for all 128x64 and 192x64 displays - at least not without some extra logic (and jumpers) that would lead to a far more complex and expensive design.

However, for the HD44780 compatible character LCDs I suggest to add the 2x8 header (used on many wide displays (e.g. 20x2, 40x2) that's identical with the 16x1 header except for the pins with even numbers to be in one row and the pins with uneven numbers in the other row ... 

/EDIT/ OrCAD is my favourite schematics entry tool, too :) What about starting a KiCAD project ... KiCAD has an OrCAD interface ;)

Re: USB LCD BACKPACK

Reply #10
Sure, I forgot about that but I see them all the time.
Got a question? Please ask in the forum for the fastest answers.

Re: USB LCD BACKPACK

Reply #11
Why not break out all the signals to a header and let the user do the connecting? I think with 16 outputs you could interface [s:]all[/s:] most LCDs. Ana an other connector for power supply and backlight.

Re: USB LCD BACKPACK

Reply #12
@Sjaak: If the backpack board would be for experimenting only, one header for signals and an other one for power/backlight would certainly do ... however, if you want to use the board for some permanent/lasting project attaching the board to the LCD via headers would be better ... since the headers for HD44780 compatible character displays have a defacto standard, placing the 8x2 (J1B) header on one (short) side and a 16 pin header (J1A) on the (long) side would make the backpack board a general purpose board for character displays ... adding (a) header(s) for the data/control signals, power and backlight would allow to connect dot matrix (graphics) LCDs with wires as well while keeping the "direct header" option for the character displays (J3) ... MichaelZ thought of all this and more ... he added a full FT232R breakout header :)

I have one more suggestion that would lead to a minor change of the pinout of J4: By slightly reassigning the pins on J4 (and adding vias for a 5v/3.3V select jumper) the board would get the option of a Sparkfun FTDI Basic Breakout (5V and 3.3V) Board compatible header - allowing direct programming/communication of/with Arduino Pros and other designs that make use of this header.

Re: USB LCD BACKPACK

Reply #13
The revised pinout is good with me.  Do we want to add the TX and RX LEDs?  They dont have to be populated.

I will work on the getting the schematic into Eagle.  I have been able to import Eagle into DesignSpark PCB.  The one page limitation is a pain.  One page is too small for the DSP projects. :-)

Michael
"Too many projects, so little time"

Re: USB LCD BACKPACK

Reply #14
I just thought of something about the power.  The internal 3v3 regulator is only good for up to 50mA.  As long as we dont run the back light off of 3v3 we should be ok.

Michael
"Too many projects, so little time"