Too much going on via one pin ?

Hi there,

I have the following:

Arduino Mega 2560
Ethernet 2 shield
2 relays (like the one included)
Lcd 20x4 with I2C (PCF8574)

The Ethernet shield is obviously connected to the arduino mega.
The 2 relays and the LCD is wired to the onboard 5v pin and ground for power.

Is this too much current to draw from one 5v pin ?

I have read that 20mA should be the limit.

xelot: Is this too much current to draw from one 5v pin ?

I have read that 20mA should be the limit.

It depends on how you power the Mega.

The Mega itself draws ~70mA. One relay draws about 75mA when active. A W5100 ethernet shield draws 160-180mA. Don't know about the LCD. could be ~50mA. Most of it would be backlight LED current.

I/O pin limit is 40mA (20mA recommended). 5volt pin limit of a Mega on USB supply is 500mA (polyfuse and/or PC/laptop limit).

Limit of the 5volt pin with 7.5volt on the DC socket is also about 500mA (5volt regulator temp limit), but that drops to ~150mA on a 12volt supply. Leo..

The arduino is powered by a usb cable and a ‘mains-to-usb’ converter for a iphone.

Wawa:
The Mega itself draws ~70mA.
One relay draws about 75mA when active.
A W5100 ethernet shield draws 160-180mA.
Don’t know about the LCD. could be ~50mA. Most of it would be backlight LED current.

I i add all the numbers it comes to 450 mA. And then some of the figures are not even for sure.

What happens if the 500 mA limit is exceeded ?

Would you give some of the elements fx. the LCD and one of the relays a seperate power supply ?

xelot: What happens if the 500 mA limit is exceeded ?

Would you give some of the elements fx. the LCD and one of the relays a seperate power supply ?

1) On USB supply an onboard 500mA polyfuse might trip (and automagically fix itself after a cooling down period). But ~450mA can be sustained. Don't forget that the relays draw 0mA when not active.

On DC socket (external supply), the regulator will get warm (or hot), depending on supply voltage.

2) Seems not needed if... on USB supply or you keep external supply <9volt.

So how are you going to power this setup. Leo..

The problem i am dealing with is that some times the display 'freezes'. And the values sent over the ethernet shield sometimes return as 0 - which it shouldn't. it is always a certain number between 1 and 1250.

That is why i started suspecting the power.

I have a similar setup with only one relay that works perfect. I think i'll try to shut off the second relay, and see if it has an effect.