Wi-Fi sheild + relay = power conservation. Which Pin to target?

Projects General Guidance
1

The Wi-Fi shield is terribly greedy when it comes to power consumption. I need a way to utilize Wi-Fi when needed, but can't afford the regular power consumption.

Solution: I want to put the Wi-Fi shield on a breadboard, and connect it through wires to the arduino. I want to incorporated a normally open relay, which only allows power to go to the Wi-Fi shield when the relay is "charged".

My question are:

  • Which pin do I target? When I refer to pin, I am referring to the male end of the Wi-Fi shield that is made to insert into the female end of the arduino. Would it be the male pin that goes into the 5v pin on the arduino?

  • Will this work? or will the Wi-Fi code itself use the power even if the wi-fi shield wasn't attached?

  • Is there a way to do this using code only without a relay?

By the way, is there like a contest for arduino that users can summit prototype designs on youtube or something, and the winner chosen is awarded the resources to make the prototype power and size efficient to get it to market, or at least to impress investors?

Respectfully,
Thomas

2

Do you have a link to the board you are using?

Weedpharma

3

Sure I am using a Mega 2560 and the Arduino Wi-Fi Shield because the shield stacks on the arduino, I thought all arduinos would power the shield through the same male pin on the Wi-Fi shield. That's why I didn't think to list the board.

4

I haven't tried it, but you should be able to cut off the power to the shield with a relay. AFAIK, there is no way to put the wifi shield into a "standby" or "sleep" mode.

Remember that when you turn on the power to the wifi shield, you must run the setup functions again.

It appears that you can power the wifi shield through the 5v pin or the ICSP connector 5v pin.

5

If you're going to cut the 5V power to the shield, make sure to bring all control lines low first so the shield isn't powered by Arduino High outputs thru protection diodes on input pins.

6

AFAIK, there is no way to put the wifi shield into a "standby" or "sleep" mode.

Poor designing then. The Engineers should have understood what they were designing was a prototype platform. A prototype is preferred to run off batteries when you finish the grand design and wish to show investors. If the Wi-Fi shield drains the battery's... They should have understood that and incorporated it into the shield, so that the arduino could be run on batteries.

Remember that when you turn on the power to the wifi shield, you must run the setup functions again.

Of course! Already have that figured out. - By the way crossroads, if I wanted a Eagle board shield that had the relays I needed built in, so I could stack the Eagle board between the Mega, and Wi-Fi shield, how much would you charge me for that? Would you do it for $35, plus whatever the cost of the parts needed, and shipping ends up being?

It appears that you can power the wifi shield through the 5v pin or the ICSP connector 5v pin.

So cutting either one would work, similar to cutting the ground, or power line works? Or are you saying I need to cut both?

If you're going to cut the 5V power to the shield, make sure to bring all control lines low first so the shield isn't powered by Arduino High outputs thru protection diodes on input pins.

Whoa... how do I do that? Do I need to write code that tells pins 4, 7,10,11,12,13, 50, 51, 52 to all go low before cutting power?

7

You need to bring low every pin that the WiFi shield uses.

8

I want to keep pins 1-12 free so I can stack other shields on the arduino in the future without having to disconnect, and re-connect the wires that lead to the relay that control the wi-fi shield.

Is there a way to re-program the pins that the Wi-Fi shield uses so that I can use the spare pins (pins 30+ on the mega) to control the Wi-Fi shield?

If not, how hard would it be to make an Eagle board that has the needed relay's built in?

9

I have read somewhere that holding the shield in reset will cut power consumption.
Don't know how much, or if it's even true.
Leo..

10

The theory to reset is it's like using an off button, while held down. I don't know if it would work either, but it's an interesting theory. Would be more interesting if you didn't have to physically hold down the button though, you can't exactly use the arduino to activate a servo that does that, or it would never turn itself back on.

11

Reset is just a logic level. You can use an Arduino pin to keep the shield in reset.
Maybe use a 220ohm resistor between pin and reset line.
You don't want any trouble when someone pushes the reset button while the output pin is high.

All you have to do is separate the shield reset from the Arduino reset.
Bend the reset pin out of the way when connecting the shield to the Arduino.
Then connect that reset pin via a 220ohm resistor to an available output pin.
The code does the rest. "low" is shield in reset, "high" is normal function.
Give the shield some time to start up.
Leo..

12

Which pin is the reset?

13

Next to the 3.3volt pin, according to the pdf on the "Arduino Wi-Fi Shield" link in post #2.
Leo..

14

I mean the shield reset pin.

15

Yes, the shield has a reset pin that plugs into a connector of the Arduino.
It is labled "res" on my UNO, and "reset" on my Mega.
You can find it next to the 3.3volt pin, on the DC jack side.

|reset|3.3volt|5volt|gnd|gnd|Vin|

I see now that it is not easy to bend the pin out of the way, so you might have to unsolder it.
Leo..

16

Does the reset button reset the Wi-Fi shield, or just the Mega which would of course power down the shield?

Your theory of leaving 3.3 volts hooked up to the Wi-Fi shield would probably work, but my normally open relay system is more power efficient, as it would only use the 3.3 volts when the shield needs to be on, which is lest often than it needs to be off.

Where can I get a male to female extension? I want to use the extension on the needed pins, so I don't have to bend or unsolder my $80 Wi-Fi shield. I also need that space so I can put in the relay.

What is your profession Leo? You caught my attention a few months ago when you first started on the forum. If this works can you make me an eagle board that has this relay built in if I pay you?

Do I need to put the normally open relay on the 5volt pin of the wi-fi shield or the ICSP connector 5v pin of the wi-fi shield, or both?

17

Thomas499:
Does the reset button reset the Wi-Fi shield, or just the Mega which would of course power down the shield?

The reset lines of the Arduino and the WiFi shield are in parallel.
If you press the reset button on the shield or on the Arduino, both will reset.
I suggested to separate the two reset lines by removing the pin that links the two boards.
Cutting a track is also possible. Both interventions need soldering skills.

I had another look at the schematic diagram, regarding cutting power to the shield.
I saw that this shield (post#2) is using a DC/DC converter to generate 3.3volt from the Vin line, or from the 5volt line if Vin is not available.
As far as I can see, most things on the shield are powered from this 3.3volt line.
The DC/DC converter (LM2736) has an enable pin (pin 4).
That could be pulled low with the collector of a small transistor.
Adding a small transistor with a 10k base resistor would be an easy way to silence the shield.
But again, you need good soldering skills for that.

@ Thomas499
I was a consumer electronics tech for most of my life. In that profession, you need to know a bit of everything.
Leo..