Raspberry Pi Forums

I am new at Raspberry and Python, so I will be very glad if you help me at my problem. I need to read some data from weight scale when button on scale is pressed. When I connected this scale via USB on PC, I saw that it works as HID. When I press the button, data are written as string in some text edit document for example.
So, now I am going to connect this scale on Raspberry Pi to read and manipulate with data. Can you give me some code example, advice, which library I need to import? I want to write a script, that waits for incomming data and then something do with it. Thanks for help.

What happens when you plug it into a Pi and press a button?

Hi,

anze87 wrote:data are written as string in some text edit document for example.

It seems that the weight scale represents itself as a standard HID keyboard.

In order to read its output, your software needs have focus and you read data 100% equally as when you type the values on your keyboard.


Best wishes, Ivan Zilic.

I finaly find time to moving forward. I try to read data, and it works just like from keyboard.
This works: I also try like this, but failed: I don't know why incomming data are different in win8 and in Linux. For example, in Win I get string "G + 12.34 g" in Linux just "1234 ". When I read string data, I remove whitespaces with split() method, so I get just "1234". Because scale has fixed two decimal numbers, it's not a problem to divide with 100. But it becomes a problem, when result from weight is negative, and I can't know that. Does anybody know, what could be the reason for that? The result is the same, if I just open text editor and press button on scale, so I don't think it is problem in reading...

Thanks!

Usually when a weight comes up negative, it means that it is either in overload, there was a weight on the scale when it was powered up (tare weight) , or there is an error. Try power cycling the scale with nothing on it and see if the negative values go away.

Yes, I understand that. But I can't figure it out why in Win is received data different than in my Raspberry. In Win I get sign (+) or (-) and decimal dot (.) and unit (g). In Raspberry I get just numbers and spaces after numbers, without anything. What would cause that, any ideas to check?

Hi,

anze87 wrote:What would cause that, any ideas to check?

Weird... I first thought about NumLock,... but this doesn't explain behavior well...
Do you have a chance to sniff USB communication ?


Best wishes, Ivan Zilic.

Do you mean with some kind of software? Isn't USB very complex protocol?

Hi,

anze87 wrote:Do you mean with some kind of software? Isn't USB very complex protocol?

There are also some software-only sniffers. Since I worked with hardware-based only so far, I cannot write much about these software tools... Anyway, check this: http://biot.com/blog/usb-sniffing-on-linux


Best wishes, Ivan Zilic.

It was very stupid problem. I had wrong keyboard emulation settings on scale. Now it works, as it should. Thanks for help!

I'm interested in using the Pi to read scales, could you tell me what scales you used?

Regards
Lee

Hello,
some time ago I connected a barcode scanner to raspberry, using my python scratchClient software and scratch.
I wanted to avoid the problem, that HID input is accepted only when the program runs in foreground.
http://heppg.de/ikg/wordpress/?p=390
Although the target here is to connect this to scratch, the python code is straightforward and you find it in scratchClient/src/adapter/usbAdapter.py

Regards,
Gerhard