During the development of the software, I noticed several times that the raspberry didn’t interact after the ADC program was running for one day.
Since the seismometer needs to work many days outside without manual operation at the raspberry, this gave me some worries.
Therefore, I took a peek at the log file /var/log/syslog and I found out that there have been hundreds of “Under-voltage detected! (0x00050005)” messages every day.
Under voltage is a serious problem, if you want your raspberry run continuously, as the raspberry turns of several moduls like USB and network, and sometimes the moduls doesn’t get turned on later. Also the ssd runs over USB, which means data might get lost and files get corrupted.
After trying several power supplies, some of them deliver up to 4 A, which is far above of what a Raspberry needs, the problem still occured.
Now I measured the voltage at the 5 V GPIO pin of the Raspberry, while running the ADC program. The voltage at the GPIO pin was only 4.5 V. This is much to low. The voltage at the power supply was around 5.1 V, so there is a voltage drop of about 0.6 V between the micro-USB power input and the GPIO pins.
Next I measured the current throught the micro-USB power input: 0.52 A. This is quite low and it shows that the power supply is not the problem, but that the voltage drop of about 0.6 V at 0.5 A is probably a development bug of the raspberry 3 model B 1.2.
Even though some people don’t recommend to power the raspberry 3 over the GPIO pins, while other people recommand exactly that, I tried it by myself.
After connecting the 5 V of the power supply to pins 2 and 4 and ground to pins 6 and 34, the voltage was 4.98 V, and the current 0.51 A, perfectly.
The 3.3 V is produced by the raspberry itself using a little switch mode power supply unit on board.
In the next days I didn’t had any under-voltage messages and the raspberry run without problems.

 

Voltages and currents

Voltage of power supply

The power supply has a voltage of about 5.1 V.

Voltage at GPIO using the standard micro-USB power input

The voltage at the GPIO pin using the standard micro-USB power input was only 4.5 V, which far to low.

Current of power supply using the standard micro-USB power input

The current using the standard micro-USB power input was 0.52 A, which is fine and no problem for the power supply.

Voltage at GPIO using the GPIO power input

The voltage at the GPIO pin using the GPIO power input was 4.98 V, which is fine.

Current of power supply using the GPIO power input

The current using the GPIO power input was 0.51 A.

Circuit diagram

Instead of using the micro-USB power input: the 5 V of the power supply go to pins 2 and 4 and ground to pins 6 and 34. That’s it, quite simply but effective 🙂 .