arduino pins in parralel

Hello. My goal is to control 2 relays with the arduino without the use of transistors. I understand it is a lot better to use transistors but I do not have immediate access to them. The relay itself draws 72ma. Each arduino pin can supply 40ma and the total current that can be drawn from the 1/0 port is 200MA. Now with that out of the way can I tie twould arduibi pins together to achieve an output of 80ma? I'm typing from a smartphone so forgive my grammar. Thanks

In theory, usually much different from reality, if the Arduino is perfectly manufactured that MIGHT work. Any small mismatch and you could have a problem. Not worth the risk compared to just getting a relay or transistor. Patience is not a virtue here. It is a tool. Use it. Immediate vs blowing your board because you didn't use a 2 cent transistor? http://www.taydaelectronics.com/t-transistors/2n-series/2n3904-npn-general-propose-transistor.html

Thanks a lot! I have a collection of about 20 arduino Nano clones so I'm going to give it a shot. I'm making a digikey order at the end of the week. I just don't want to pay $8 shipping for a 2 cent item

Ennsjosh:
Thanks a lot!
I have a collection of about 20 arduino Nano clones so I’m going to give it a shot. I’m making a digikey order at the end of the week. I just don’t want to pay $8 shipping for a 2 cent item

40mA is the “absolute maximum” current that can be drawn from one pin, not the “recommended” amount.
Even if paralleling pins was a good idea, you’re too close to the borderline at 36mA per pin. And unless you use bitwise operations to switch both pins at exactly the same time, both pins won’t switch at precisely the same time, and the first will take the brunt of the 72mA load. digitalWrite() takes a little time to execute, so the first pin you write to will turn on slightly earlier.
Be patient and wait for the transistors to arrive, then do it properly.
After all, why did you even post this question if you’re going to ignore the advice that you’re given anyway?

Edit: Also, in that moment when one pin is high and the other is low, they’ll form a short circuit since they’re connected together.

Ennsjosh: Thanks a lot! I have a collection of about 20 arduino Nano clones so I'm going to give it a shot. I'm making a digikey order at the end of the week. I just don't want to pay $8 shipping for a 2 cent item

$1 to ship the 2 cent item from the place I listed. How much is your clone?

outofoptions: $1 to ship the 2 cent item from the place I listed. How much is your clone?

Yep, and actually he'll no doubt need more small transistors in the future, so he could buy a decent number now, and always have some on hand when needed, to avoid going through this again in the future. However, I think he's already made up his mind to go ahead regardless.

And if he's in a country that has an RS Components outlet, delivery is free for all online orders, and very fast. My orders always arrive within 2-3 days if the parts are in stock, and if not they ship them in from overseas within a couple more days at no cost to me.

Ennsjosh:
Hello. My goal is to control 2 relays with the arduino without the use of transistors. I understand it is a lot better to use transistors but I do not have immediate access to them. The relay itself draws 72ma. Each arduino pin can supply 40ma and the total current that can be drawn from the 1/0 port is 200MA. Now with that out of the way can I tie twould arduibi pins together to achieve an output of 80ma?
I’m typing from a smartphone so forgive my grammar. Thanks

If you really must do what you are suggesting,
then follow these ideas to minimize the risk of damage …

For Relay # 1 …

  1. Use three pins ( like D11, D12, D13 ) all from the same PORT B
  2. “OR” the three Digital I/O together using one diode per Digital Output Pin
  3. Use “PORTB” type of Direct I/O code to change all three Digital Outputs simultaneously.
  4. Add a reverse bias diode on the coil to suppress inductive kick-back
  5. Connect the Relay to Ground and to all three didoes
  6. Set the all three Pins HIGH to output +5 Volts via the three diodes

For Relay # 2 …

  1. Use three pins ( like D17, D18, D19 ) all from the same PORT C
  2. “OR” the three Digital I/O together using one diode per Digital Output Pin
  3. Use “PORTC” type of Direct I/O code to change all three Digital Outputs simultaneously.
  4. Add a reverse bias diode on the coil to suppress inductive kick-back
  5. Connect the Relay to Ground and to all three diodes
  6. Set all three Pins HIGH to output +5 Volts via the three diodes

If you follow the suggestions above then
you might have a chance of making the relay function.

Disclaimer of any liability:
This is never recommended and it may damage your Micro-controller.
Proceed at your own risk.

Pin Current Limitations
.

$1 to ship the 2 cent item from the place I listed. How much is your clone?

Ha ha, $2 clone

raschemmel: Ha ha, $2 clone

@#$% that's cheap. It's got me buggered how the Chinese can do it, and free postage to boot! Try buying the individual parts in our countries. It would cost a (relative) small fortune to make one of those boards, then post it overseas.

@#$% that's cheap

I never bought that one but I bought a $3 clone, $1.49 shipping , 7 day delivery from china

A hamburger costs more than that.

raschemmel: I never bought that one but I bought a $3 clone, $1.49 shipping , 7 day delivery from china A hamburger costs more than that.

Yeah, pretty amazing, isn't it? I get good-quality UNO clones for AU$8 delivered, (USD$5.76). They have an ATMega USB to serial chip, too, not that troublesome CH340G. The only downside is that they take 3 weeks to arrive. I can live with that. :D

mrsummitville: If you really must do what you are suggesting,

Then don't!

That really is the end of it. :roll_eyes:

Very poor engineering practice