Go Down

Topic: General advice on my project (Read 469 times) previous topic - next topic

erbedo

Hi
    I need to power up an external device which uses 3V batteries with arduino, based on a GPRS call. I already have the GPRS shield, and this is working fine, I can switch on a pin whenever I want. The problem is about the circuit needed.

I tried to use the 5V ouput into a transistor controlled by the base, a 27 Ohm resistor and then connect it to my device, but this doesn't work. So I tried to use my out pin (which gives me around 4.5V) and use the same resistance, and then this goes to my device's + pin, but this didn't work either.

I am pretty newbie on electronic, can anyone give me an advice to do that?

Thank you very much

HazardsMind

Did you try the 3.3v pin on the arduino?
My GitHub:
https://github.com/AndrewMascolo?tab=repositories

Grumpy_Mike

A 27R on the base is far too small make it a 2K7 at least.
Are you trying to control the power to this device or send a signal to it?
If a signal then :-
Then on the collector you need a pull up resistor, say 1K to the 3V line.

erbedo


Did you try the 3.3v pin on the arduino?


If i connect it to the 3.3 pin, i got 2.6 v since 0.7 is drained by the transistor.

erbedo


A 27R on the base is far too small make it a 2K7 at least.
Are you trying to control the power to this device or send a signal to it?
If a signal then :-
Then on the collector you need a pull up resistor, say 1K to the 3V line.


I'm trying to give power to it.

I used a 27 resistance since i used the ohm law: 1,3/0.05 = 27?

Did i get something wrong?

PaulS

Quote
Did i get something wrong?

Maybe. Where did the 1.3 and 0.05 come from?

erbedo


Quote
Did i get something wrong?

Maybe. Where did the 1.3 and 0.05 come from?


1.3 is the voltage i want to drain (from 4.3 to 3) and 0.05 is 50 mA, which is the current that the Vout pin has.

Grumpy_Mike

Quote
I used a 27 resistance since i used the ohm law: 1,3/0.05 = 27?

Did i get something wrong?


Yes this is not the way to do anything. You can not use resistors to reduce the voltage.
You need to get a 3V voltage that is capable of powering your device. How much current does your device take?
Then you need to switch that with a transistor.
Arduino output -- 2K7 --- transistor base
Transistor emitter to ground
device ground to transistor collector
device power to your 3V supply +ve
3V supply ground to arduino ground.

winner10920

Perhaps th best way would be a low dropout 3.3v regulator, 
or second maybe cheaper just 2 plain diodes to drop 1.4 volts to 3.6, maybe a germanium diode to drop aanother.3v, that will work the only problem is the voltage dropped changes slightly with current being drawn

Go Up
 


Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

Arduino
via Egeo 16
Torino, 10131
Italy