320 x 240 Grpahic Display for $4

[bobledoux]

Electronic Goldmine (goldmine-elec-products.com) has a large 4.75 inch graphic display (G18246) for $4.00 I believe it is this model. I've attached a pdf from the manufacturer. Note: It appears to require an external driver. The LC79430 and LC79401 chips have data sheets on the web.

 

[Sceadwian]

It includes the drivers, which are the LC79430/79401 chips you mentioned, they're barely called drivers as it's nothing more than a massive shift register array, but it makes interfacing with a micro controller trivial, you just have to feed it a bit stream.

 

[bobledoux]

The LC79430 and LC79401 are often driven by a controller, like the Epson 1330 to reduce off-board workload. I know this board includes four, LC79401's and three, LC79430's. I have seen boards similar to this one, that have traces for, but do not include the 1330. Does anyone know what the back of this board looks like? Does it have an additional controller and perhaps RAM or negative voltage power source?

 

[Sceadwian]

I can find links to the LCD drivers, not anything useful for the Epson 1330, what are you talking about? Please provide reference to this type of display being used with an on board controller.

The schematic/pinout that you've linked is a serial interface to a large shift register array, there is nothing so far no indication that a driver for higher functions exists.

 

[Blueteeth]

Haven't checked the display but seems like its controllerless. The SED1330 is somewhat limited, often used for that displays' slighter smaller cousins. The SED1335(F) was popular as an onboard or external controller which has been replaced by the S1D13700 (internal ram, lower power etc..).

Sceadwian: I believe in general the term 'driver' in the context of LCD's refers to the pixel drivers, which are indeed just giant shift registers that work on positive and negative voltage, and the term 'controllers' are used for higher functions such as refreshing, addressing, text generation, window-in-window, cursors etc.. I said 'in general' because the two are often interchangable and have caused me headaches in the past when researching how to drive these things.

Alas, my 'weakness' is LCD displays and I've collected a good ~40 graphic ones over the years many without controllers, and although the idea of a large monochrome LCD for $4 is appealing, its a fair bit of work just building a controller, as the S1D13700's tend to go for $10. Along with a -VEE circuit, and a CCFL inverter for the backlight, it generally adds up to a fair ammount of money, not to mention the time/effort to build the external cotroller board - believe me I've wasted a lot of time doing it with Epson controllers, CPLD's, and FPGA's. There have been a couple of old AVR projects which drive (sorry, control ) these displays directly using external SRAM but given the speed they don't have much in the way of 'options'.

I'll admit $4 is great for such a display, but it can be a real hassle to get them into a project, to the point where the price doesn't really mean much. If the OP, or anyone reading this thread is savy with programmable logic I can post a basic CPLD controller that'll handle refreshing and addressing, leaving the main micro only having to draw pixels/text.

 

[bobledoux]

The $4 Display

Hi again, Blueteeth.

When I was talking about a "controller," I was thinking of a chip to handle fonts and graphic placement. Its true the $4 LCD is capable of being driven without an intermediate controller, but that means all graphics must be handled outside the LCD.

I recently developed an instrument package for one of my hot air balloons using a 64 x 128 pixel display with KS107 and KS108 controllers. A PIC 16F690 provided all data input and display format. It took about 4000 lines of code in assembler, much of which consisted of graphics and fonts data tables.

The display calculated and displayed, altitude,elapsed time, balloon temperature and rate of climb as a bar chart. I've attached a copy of the display.

The PIC was only running at 4mhz and had no difficulty updating the display every half second. So I know it can be done for slowly changing data.

 

[Blueteeth]

Hi, the KS0107 and KS0108 chipset are both drivers and controllers in one, they have the IO's and shift registers to control each pixel - but also the field memory (RAM) to refresh the display. So whilst any micro attached to these has to 'draw' text, essentially the LCD has an inbuilt controller - albeit with limited functionality. It stores the bitmap in memory, and constantly refreshes the display without intervention from whatever is controlling it. Draw a pixel at one address location - and it'll stay there. The micro controlling it treats the LCD is memory, writing to address locations.

The larger LCD you posted has no such controller. It requires clock and data lines to 'scan' across the display and refresh the image frame from memory. Much like a raster scan on a TV. That is pretty much the main purpose of an LCD controller - character generation, cursors, and scrolling/rotation are just handy extra's. So, clocking in data across a line, then moving to next line before flying back to the top, if you draw a pixel in one location, unless you draw it again on every frame, it fades, so it require constant refreshing, usually at around 60-80Hz. Doing this with a microcontroller, a few numbers to show it *is* possible, but no-where near as straight foward as dealing with the KS108.

320 x 240. 4-bit interface (writing to 4 pixels at a time). Refresh rate 70Hz.

320 horizontal pixels /4 = 80 writes per line. Often some delay is required before a 'end of line' sync pulse, so say this is 82.
240 lines - again, some 'dummy' lines are added as a delay, so call it 244 lines.

number of writes per second = frame rate * lines * writes per line = 70 * 244 * 82 = 1400560. So you'll need to provide a new 4-bit nibble at 1.4MHz. Given that data must be read from a memory (internal or external) you can see that it'll take a good 4 cycles per 4-bit write. So, even without drawing anything on screen, printing fonts, your micro will be too busy just taking data from memory, and sending it to the display. Fast micro's, like AVR's (20MIPS) and perhaps the PIC18F series might be able to do this.

Also, memory, 320x240 is 40bytes 240 = 9600bytes = ~9.4Kbytes.

It is such a mundane task, moving data, doesn't require intelligence, just counters, but at a speed beyond that of most 8-bit devices. And it seems like a waste to have all the goodies of a fast PIC or AVR just to read from ram and send to a port.

Sorry for the pesimistic 'numbers' post. I'm not trying to discourage folk from using the display, 320x240's are awesome! (smaller pixels, finer detail, lots of text and cool symbols) just that without a dedicated controller IC, or perhaps programmable logic (just counters and memory really) it can be very difficult to drive.

All that said, despite the cost of a controller IC, they don't actually require much in the way of external circuitry. SRAM (usually 256k, 32k x 8, very cheap and common) a crystal oscillator, and thats pretty much it. The VEE LCD drive voltage for 320x240's is usually around -22V @ ~2mA (usually negative, sometimes positive!) which can also be a source of headaches. The 128x64 displays which only require -8V often have this DC-DC converter built in as cascaded ICL7660's.

Again, sorry for the long post, I got a bit obsessed with LCD's back in the days of sticking them on ones PC to display pointless information and my mind is stil full of crap about em

Edit: nice scale on that LCD! Even graphic LCD's with controllers can be a ***** to drive, but the ability to address individual pixels makes them so versatile for displaying information in different ways I tend to use the 128x64's over character LCD's these days. Bargraphs, custom fonts, always makes projects/prototypes look sweeet!

 

[bobledoux]

Thanks for the clarification.

I wanted to see a photo of the back because I think the traces are there for a controller and RAM. The EW34F50 on this page may be the unit:

**broken link removed**

 

[Blueteeth]

Thanks for the clarification.

I wanted to see a photo of the back because I think the traces are there for a controller and RAM. The EW34F50 on this page may be the unit:

**broken link removed**

That is often the case! meaning one doesn't require an external PCB, just solder on the pads unpopulated on the LCD board. If the negative voltage generating circuit is also on the board, that could prove troublesome as they are many ways to do this and would require the same parts (for the same layout) as the board was deisgned for. But the controller pinouts would most likely be an SED1335, and 28-pin SRAM always has a standard pinout.

From the part number, I came up with this:
**broken link removed**

It is difficult to know whether or not there are landings for a controller, only a few contorllerless LCD's I have have these pads, most just have the drivers with but some non-populated area's for -VEE circuit.

Could just order one anyway and post a pic I'm sure others would be interested

 

[bobledoux]

I have other projects on my list right now so I'll leave this LCD on hold. There may be too much effort needed to get it going.