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sudo ./hub-ctrl -h 0 -P 2 -p 0 ; sleep 3; sudo ./hub-ctrl -h 0 -P 2 -p 1
In the meantime the manafucterer has confirmed that backlight control is not possible and the retailer has apologized for the mistake in the product description of the sainsmart display.. Backlight control is definitley not possible without upgrading it like you have done it.saper_2 wrote: I didn't found anything that could suggest the backlight can be controlled. Looking at those low-res photos I can only tell that BL circuit is made on PT4103 (this circuit looks identical). I don't see anywhere any mentions about BL control nor there is no solder pad (or goldpin) to connect to free GPIO for controling BL.... I'm pretty sure that's finding a display with BL control (with HDMI & USB/SPI touch) will going to be really hard, easier is just hack a display , wait, no, that isn't hack, that's an upgrade
Could you post some schematics of your solution? You have connected transistor directly to backlight's switch and left it in off position, right?JohnsUPS wrote: ↑Mon Dec 10, 2018 2:24 amI bought an inexpensive 5" LCD panel for a recent project, and I needed a way to turn the backlight on and off. The display had an on/off switch on it, so instead of cutting traces, I added a couple of mosfets.
I measured the backlight currrent, which was ~107ma. The mosfets I used were rated higher than that, but I designed and installed the circuit prior to measuring the current. I could have got away with just using one.
What I did was use two TP2104N3 P-channel mosfets in parallel (it is what I had laying around). I used P-channel mosfets because they can be connected right across the switch. One side of the switch is +5v, the other is the backlight. It is because one side of the switch goes to +5 rather than one side of the switch going to ground that necessitated the use of a P-channel mosfet. The gates are connected together and switched by a 2n3904 to ground, and the base of the 2n3904 goes to a GPIO pin through a 1k or so resistor. I could probably do away with the transistor, but I typically follow any GPIO pin with a transistor to protect it. Works like a charm.
The backlight could also be dimmed with this circuit by providing a variable duty cycle signal to the GPIO pin.