Is a 5 volt 2.5 amp power supply ok for arduino and lcd screen

I tried a 5v 2.5A powersupply on and arduino with a LCD screen and the lcd went into a dull flicker. When I connect the arduino by 5v usb cable the lcd is fine.

Does the lcd need more contrast, as the 10k pot I use for the contrast is as far as it can be adjusted, or fully anticlockwise.

Which Arduino and exactly how did you connect the 5V supply to it? It should be connected to the 5V pin not to Vin or the barrel socket which need higher voltages.

Steve

It is an Arduino UNO, and I connected the power supply by the barrel socket on the fron of the arduino.

I've used 9v power supplies with barrel jacks to power arduino's with led strips before, and though a 5v would be ok. Apparently not tho'

avalon66: It is an Arduino UNO, and I connected the power supply by the barrel socket on the fron of the arduino.

I've used 9v power supplies with barrel jacks to power arduino's with led strips before, and though a 5v would be ok. Apparently not tho'

The barrel connector feeds to a reverse polarity protection diode and linear regulator that results in a loss of around 2 volts, before it gets to the Arduino, and to the "5V" volt pin. In other words, the printed "5V" is hopeful but not necessarily true. It's veracity depends on adherence to specifications, such as "7 to 12V" on the Barrel connector.

Ok so in simple language are you saying I should use something like 7 or 9volts then

avalon66: Ok so in simple language are you saying I should use something like 7 or 9volts then

Yup.

But, check out this discussion: https://electronics.stackexchange.com/questions/65576/arduino-uno-r3-directly-supply-regulated-5v-to-5v-pin

BUT

The official stance, from the Arduino website is:

Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

URL of source of above quote -- under Documentation tab - section Power: https://store.arduino.cc/usa/arduino-uno-rev3

avalon66: Ok so in simple language are you saying I should use something like 7 or 9volts then

You could do that or you could simply connect your 5V supply to the 5V pin...provided it is a proper regulated power supply. That's what I normally do.

Steve

I really want to use what I already, and that is power supplies with barrel jacks.

To connect to the 5v pin, what is required for that.

Something like this? Make SURE polarity is correct before wiring to Arduino, check with DVM if you have one. https://www.amazon.com/Female-Barrel-Connector-Cameras-LED/dp/B01M0P34E8/ref=sr_1_13?keywords=barrel+jack+adapter&qid=1550611390&s=gateway&sr=8-13 Wire from + terminal to 5V pin, wire from - terminal to GND pin.

I have already got one of those barrel socket, so I'll get it sorted later.

Thanks