Guru
Joined: 11/02/2018
Location: AustraliaPosts: 2247
| Posted: 05:59am 21 Nov 2022 |
Decided to see if the BC557 could be made it work reliably. The closest I have is a BC558 and it too needed a very low value base resistor. As the chip problem is that SDO is active low when it should be off a diode with anode to SDO was added as per the diagram. Tested with Pixel (above colour counters return 64 each for R, G & B), Blit, Files, Load Image and Save Image.
Using the "Remove Bits Till it Fails" design philosophy the Diode Switch passed all the above tests with just one diode.
PS Touch also works.
Edited 2022-11-21 22:10 by phil99
Footnote added 2024-04-15 12:11 by phil99
The 4" IPS ILI9488 is different to the panel above. The resistors near the SD socket are 4.7k pull-ups. R8 on SDO must be removed if the SD card is sharing SPI with the LCD panel. Otherwise the 10k (can be 4.7k to 10k) is unable to pass SDO to MISO.
You can use other diodes provided they have sufficient junction capacitance.
eg 1N400x series rectifiers work but 1N914 and 1N4148 don't unless you add 22pF to 150pF in parallel.