# Output voltage problems

Hey forum,

I've build a stand-alone arduino which functions as an arduino pro(3,3V;8MHz) w/ Atmega328. It functions perfectly and i'm using it with a gps reciever(UP501). The UP501 has 2 input voltage pins, a backup power supply and a main power supply. The backup-power supply is connected to +3.3V and the main power supply is connected to D2. The output voltage from D2 is 3.3V as expected, but when I connected the GPS to D2 the voltage drops to around 2.7V, where I need at least 3V. The 'normal' voltage on the back up power supply does stay at 3.3V. Can anybody help me out with this?

Regards,

Leo

leovanasch: Hey forum,

I've build a stand-alone arduino which functions as an arduino pro(3,3V;8MHz) w/ Atmega328. It functions perfectly and i'm using it with a gps reciever(UP501). The UP501 has 2 input voltage pins, a backup power supply and a main power supply. The backup-power supply is connected to +3.3V and the main power supply is connected to D2. The output voltage from D2 is 3.3V as expected, but when I connected the GPS to D2 the voltage drops to around 2.7V, where I need at least 3V. The 'normal' voltage on the back up power supply does stay at 3.3V. Can anybody help me out with this?

Regards,

Leo

If D2 is arduino digital pin 2 then your GPS probably tries to draw too much current from the arduino digital output pin. When running at 3.3vdc the recommended pin current limit is probably 20-30ma or less. So what is the current demand for the gps's power input?

Lefty

retrolefty: So what is the current demand for the gps's power input?

Well, I think thats the problem, It draws at around 35mA, any idea how I can make it work? With something like a relais probably?

you could just place a transistor with the base attached to D2, collector to +3V3 and emittor to the power supply

EDIT: with power supply i mean the one from the gps, and it has to be a NPN transistor (e.g. BC547 will do fine)

I agree with Lefty, you are trying to pull too much current through D2. It would work if you used D2 to control a transistor (or FET/MOSFET) to be able to switch power to the GPS module via D2. See http://www.oomlout.com/oom.php/products/ardx/circ-03 for a similar application (in this case a hobby motor).

Thank you very much, I think this will work

leovanasch: Thank you very much, I think this will work

Maybe not. Trying to switch the GPS's ground lead on and off through a npn switching transistor will probably also turn off the back-up power circuit for the GPS. You probably need to have a 'high side' switching circuit for the main power input of the GPS.

Lefty

retrolefty: Trying to switch the GPS's ground lead on and off through a npn switching transistor will probably also turn off the back-up power circuit for the GPS.

And if I use a PNP transistor?

leovanasch:

retrolefty: Trying to switch the GPS's ground lead on and off through a npn switching transistor will probably also turn off the back-up power circuit for the GPS.

And if I use a PNP transistor?

That is probably the correct method using a proper "high side" switching arrangement.

Lefty