Raspberry Pi Forums

Just started to delve into the GPIO of my raspberry, and so started off with the extremely simple one-diode circuit running off the 3v3 pin on the raspberry. To my surprise it did not work, and so I started to look for errors. When using my multimeter the measured voltage across 3v3 and GND is only 1.46V and not the expected 3.3V. I am powering it with an 1A usb charger, and voltage across TP1 and TP2 is 4.76V.

Proceeded and measured the amperage when a 330Ω resistor is hooked up, and got 4mA. If I'm not mistaken that would mean there is somewhere around 1.32V potential difference between 3v3 and GND (0.004A*330Ω = 1.32V).

Do you have any ideas as of why this could happen? Any help would be appreciated.

We may need more information about your

extremely simple one-diode circuit running off the 3v3 pin

If, as I suspect, you connected a LED either from a GPIO to ground or from the 3v3 pin to ground, without a series resistor, then it's possible you have blown up the LED, the 3v3 regulator, and/or the SoC.

measured the amperage when a 330Ω resistor is hooked up

How did you do that?
If you connected it so:
3v3 pin ---- 330Ω resistor ---- meter in current mode ---- ground
be aware that multimeters can have significant voltage across them in current mode, so your reading is likely to be inaccurate.

Remove all add-ons and measure the voltage on TP1-2. Should be 5v
Then measure the voltage on 3v3 pin to ground, without drawing any current from it.

Remove all add-ons and measure the voltage on TP1-2. Should be 5v
Then measure the voltage on 3v3 pin to ground, without drawing any current from it.

I'm sorry if my original post was a bit unclear on this point. This is exactly what I have done and the voltage between TP1 and TP2 was 4.76V and the voltage between 3v3 and GND was 1.46V, without drawing any current.

Hope this helps.


Jeremy

You are probably measuring the voltage between the 5V and 3.3V rails.

I agree with joan here.

Please describe the circuit in a bit more detail. Specifically which pins on P1 you connected the resistor and LED to. A brief circuit diagram like this will help

pin1-----Resistor------+LED------pin7

I have the same problem!! I am unable to light an LED using the 3v3 pin, and when i measure the voltage i only get about 1.14v. I'm sorry but I haven't found a solution.

Whether or not you have the same problem is uncertain, without more information.

Are you connecting directly to the pins on P1 on the Pi? Or using a breadboard? With a Cobbler?
What value series resistor are you using with your LED?
When you measure 1.14v, which pins on P1 are you using for 3v3 and ground (there are more than one of each), and how sure are you that you've correctly identified them?

If the Pi is booting, then there will be 3v3 available, it's just a question of finding it!

Other problems similar to this sometimes turn out to be a broken multimeter (or simply a flat battery in the multimeter)