$20 LCR ESR Transistor checker project

[Feliciano]

An issue here is nobody sells SMD components, so sometimes I depend on scavenging things.

I tried the option of the 2x 1N4148 (apparently more power-efficient, and it could have worked considering the original Q was around 4V for everything). But the backlight is still washing away the black. I'll keep scratching my head about this. Perhaps reducing its bright with a resistor? or I don't know if I would have to insert series resistors on the data lines? As I read, Karl-Heinz implemented setting the LCD lines as open collector (OC) and tweaking the pull-up in order to aproximate to 3.3V. I don't know whether the m-firmware has a similar workaround.

Besides that, maybe I will have to look at the ST7735.c as well. Or even cut the frame as suggested.

Additional comments:
.-Regarding the reference to blank offset settings, please note there's the same suggestion for the BSide
.-I also think this one is a runner for the crown of the sloppy designs

[madires]

Yep, if the backlight is too bright try a larger resistor. The in-series resistors for the data lines (in conjunction with the ST7735's protection diodes) are a quick n' dirty level shifter. The m-firmware doesn't support an open-collector mode (would open a can of worms when driving multiple ICs or when switching to hardware SPI).

[Feliciano]

And I'm curious about another fact: what the OSHW firmware LCD driver does different during the firmware flashing procedure, compared to normal operation? Because in those seconds the black part of the screen works as it should.

[madires]

During flashing the firmware doesn't run. The display will show whatever is in its memory at that time. AFAIK, the Fish8840 drives the ST7735 with 5V directly instead of using in-series resistors. So the ST7735's Vcc would get 5V minus a diode drop via the built-in protection diodes when any signal is high. For example, the TC-1 uses 10k in-series resistors plus a 3.3V LDO. The resistors limit the current and allow the LDO to keep Vcc at 3.3V.

[indman]

 It’s a little strange that most Fish8840TFT owners did not complain at all about the display and its brightness when using OSHW firmware? Experience has shown that many displays do not experience problems with the 5V level on the signal buses(VDD=3.3V), although it is still technically correct to coordinate these levels not using resistors, but using at least 4050 

[madires]

There are different versions of the ST7735:
- ST7735
  - I/O Voltage (VDDI to DGND): 1.65V~VDD (VDDI ≤ VDD)
  - Analog Voltage (VDD to AGND): 2.6V~3.3V
- ST7735R
  - I/O Voltage (VDDI to DGND): 1.65V~3.7V (VDDI ≤ VDD)
  - Analog Voltage (VDD to AGND): 2.3V~4.8V
- ST7735S
  - I/O Voltage (VDDI to DGND): 1.65V~3.7V (VDDI ≤ VDD)
  - Analog Voltage (VDD to AGND): 2.5V~4.8V
And possibly some compatible controllers.

[Feliciano]

Interesting, and thank you all for the feedback.

So for the unit in hand, i.e. m328p+GMT177-05 (ST7735S), if the driver is not refreshing the screen (I/O=0V, I suppose) the colors are OK, but all the colors are "overdriven" when running the out-of-range of Vdd=3.6-100*I and I/O up to 5V-Vsat. (I didn't pay much attention to the screen when running the original firmware with 5V//3.3V=4V, though).

Nevertheless, according to the quoted specs I set Vdd=5-100*I, and that apparently solve this part of the issues, thanks.

Now the unit worth a little more, and I will play around with the settings trying to avoid removing the ugly yellow glue, cutting the box, and putting all back toghether without damage.

[Feliciano]

With the simplest hardware mod and some atypical settings, I think I'm getting there:

Code: [Select]

#define LCD_DOTS_X       128
#define LCD_DOTS_Y       158
#define LCD_OFFSET_X     1 
#define LCD_OFFSET_Y     6
#define LCD_FLIP_X
#define LCD_ROTATEAnd one of my narrow fonts due this odd screen frame size.

My original intention was to run K-firmware (16M) on this one, but I'm not sure on whether I could replicate something similar on those config files, so maybe I'll leave it as is.

Cheers.

[Yuriy_K]

A question for everyone who managed to make a k-firmware for FISH 8840.
What values ​​are in your config.h?

Changed display pin configuration.
Try new firmware at the end of the previous page...

[Feliciano]

To put this in context, the Fish8840TFT seems to have a different LCD pinout than the k-firmware's default. Apparently this was properly considered for the older Rev804 shared on Yandex, but looking at the long and nested if-then-else of config.h pointed out by Yuriy_K, it's different on the current trunk. It could be related with the fact of blue or green variations of this board, I'm not sure, but if that's the case, it should be added a separate branch with the proper note. (I suppose it should be also different from the unboxed monochrome versions).

In any case, the PCB I have is the blue one, works with the binaries shared on Yandex, and/or Yuriy_K on the last page, and also with the one I make now.

Code: [Select]

CFLAGS += -DLCD_ST7565_H_OFFSET=7
CFLAGS += -DLCD_ST7565_V_OFFSET=2 /* garbage seen when looking from below */
CFLAGS += -DBAT_OUT=200
CFLAGS += -DBAT_NUMERATOR=66
CFLAGS += -DBAT_DENOMINATOR=33

I will now play with both firmwares to choose what I like best.

Thanks,