HUD based on JHD162 LCD  - need 32 mirrored  characters on this device displayed - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: August 03, 2016, 10:31:48 pm
content: Hello,I'm working on HUD and I'd like reflect in glass window this cheap JHD162 LCD with added I2C support using PCF8574T 8bit I/O extender to drive LCD using I2C.I know how to define custom characters on this JHD162 LCD hardware, but I'm not sure If by defining only 8 characters I could redfine whole ASCII table while display at low refresh frequency each defined character.I mean I need mirored 'A' so by creating its mirrored version I could later display this character; than I might need eg. digit 5, etc.... But this is 16 x 2 display so I need display 32 characters and only 8 seams to be able to redefine or maybe I miss something and I could for example define at 0x00 all needed custom 32 characters and diplay them one after another using the same address eg. 0x00?I don't need high refresh frequency and 10 Hz refresh could be fine or even 1Hz...Therehttp://www.tenettech.com/product/2442/16-x-2-character-lcd-display-with-backlight-jhd162a-greenthey wrote among others:QuoteReally, is it possible display 32 custom redefined characrers at the same refresh time on this JHD162 LCD ?As I said I need mirrored characters to be able see them mirrored by HUD window glass...

author: Buriedcode
author_rank: Super Contributor
timestamp: August 07, 2016, 12:25:16 am
content: I was going to reply to this earlier, but wasn't sure if I could be of any use.I don't think you can actively mirror characters on HD44780 based displays. You can add up to 8 custom characters however - which you provide the bitmaps for. Thats fine if there is only a maximum of 8 different characters displayed at any given time - you can very quickly repopulate the display buffer.If you have more than 8 different characters displays at any given time, then I would suggest a 132x32 graphic display as this is generally similar in physical size, and can display 22 x 4 characters (assuming you're using 5x7 standard characters, where there is a pixel space around each one making it 6x8, 132/6 = 22, 32/8 =4). These displays have no character ROM so you'll have to 'draw' the characters, but often have very simple controllers that make it a breeze to draw them, or any graphics you want.A third rather crude option is turn the module upsidedown and use another mirror so you have 2.

author: LeonV
author_rank: Contributor
timestamp: August 08, 2016, 05:10:01 am
content: I think i got a audio bar graph on an HD44780 once. Using each pixel column.From memory, some of the HD44780 models will let you do some tricky stuff where you can load a custom character into them, then display the character and that character will be in the display RAM, and wont get updated.Allowing you to load a new character into the same custom character RAM location, then telling the display to display that character.This may be per row, So you load 8 custom characters in, display the row,move the cursor, then load a new 8 character in, then display them in the lower row.I was able to get a much faster update rate out of it than what the pixels would update. So there may be other ways around you issue with just pooling it really fast.You should also be able to read the existing characters, let your code flip them, then re-upload the custom character to the RAM. That way you don't need to store the characters anywhere, and minimal code to flip them.

author: bktemp
author_rank: Super Contributor
timestamp: August 08, 2016, 05:54:04 am
content: Quote from: LeonV on August 08, 2016, 05:10:01 amFor a bar graph you need a maximum of 5 characters: 1-5 columns on + everything of. If you recalculate the custom characters only 2 are necessary: full on (bar) + partial on (last character)QuoteIf the controller can do it, it is not a 44780.If you write a CGRAM image and draw it on the screen and rewrite it, all previous drawn characters also get updated.QuoteReading the CGROM is not possible on 44780.A HD44780 can display only 8 user defined characters, so it is not possible to mirror the full display. Maybe there are some exotic variants allowing to flip the display image, but I would use a 122x32 GLCD. Some character LCDs use an ST7920. In addition to the 44780 compatibility mode it also supports a graphics mode.