grnd4sat
Posts: 14
Joined: Tue Jan 08, 2019 3:07 pm
Location: Turin (Italy)

ribbon connections

Sat Jan 19, 2019 12:08 pm

Hy everyone/anyone.
I had some troubles connecting GPIO pins via a ribbon. I'm now checking my ribbon by means of a multimeter, connecting the 3V3 pin of the Pi to a plug on the ribbon. With one lead of the multimeter directly connected to a ground pin on the Pi, I would check the pins out of ribbon one by one to find the 3V3 voltage.
I expected to find only one pin with 3V3 power, but surprisingly I get a number of pins with that power on.
Is my ribbon faulted? Or maybe I just don't understand the rationale of connections?
I wish I could attach a pic, but still the file is too large...ok, managing...
ribbon miniat1.png
ribbon connected to Pi & multimeter
ribbon miniat1.png (113.05 KiB) Viewed 212 times
done..
Thanks a lot ...

pcmanbob
Posts: 5046
Joined: Fri May 31, 2013 9:28 pm
Location: Mansfield UK

Re: ribbon connections

Sat Jan 19, 2019 12:39 pm

Looking at your picture the pi in the background looks like a pi 1 with 26 pin gpio, you you look to be using a 40pin gpio extender, which I dont think you will get to physically fit on the pi in the correct position to line up the gpio pins.

Try posting so better pictures, upload them to imgur.com and post links to them in your post.
Remember we want information.......................no information no help
The use of crystal balls & mind reading is not supported

grnd4sat
Posts: 14
Joined: Tue Jan 08, 2019 3:07 pm
Location: Turin (Italy)

Re: ribbon connections

Sat Jan 19, 2019 2:43 pm

...I actually do not know the Pi model I am currently using...it is an old version and yes it's 26 pis.
I bought a ribbon but didn't pay attention to the number of pins, and its actually a 40 pins ribbon.
I checked which pin matches which plug with a multimeter and finally I connected the ribbon using only the 26 holes on one side...
I know it would be easier to get 5 euros and go shopping in a computer store....but what's the fun of it?
Oh, thanks for the idea of Imgur!!!
https://imgur.com/a/v7kIFoN

User avatar
rpiMike
Posts: 657
Joined: Fri Aug 10, 2012 12:38 pm
Location: Cumbria, UK

Re: ribbon connections

Sat Jan 19, 2019 3:47 pm

What have you got connected to the other end of the ribbon cable? If you are testing the cable you should have nothing connected except for your test leads!

grnd4sat
Posts: 14
Joined: Tue Jan 08, 2019 3:07 pm
Location: Turin (Italy)

Re: ribbon connections

Sat Jan 19, 2019 4:30 pm

Thanks rpiMike.
You are right...If I want to detect faults on the Ribbon, I have to check the ribbon only...What you see at the end of the ribbon is a socket that returns female ribbon plugs to male pins, as far as I know. But I now find out that some of the female pins on one side of the ribbon are replicated on same pins of the socket.
I think I have connected the socket on the wrong side of the ribbon....

drgeoff
Posts: 8978
Joined: Wed Jan 25, 2012 6:39 pm

Re: ribbon connections

Sat Jan 19, 2019 4:49 pm

The cobbler (the T-shaped thing) replicates the RPi GPIO header. The GPIO header does have some sets of commoned pins, eg ground and power rails are on more than a single pin. So I would expect that some pins on the cobbler are commoned. See https://raspi.tv/wp-content/uploads/201 ... inouts.png

grnd4sat
Posts: 14
Joined: Tue Jan 08, 2019 3:07 pm
Location: Turin (Italy)

Re: ribbon connections

Sat Jan 19, 2019 5:39 pm

Thank you drgeoff.
I am checking ribbon+ cobbler disconnected from the Pi. I power one plug on the ribbon with a 8V battery and check the cobbler pins for that voltage with a multimeter.
The point is that if I power, say, plug #1, I get those 8V on pins #5 and #13 of the cobbler. if I have 40 pins on cobbler and 40 pins on ribbon, well I expect a unique match...

https://imgur.com/a/pKedGRi

User avatar
rpdom
Posts: 13389
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: ribbon connections

Sat Jan 19, 2019 6:00 pm

grnd4sat wrote:
Sat Jan 19, 2019 5:39 pm
The point is that if I power, say, plug #1, I get those 8V on pins #5 and #13 of the cobbler.
The Cobbler board will connect all of the GND pins together, both of the 5V pins together and both 3.3V pins together.

Try checking the cable without the Cobbler connected.

grnd4sat
Posts: 14
Joined: Tue Jan 08, 2019 3:07 pm
Location: Turin (Italy)

Re: ribbon connections

Sat Jan 19, 2019 6:25 pm

Got it!
Thank you drgeoff and rpdom! Thank you all.
I did not consider these connections, now I see more clearly why I had those strange behavior of my circuit.
I plugged the ribbon to the 26 pins array on the Pi, and it would work if I didn't use the cobbler too. ..But I did use the cobbler and that is suited for a 40 pins array, connecting together pins with same function...If you add the fact that I plugged the ribbon matching its 39 and 40 plugs on pins 25 and 26 of the Pi...I let you imagine what a chaos!!!

...it's lovely to find out there is a rationale where I thought it was all chaos!

Return to “Troubleshooting”