Arduino shuts off when GND wire plugged in

Projects General Guidance
1

Hi there

My question is simple: Why would my Arduion UNO shut down when I connect the GND with in this setup:

07_LEDBarGraph.png
07_LEDBarGraph.png1755×1338 328 KB

2

What is the max resistance of your resistor pot?
If your resistance is too low then you might be pulling high amps through it and not leaving anything for the Arduino, (depending on what your power supply is).

If it's a high resistance, EG 100k, then check the resistance anyway to make sure it's not shorted out in any way.

3

I see a 10 led bar graph with each led a 220 ohm resistor.

current draw of each led, about

Amps = ( Vcc - Vf_led) / 220 ohms = (5 - 2) / 220 = about 14 mA but call it 15 mA each.
It may be a bit more or less since I used a guess of 2V for the led forward voltage.

All on, the bar graph alone should soak 150 mA.
Normal Arduino max current is 200 mA.
USB supplies 500 mA 5V, enough to power what I see. A battery may not.

And then there is the potentiometer that turned way down will suck like Microsoft... boom.
Try putting another 220 ohm resistor in the power going to that, it will limit the drain to about 25 mA at most.

  1. With some code, the bar graph can draw much less current at any one instant for a small loss in brightness.

  2. Stronger resistors on the bar graph leds would do the same.

  3. -or- try two 220 ohm resistors in parallel in the power line on the left that feeds the bar graph, if you use one resistor (100 ohm or more), make sure it is half-Watt or higher rated.

4

Simple check: when you remove Vcc from the bar graph, will connecting the Gnd line (to the pot, I assume?) shut down the system as well?

Use an ammeter instead of the Gnd wire, to find out how much current flows when connected. Same check for the Vcc to the bar graph wire.

Very unlikely: the bar has an unexpected pinning, causing shorts between output pins. Or the pot...

You can use one or more diodes in the bar supply line, instead of a resistor, to reduce the bar current by a voltage drop of 0.7V per diode.

5

GoForSmoke:
And then there is the potentiometer that turned way down will suck like Microsoft... boom.
Try putting another 220 ohm resistor in the power going to that, it will limit the drain to about 25 mA at most.

I'm confused about that statement. Potentiometer is between Vcc and GND; turning it way down or up will not change it's resistance.

6

I agree - I think GoForSmoke misread the diagram?

I'd wager that you're shorting Vcc to ground when you connect it - I think you should get out the multimeter and confirm that (don't power it up, just check resistance between them). I also suggest taking the pot out of the circuit and testing it with a multimeter to make sure it's really a pot (not a rotary encoder, which looks very similar), and hasn't suffered some catastrophic failure.

7

DrAzzy:
I agree - I think GoForSmoke misread the diagram?

Looks that way.