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"Playing around” (those of us who used to get paid for such frivolity always called it research or some such) is wonderful: never stop!

The display backlight isn’t quite ‘unnecessary': without it, you’re shut down or flying blind, I suspect.

The math is fairly easy. If the Raduino takes 200 mA (say), that regulator is dissipating, with 13 VDC input, (13-5) * 0.2 =1.6 watts. If you put in a moderately efficient switching regulator - say 80% - it’s delivering 1 Watt at 5 V and consuming 1 watt/0.8 =1.25 watts input. Note that the switcher is dissipating 0.25 watts, as opposed to 1.6 watts with the 7805. These little switchers (built around a 34063 or its more efficient brethren) are wonderful things for cool-offs and battery life. That's why we see them everywhere.

Note that this approach leaves the Nano (16 MHz problem gone) and the display (brightness problem gone) both running at 5 V, while saving 1.25 watts. It’s almost like getting something for nothing, but we’re wise enough to know that that will never happen.

On a completely different front of the same battle, stuff I’ve designed over the years, if battery operated, dimmed or extinguished the backlight 10 seconds (or whatever) after the last user input, and lit it up again at any sort of a user touch. Many of those devices were fairly exotic things (laser/GPS surveying equipment, generally), yet the greatest current hog in the whole shebang was the display backlight. This seemed a cosmic injustice to me. But there it is. And I’ll bet we could do it with the Raduino, although, on a cursory glance, I don’t see a separate backlight input to it on the Raduino schematic. Does such a thing exist on that display?

t

On Feb 15, 2025, at 11:10?AM, Gary Anderson via groups.io <gary.ag5tx@...> wrote:

Ted,
I was hunting birdies, not looking for ways to reduce power.

Above all, I’m sorry if my silly comments seemed like a rebuke to you: nothing was farther from my intention. I’d hoped for nothing more than the innocent tossing of ideas back and forth!

Sadly, I’m at sea with ‘birdies’… Is that a spurious RF signal (as I suspect) or something else?

I was just sharing the power outcomes from what I did during a bird hunt, and also called my voltage dropping on the Nano a kludge. That was not my recommendation as the path forward to reduce power. Agree that a switcher would be more power efficient. We already have three oscillators and now add a fourth? Even as such, the LED backlight will consume more power when still biased at 5V (and to a lesser degree the ILI9341). That's what I meant by unnecessary. I was not clear. Better stated as It's very wasteful to bias the backlight at 5V, when it is designed to work at 3V.

Quite so! Back before the snow got really deep, I had the thing outside and (as with most such devices) the display isn’t as readable as it is inside. Maybe it needs all that backlight for a POTA-like activation?

If going down the added efficiency of a switcher, you'd also not use the 3.3V regulator on the display board and supply your own 3.3V.
The challenge/issue with the Raduino's Nano is code space to add microcontroller control of display backlight. The backlight On/Off as well as display brightness can be controlled via SPI. Educated guess that brightness is done with PWM. This would save power (especially with 5V applied) but a high potential to add more noise, the opposite path I was going down at the time.
When you looked at the Raduino-TFT schematic, you should have seen the backlight control hard wired. I stated "switch between R1 and +5V on the Raduino-TFT to turn off the backlight" and provided a link to the website for the display information so you can see the backlight control.

Thank you for that tidbit: I’d not looked at the display’s connections (from the display side), and didn’t realize that R1 on the Raduino was the bullseye. Nor did I realize that there’s a 3V regulator on the display.

There is a bewildering variety of requirements (low noise, low power, bright (or, more properly, readable) display), and an even more bewildering array of potential solutions. Whether my switcher significantly adds to the chirps and whistles in my room full of computers and test equipment, I really can’t say. No doubt it does, but there are so many to steer around now that I didn’t get annoyed by any new ones.

In a very recent post, DaveW, KL7HJF has mentioned that many of these display power foibles have been addressed!

Again, I’m very sorry if my blather was offensive.

t

Regards,
Gary