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Forum Index : Microcontroller and PC projects : Picomite - Save/Capture image 
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Upweywarrior Newbie  Joined: 22/07/2022 Location: United KingdomPosts: 3 |
Hello all, So i am looking to screenshot the Graph that Plots my sensor inputs On my PicoMite. I have a Wav Share 3.5" Eval display hooked up. I tried to use; SAVE IMAGE filename$ [, StartX, StartY] I was unsuccessful using this and was thrown an error After consulting the manual again I discovered that I would need an ILI9341 based LCD screen to use this command. I however, have a ILI9488/XPT2046 Display  So my question now is, Is there an Easy way to capture a screenshot whilst using a different display? My logic tells me i could probably iterate through the pixels individually & log/read there colour value, Then store and format this data into the Structure required for that format. In this case a .BMP image. I found this command; PIXEL( x, y [,page_number]) REM - Returns the colour of a pixel on an LCD display. According to the manual This should be compatible with my display. So now Im looking for information regarding .BMP file structure/formatting, and advice on writing this captured img data to the SD card. Any advice or reading material That could help me resolve this predicament would be much appreciated. Thanks Robert |
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 9110 |
Save image works on the ILI9488 IFF you connect the display's MISO pin using a 680 ohm resistor |
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| Upweywarrior Newbie Joined: 22/07/2022 Location: United KingdomPosts: 3 |
Brilliant, So It just needed extra resistance on GP12 between the two boards? Like so. When I'm home later I will give this a go, could you explain in any more detail as to why this is the case? Does the pi see the added resistance and think its a different display perhaps? just curious Thanks Robert. |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6780 |
The MISO pin on the ILI9488 doesn't tri-state properly - it's a fault on the display. If anything else shares that pin then the display will prevent it from working. Using a resistor lets other devices use the pin. 680R is just a value that was found to work. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6097 |
To get the data from the display, you need the data line that goes from display to controller connected. Without that, you can only send data TO the display. Why they put out display modules without both data lines is anyone's guess. Jim VK7JH MMedit MMBasic Help |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
"Why they put out display modules without both data lines is anyone's guess." The ILI9488 controller chip MISO output is defective, unable to go tri-state preventing use of touch and SD on the same SPI. On some displays WaveShare have left that pin disconnected. Touch and SD can however cope with a 680R load so it is possible to make it work, provided there is a track from the ILI9488 chip to the header pin. |
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vegipete Guru Joined: 29/01/2013 Location: CanadaPosts: 1109 |
Your program generates the plots, so your program can also decide how to save the data that generated the plots. Then a companion program, perhaps running on MMB4W, can read that data and generate a new, copy-able plot. Or write a data file that can be fed into Excel for graphing. Visit Vegipete's *Mite Library for cool programs. |
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| Upweywarrior Newbie Joined: 22/07/2022 Location: United KingdomPosts: 3 |
Thanks for your help so far, Here are some more details for my display. Option SPI GP10,GP11,GP12 Option Touch GP16,GP17 Option SDCARD GP22,GP5,GP18,GP19 Option LCDPanel ILI9488w, Rlandscape, GP8,GP15,GP9,GP13 Under the Display documents it says "Controller: ILI9488/XPT2046" Display Documents My option for LCDpanel is ILI9488W because i am using the Waveshare 3.5" eval board) According to the manual, Both The ILI9488W & ILI9488 Initialises a TFT display using the ILI9488 controller. Could anyone explain the difference between the two and is it possible to use the 680R Mod/Fix with my display If i was to change my option settings to; Option LCDPanel ILI9488, Rlandscape, GP8,GP15,GP9,GP13 (removed the "W") And then added a 680R in series on my MISO line(GP12), Would this Fix The "Get colour of Pixel" command & the "Save image" command errors? Sorry for all the questions, I'm still learning. Thanks Robert. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6780 |
MISO is a signal from the display to the Pico. It's needed to read data back from the display. The MISO pin on the ILI9488W works as intended, so the series resistor isn't needed. It's the MISO pin on the ILI9488 that is faulty. That signal comes from the ILI9488 chip, so it appears that there is a faulty production run. I'm assuming that there must be a difference in the configuration routines, otherwise there would only be one driver. :) It may be checking for a MISO signal) Note that if nothing else is connected to the MISO pin (Touch data or a SD card for example) then the 680R resistor isn't needed for either display. It's just that the ILI9488 won't tri-state the pin to let another device use it. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9110 |
WRONG. The 3.5" Waveshare ILI9488 is wired parallel with external shift registers and there is absolutely no way to read the framebuffer. Therefore BLIT, the PIXEL function and SAVE IMAGE can't work on this display. The displays which work are ILI9341, ILI9481 (with 680ohm resistor - NB: type in my post above), ST7789_320 and all the mono and SSD1963 displays Edited 2022-07-24 01:57 by matherp |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6780 |
That should perhaps be made a little clearer in the manual, Peter. When comparing the ILI9488 and ILI9488W there it is only indicated that the ILI9488 has a MISO problem. Perhaps the section should start with a statement that only a few, indicated, displays can be read by the PicoMite. Edited 2022-07-24 02:12 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| DaveJacko Regular Member  Joined: 25/07/2019 Location: United KingdomPosts: 76 |
Have a look at GFXterm by our very own Robert Rozee. This simple program allows a Micromite, Picomite, (or anything with RS232) to plot directly to the PC screen, where it can be screenshotted if needed. and it's a nice terminal for programming too. BTW, upwey, project sounds interesting, can you tell us more? |
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| LewW Newbie Joined: 16/01/2018 Location: AustraliaPosts: 15 |
Hi all, I'm really interested in using SAVE IMAGE with the Picomite backpack, and I'm currently using the ILI9488 display. If I understand correctly (i.e., assuming that Matherp's "type" in his second post was meant to be "typo"), SAVE IMAGE will not work with the ILI9488 displays even with the MISO pin connected or connected via 680 Ohms). Is that right? Also, if I understand correctly, SAVE IMAGE will work with the ILI9481 display if the MISO pin is connected via 680 Ohms. Is that right? Are there any disadvantages in using an ILI9481 display instead of an ILI9488 display with the Picomite backpack? I will be grateful for any clarification. Lew. PS I know that connecting the MISO pin with the ILI9488 will compromise the Touch function, but I would only connect it when I want to save an image. I could live with that! |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
The 680Ω trick is unreliable if touch and SD card are also connected to MISO on the Pico. A better method for a 3.5" TFT ILI8488 is a 1N5819 or 1N4004 diode connected from LCD_SDO to Pico MISO and a 1.8kΩ to 10kΩ resistor from LCD_CS to MISO. This allows touch and SD card to work properly. Scroll down in this thread For a 4" IPS ILI8488 the resistor must be 1.8k as there is a 4.7k pullup on SD_DO. Also the 4" IPS panel must only be supplied with 3.3V as the voltage regulator isn't installed. You can test if the screen is being read properly with this:- > clear : dim a$(2)=(" Blues"," Greens"," Reds") : dim integer b, c, n the code window has broken the second line, it needs to be one line.> for b=0 to 2:n=0:for c=0 to 255:pixel 9,9,c<<b*8:if pixel(9,9)=c<<b*8 then:inc n:endif:next:?n;a$(b):next 64 Blues 64 Greens 64 Reds for b=0 to 2:n=0:for c=0 to 255:pixel 9,9,c<<b*8:if pixel(9,9)=c<<b*8 then:inc n:endif:next:?n;a$(b):next Edited 2024-08-17 12:39 by phil99 |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6780 |
The ILI9481 can be regarded as the "standard" LCD TFT display. Everything works properly on it. The ILI9488 has a silicon bug. Normally, if MISO is connected like a ILI9481, the touch controller attempts to send data at the same time as the display, so the advice used to be to leave MISO disconnected. That prevented the data clash but also meant that you couldn't read data back from the LCD. The current hacks with a resistors and sometimes a diode are attempts to get round the problem. The 680R resistor simply current limits MISO so that the clash doesn't matter. The resistor/diode form a gate. Ultimately though, the ILI9488 has been faulty from the start and almost certainly won't get fixed. It's not the ideal choice for a display. There is also a ILI9488W. This isn't a ILI9488, it is write-only. It is always impossible to read from this display. . Edited 2024-08-17 17:42 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
If you already have the ILI9488 it isn't hard to make it work properly. To avoid modifying your PCB the diode and resistor can be added to the top of the header on the ILI8488. As T_DO connects to Pico MISO connect the diode anode to LCD_SDO and cathode to T_DO and the resistor from LCD_CS to T_DO. If the PCB has a track from MISO to LCD_SDO snip the SDO pin off the display header. |
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