Quickstart + LCD + 9V

laurent974

Hello,

i would like to connect a 9V battery to the quickstartboard and the LCD be powered from the board.

Which pin should i use ?
LCD : RX = pin 12
gnd = pin 39
5V = pin ???
9V: + on pin 40 and - on pin 39

I have fried my previous quickstart board by misconnected the 9V on the little holes. now i'm a bit reluctant to try something.

JonnyMac

If you want to use the LCD with your project, you're going to need a regulator because Vin (pin 40), goes to the 3.3v regulator. There is no 5v regulation on that board.

kwinn

I would suggest using a 5V switching regulator between the battery +9V, the LCD, and the Quickstart Vin pin. That will provide more current and longer battery life than using a linear 5V regulator.

laurent974

thank you,

Another solution :
Could i use a USB standalone smartphone charger instead of 9V battery? (i have a revB quickstartboard)

I'm currently using a USB wallplug.

JonnyMac

Don't use a charger, use a 5v supply (they're different). 5v supplies with USB micro plugs are easy to come by (look for RPi accessories), but the QS board uses USB mini.

Maybe something like this:
-- https://www.amazon.com/SoulBay-Replacement-Versatile-Regulated-Electronics/dp/B07BXW19R7

Jeff Haas

Ideally you want to split the power so the LCD gets the 5V directly from the supply, instead of from the Quickstart. If you power the LCD directly from the Quickstart it will be dim.

cavelamb

I run serial 2 line LCD from 3 and 4 cell AA packs. 4.5 to 6 volts nominal.

Run the LCD directly from the logic battery.
At 4 volts is was necessary to adjust the contrast to read the display.
But it wasn't visible at all on 3.3VDC.

I think the LCD controller was running. But the display was not readable.