cawy7

Grounding/Common Issue

Recommended Posts

Hello! I've been having a mystifying issue and was hoping someone would be able to help.

I have been fiddling with a WF32 project involving a barcode communicating over serial and a quadrature rotary encoder 200 P/R.

I am unable to run both at the same time right now.

I am running the encoder and barcode scanner from a 12VDC Battery, the encoder is open collector so because the WF32 has no internal pull-up resistors on most digital pins, I have made my own using about 18k resistors. 

The WF32 is being powered over UART right now, although I have tried to tie it into a 5VDC power supply with no luck.

TX/RX from the barcode scanner is going to PIN 39/40 on the WF32, Can communicate when the common is disconnected from the 12VDC common

Encoder signals are going to PIN 8/9, Will work when the common is connected to the 12VDC common 

Here is the basic circuit (I couldn't find proper components in fritzig at all so I made do with some ms paint haha).  The red circle is the issue, if I connect it I get encoder but not barcode, vice versa if I remove it.

 

Would be happy to share more if more information is needed.

WF32-Added.thumb.png.d1ca2d8e1541c060ac493a2f457b5e8c.png

 

 

Share this post


Link to post
Share on other sites

Hi @cawy7,

I don't know if I am mis-seeing this, but on your encoder, is the ground line connected to the 12V line up at the top of the encoder? I presume that's not the case since you would likely notice it in the form of heat, but I'd figure I'd check anyway. Can you link the datasheet to the barcode reader so I can better understand what they mean by DC+ and DC-?

Thanks,
JColvin

Share this post


Link to post
Share on other sites

Yeah, there were no good drawings for how the encoder is actually set up, the ground is going to the ground of the encoder, it's just not shown. 

Here is the link for the Barcode reader:

http://eola.cz/images/cognex/download/DM70-Reference-Manual.pdf

Specifically I am using the cable on page 8, Pin 4 on the cable is connected to the common, Pin 5 to positive. I've attempted to connect the output common also and it hasn't Changed the situation.

 

I'm currently still working on it and I've isolated it to just the barcode reader as I was attempting to make progress by just flipping grounds when I need each device. After some time I needed to charge the battery (portable multiple voltage device charger (https://www.amazon.com/Crave-PowerPack-CRVPP101-Ultra-High-Portable/dp/B01BLXY3B6), that resulted in the barcode scanner not working again. So, i've disconnected the encoder all together and I'm able to replicate the same thing by plugging in the charger for the battery to the wall. I have a fused switch on the hot side of the plug-in so even if the switch is off and the battery is not charging (but plugged in) I can't get signals. I tried tying all the ground together again, thinking a true earth ground would help. But, again the problem continues.

Share this post


Link to post
Share on other sites
On 9/26/2018 at 2:12 PM, JColvin said:

Hi @cawy7,

I don't know if I am mis-seeing this, but on your encoder, is the ground line connected to the 12V line up at the top of the encoder? I presume that's not the case since you would likely notice it in the form of heat, but I'd figure I'd check anyway. Can you link the datasheet to the barcode reader so I can better understand what they mean by DC+ and DC-?

Thanks,
JColvin

@JColvin  So after extensive testing the only thing we can come up with is that I need to use something like:

https://reference.digilentinc.com/reference/pmod/pmodrs232/start

 

It appears to be some sort of issue where it will only read the serial when the ground is floating. We suspect that there are some things we don't know about going on and the only thing we can think of is that the external 232 serial needs to be converted to TTL serial as most other projects doing something like this are doing that.

Share this post


Link to post
Share on other sites

Final update to anyone who uses this as a reference. The Pmodrs232 worked, so it must of been some sort of ground reference issue.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now