Current for Arduno Uno

Using Arduino General Electronics
1

Hi, I have couple of questions about electronics....very new at electronics...I am building a foozball table digital scoreboard.

  1. I want to power UNO from a power adaptor. I have a adaptor that provides 9v 300mA... Is the current fine for UNO?...if not what current does the UNO need...i know the volts needs to be between 7-12v.
  2. the sensor I bought requires 5v 100mA. I will be using the 5v pin to provide the power but that pin has 500 mA...how can I reduce the current without reducing the voltage?.

Thanks for any help!!

2

You misunderstand how current works and how it is rated. Current is drawn, not pushed. Power supplies provide a source of current, devices draw from that source. So your 100mA sensor will draw 100mA from a 500mA source.

The Uno, with nothing connected, draws on the order of 30 or 40mA.

Are you going to be using lights (LEDs?) for the scoreboard? If so, that's probably the biggest concern for current.

3

hi-

I suggest maybe looking into a shift register chip

and probably some 7-segment leds to use as your scoreboards..

2 x 7-segment leds for each 'side/team' (score)..

you could use just 1 MAX7221 chip for this (can control up to 8 x7-segment leds or 64 individual leds) (uses only one RSET resistor for all leds I believe)

or use a smaller shift register chip. (dont recall number off hand..but here in tutorial/playground).. that can control 8 leds.. so you'd need one for each 7-segment led you use.

Do you need two sensors? (1 for each side? so perhaps 200mA total?)

typically an leds uses 20mA.. (depends on specific led of course)..

Thats roughly 560mA just for the leds.. =)

4

Thanks for your help!!...yes I will be using 7 segment 4 digit led...so if I understand it correctly I can add the current requirement of all the LED and sensor and subtract it from the total current provided by the adaptor? And that will give me the total current I will require to run all stuff connected to UNO?

5

ahhh k now in am understanding how current works...thanks...I have thought of using the MAX chip to connect the led but for now I am just connecting one sensor and one 7 seg led just to get it working...I am pretty sure I will have more question once I do that :)...thanks again!!!

6

jat421:
Thanks for your help!!...yes I will be using 7 segment 4 digit led...so if I understand it correctly I can add the current requirement of all the LED and sensor and subtract it from the total current provided by the adaptor? And that will give me the total current I will require to run all stuff connected to UNO?

You almost have it. Add the current requirement of all the LEDs and sensors and the Arduino. If it is less than the adaptor rating, it will work.

Or put it another way: if you add it all up and subtract from the total current provided by the adaptor and you end up with a positive number it will work.

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