recommendations for low power sbc

[johanvdw]

Hi all,

 

I'm looking for an sbc with low power consumption, but still able to run linux (arduino like solutions are somewhat unflexible, and take longer to configure). Basically it should be able to do rs232 and be able to store data to an sd card.

It should be able to run approximately two weeks on batteries. Wifi/ethernet/hdmi are not required if there is a way to use a serial console (apart from the extra rs232 which is connected to our measuring device).

 

I already own a banana pi (original) and raspberry pi zero (apart from other boards which draw much more power). Are there any boards I could check out that have significantly lower power usage?

[tparys]

Unfortunately, there's not really enough here to go on. How much data are you recording, how frequently, and what sort of processing do you need?

 

Also, "batteries" is also ambiguous. Most of the supported boards would probably run for a month off a 12V car battery.

 

As a general rule, I'd browse the download page and look for smaller boards without heatsinks, and check the datasheets for typical power usage, and what sort of I/O is available. Honestly, you might just need to get a few and try them. Most aren't that expensive.

 

I'd also leave off WiFi and Ethernet unless you really want it. Those will drain far more power than a 232 serial connection.

[johanvdw]

On 10/6/2021 at 4:26 AM, tparys said:

Also, "batteries" is also ambiguous. Most of the supported boards would probably run for a month off a 12V car battery.

Thanks for you answer so far.

 

Some math: Based on https://www.jeffgeerling.com/blogs/jeff-geerling/raspberry-pi-zero-power :

with some tweaking the power consumption of a raspberry pi A+ is 0.4W or 80mA at 5V. That would equal to 40mA at 12V allowing some losses in the power conversion. A car battery has a rating of approximately 50 Ah. So it would allow running for 50000/40/24/7 = 7 weeks . While that's could work in theory, I'm mostly wondering if there is another board I could use. 

 

My processing needs are quite nimble. In fact dumping all data to sd and turning off/on the sensor at regular intervals would do. Perhaps I will look to more arduino like solutions in the end.

[Heisath]

Arduino solutions will be the only more efficent way going forward. I mean, reading RS232 to SD card is super simple. 

 

Untested code below, it would watch Serial and SoftSerial for incoming data, write it to a file on sd card (in 100 char chunks or on every newline, syncing sd card after every chunk). 

Should be simple enough to adjust for some power down mechanism (and maybe add a button to manually sync data before removing sd card)...

 

#include <SoftwareSerial.h>
#include <SD.h>

char buffer[100];
int buffer_pos = 0;
uint8_t sdavail;

#define CurrentBaudrate 115200

SoftwareSerial softSerial = SoftwareSerial(5, 4, false);

void setup() {
	sdavail = SD.begin(SDC_CS);
	
	setupScreen();

	Serial.begin(CurrentBaudrate);
	softSerial.begin(CurrentBaudrate);
	softSerial.listen();
}



uint32_t lastTouched = millis();
char msg;

void loop() {
	while (Serial.available() || softSerial.available()) {
		msg = Serial.available() ? (char)Serial.read() : (char)softSerial.read();

		buffer[buffer_pos++] = msg;
		
		if (buffer_pos >= sizeof(buffer)) break;
	}

	if (msg == '\n' || buffer_pos >= sizeof(buffer))
	{
		writeBuffer();
	}

}

void writeBuffer() {
	if (sdavail) {
		File dataFile = SD.open("datalog.txt", FILE_WRITE);
		if (dataFile) {
			dataFile.write(buffer, buffer_pos);
			dataFile.close();
		}
	}
	 
	buffer_pos = 0;
}

 

[johanvdw]

I communicate to the device using modbus, not direct rs232. The main reason I'd prefer a non-arduino solution is that I have the code working and tested on linux.

Checking out arduino nevertheless, as it would probably be a better solution on the longer term.