Hello Everyone,
I'm new here but been lurking for a while.
I received the Fish8840TFT in the mail 3 days ago through aliexp.
I've played with the input voltage and here are the results
Input Voltage / Result9v = Working (7.8v on display / 320 ma current consumption) 7.8v x 0.320 = 2.88 watt
8.5v = W (7.7v / 300 ma)
8v = W (7.7v / 280 ma)
7.5v = W (7.6v / 260 ma)
7v = W (7.5v / 230 ma)
6.5v = W (7.5v / 190 ma)
6v = W (7.4v / 160 ma)
5.5v = W (7.3v / 110 ma)
5v = W (7.4v / 70 ma)
4.5v = W (7.6v / 50 ma)
4.3v = W (7.6v / 50 ma)
4.2v= W (7.7v / 50 ma)
4.1v = Screen flashes but unit does not switch on. Issue with dropout voltage of zener diode 3.3v (BZX84C3V3). Atmega328 working voltage is 1.8v to 5.5v
Tested on 2200uf capacitor. Zener diodes may probably not work.
Changing input voltage changes the reading data and so needs calibration (join 1+2+3 with small wire and switch on unit. Needs good 100uf capacitor)
Btw, I desoldered the LCD connector flex cable to see whats inside. I would advise readers not to do that since resoldering this back is a pain. IMO, we can desolder/resolder this 3-5 times max before the pitches start disintegrating due to heat. Also set 200-250C heat on solder for this. My resolder attempt was horrible and I had to cover it with tape just to avoid looking at it.
Some components get warm to hot during operation. When powered by 5v Vin, components run cool (ie, at room temperature)
Next mod is to add lithium battery. BZX84C3V3(3.3v) zener is getting hot because it is connected directly to 9v Vin and dropping 5.7v. A stable Vin should be 5v though 3.6v lithium + a
tiny booster.
More photos here
https://imgur.com/a/kTM8BPx