[Nut-upsuser] NUT and relay on USB

Charles Lepple clepple at gmail.com
Tue Jan 20 12:38:09 UTC 2015

On Jan 20, 2015, at 4:39 AM, Maurizio <maurizio.iacaruso at gmail.com> wrote:

> Hi there,
> I have a question about a raspberry pi as NUT server and a "relay".
> I explain my situation: I have an UPS with USB port, so I connect it to 
> the rasp. The problem is that I have a device manageable only via USB 
> port.
> How can I handle this configuration?
> My assumptions are:
> 1) split the USB cable from UPS to rasp and device, but I don't know if it 
> works

As Manuel mentioned, you will need a USB hub. It will work better with an external power supply for the hub.

However, if you don't already have a hub, you may want to consider a Raspberry Pi Model B or B+, with 2 or 4 ports, respectively.

> 2) connect the UPS to rasp directly, so connect the rasp (by GPIO) to 
> device as a Serial port with a DIY cable.
> The problem with second solution is that I don't know if (and how) I can 
> do it with NUT.

I don't think anyone has tried connecting to the serial port on the RPi expansion header, but NUT should not have a problem (as long as the driver is not expecting flow control pins). However, the serial port is TTL levels, so you would need a TTL-to-RS-232 level shifter chip. The USB hub would be a lot simpler, IMHO. 

Charles Lepple
clepple at gmail

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