LCD display - Page 1
Forum section: electronics / projects

author: electronics man
author_rank: Frequent Contributor
timestamp: February 13, 2014, 06:36:55 pm
content: Im looking for a display that i can controll the position of a pixle using analog voltages like am oscilloscope in xy mode. does anyone know of any

author: apelly
author_rank: Unknown
timestamp: February 13, 2014, 07:09:11 pm
content: Not analog, but it should be simple enough with an ADC and a small ?C. Even I could do it.

author: mariush
author_rank: Super Contributor
timestamp: February 13, 2014, 07:15:30 pm
content: There are some that allow composite or vga input but they're expensive.What you could do would be to use a PIC32 or maybe even a beefier PIC18 to take in vga input or svideo/composite and buffer it and translate it to a regular lcd screen.For example this one supports both serial in and separate hsync + r,g,b etc so it's easy to control using a microcontroller provided it's fast enough:http://www.digikey.com/product-detail/en/T-55343GD035JU-LW-ADN/73-1335-ND/1969141Or something like this, cheaper but a tiny bit harder to connect and drive using a mcu (screen is split into 2 areas each with the separate driver in the back of display):http://www.digikey.com/product-detail/en/NHD-2.4-240320SF-CTXI%23-1/NHD-2.4-240320SF-CTXI%23-1-ND/2626410

author: electronics man
author_rank: Frequent Contributor
timestamp: February 13, 2014, 07:22:35 pm
content: Quote from: mariush on February 13, 2014, 07:15:30 pmcould i do it whith an arduino

author: electronics man
author_rank: Frequent Contributor
timestamp: February 13, 2014, 07:50:42 pm
content: oh yeah i forgot to mension that it needs to work fairly fast

author: mariush
author_rank: Super Contributor
timestamp: February 13, 2014, 08:08:45 pm
content: Quote from: electronics man on February 13, 2014, 07:22:35 pmNo. It's too slow.Here's for example a pic32 and three ad converters and other parts taking vga input and converting it to a small lcd :He uses external adc for each color because it's faster this way and the three converters can run in parallel, so the pic doesn't have to wait for data.A pic32 running at 80 Mhz can generate 800x600 vga (actual display 400x300) at 60 fps so if it can do this, it should have the speed to send data to a lcd display:But how fast the actual lcd will work, it depends on how it's manufactured, what drivers that lcd is using and so on. It may only update 3-4 times a second, it may update 25 times a second, 60 times a second.. you have to read the datasheet of the lcd display you choose.You can probably do 320x240 with a PIC running at 32-40 Mhz.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 13, 2014, 09:00:50 pm
content: all i want to do is build a little osilloscope and i just want to controll the horizontal whith at ramp and have a signal on the vertical i dont mind if it is a module or kit

author: mariush
author_rank: Super Contributor
timestamp: February 13, 2014, 09:55:18 pm
content: And how do you want to tell the display to draw each pixel?. You need some logic to convert that x and y to pixels turned on and off ...A lcd display is dumb, it's basically a matrix of dots, it takes a stream of bytes, 3 for each pixel (red,green,blue) and changes the color acordingly. Some lcd displays have drivers which support instructions like lightning up a single pixel, drawing lines and so on, combined with the dumb mode of just dumping whole rows of pixels informationA video card with a vga sends to a lcd display row after row of pixels (an analogue voltage for each color represents the intensity of that color) until the total number of rows is sent, 60 (or whatever the Hz frequency) times a second.A lcd display like the ones above can accept data in the same way but somewhat more microcontroller friendly... send 320 sets of 3 bytes (red, green, blue) for each row on the screen. Do this 240 times and you have a 320x240 screen filled with info.The framerate will depend on how fast the microcontroller sends all this information and how fast the drivers on the back of the LCD can take in that information and set the pixels to the right values.For example ... 320x240x3 bytes = 230400 bytes or 1843200 bits or about 1.8 megabits , for one frame. The higher the microcontroller frequency, the faster it can push those 1.8 megabits to the lcd display.. ex a pic32 at 80mhz can probably do about 18-20 megabits per secondSome LCD displays like the Newhaven one are just 262.400 color displays so each pixel is represented by 16 bits (5:6:5 bits for each color usually) so it's even faster, needing 320x240x2 = 153600 bytes/s or about 1.2 megabits. The lcd drivers used also allows you to move to a particular position and start dumping pixels from that point, so it's possible to get high framerates by just drawing some small areas of the display instead of repainting the whole screen.Of course, you don't always have to fill the whole screen, so if your microcontroller or whatever you use is smart enough to send the lcd display just the differences you may get faster updates.

author: PaulAm
author_rank: Frequent Contributor
timestamp: February 13, 2014, 10:08:35 pm
content: What you're looking for most likely doesn't exist as an off-the-shelf item.You can build what you want with an Arduino hooked up to an LCD graphics screen. Use 2 of the analog inputs as X and Y and write a program to translate the values to coordinates on the screen. Lot of details left for individual study (how long to leave a pixel turned on?, scan rate, memory, etc).LCD screens are digital devices, you have an analog signal, you need something to bridge the two worlds.You can probably do something like that for $50 US.Don't exceed 5V on the input, it won't be fast, but you could probably get 50 KHz bandwidth, maybe. Could be lots worse.

author: dannyf
author_rank: Super Contributor
timestamp: February 13, 2014, 10:39:37 pm
content: QuoteLook into 1980's TV game consoles - they take (analog) joysticks. All you need to do is to sample your signal and output an analog signal in place of the joysticks.

author: andrewfernie
author_rank: Newbie
timestamp: February 14, 2014, 02:40:24 am
content: Google "hp xy display". You will find a number of models. Not sure if any of them are made these days, but there is always eBay. Deflection speeds can be slow, so check the model you are interested in.