Dynomotion

Group: DynoMotion Message: 7830 From: aguskov1987 Date: 6/30/2013
Subject: Problems with input pins
Hello, everybody.
I am using kflop to control a small hobby cnc machine. Everything looked fine until I started setting up homing switches.
The switches are simple mechanical sensor with two connectors. I connected one to the 3.3v and the other one to the input pin. The problem is that I can basically trigger the input pin by touching it with a screwdriver. I also see that when I apply voltage to the input pin, the neighboring pin also goes active. It looks really weired. I have a feeling that I am not grounding the board properly. I have the ground via connected to the metal frame. Is there another ground I should take care of?

I don't really understand how I can trigger an input with a piece of metal with no voltage applied. Shouldn't they only read if they have 3v applied to them.
Any ideas?
Thank you, everybody
Group: DynoMotion Message: 7831 From: Tom Kerekes Date: 6/30/2013
Subject: Re: Problems with input pins
Hi Agustov,

The KFLOP inputs are high impedance (meghohms) mosfets.   They can float high or low with almost zero current.  You must drive them high and low for them to work properly.  An unused floating input will often follow a neighboring pin due to parasitic capacitance.  This is normal.  Add a 1K ohm pull down resistor to ground so that when the switch is open the pin will be pulled to zero volts by the resistor and not just be floating.

Some of the KFLOP inputs (the first 8 on JP4 and JP6) have internal 150 ohm pull down resistors so you might use those.  The pins on JP7 marked for Home inputs are just default recommendations.  Any input can actually be used.

Grounding is very complex.  Please do some research on the subject.  You probably do not want the KFLOP DC ground connected to the frame of the machine.  The frame of the Machine is likely to be a very noisy earth ground.  And sice the DC Ground is probably tied to Earth GND somewhere else this creates what is called a ground loop.

Regards
TK

Group: DynoMotion Message: 7833 From: Steve Date: 7/1/2013
Subject: Re: Problems with input pins

FWIW, I ended up making an all new interface board based on an old 4050N based board that I made up a few years back for a DC drive with a weak alarm signal.

I was unable to modify my normal 24V isolated interface board enouigh for the Kflops pulled down pins, so I resurrected an older 4050N based board that I made a few yaears ago for use with a DC drive that had a very weak alarm signal.  It worked with the Kflop and I had three of them lying around so I was able to get things going.

www.thecubestudio.com/theROCKp roject/SensorInterfaceBoardsTe mporaryInstalledWEB.jpg

Ultimately I had to design/build/test an all new board that accommodated all 6 axis, had caps on the Kflop pins, pull downs on the 24V signals, LED indicators for each channel and built to my (now standardized)  mounting dimensions. It is a simple little board and although it has only a short amount of run time, the board seems to be stable so far. It draws a little over 5mA from teh 24V Optical switch signals and provides 13.9 mA to the hungry Kflop input pins.

www.thecubestudio.com/theROCKp roject/ MultiLineInterfaceTopFront1WEB .jpg

This new board is now permanently installed with its siblings in a rather complex setup needed to interface the Kflop with various systems.

www.thecubestudio.com/theROCKp roject/ElectronicsRevisedComme ntedWEB.jpg

To offer an unsolicited opinion;  those pull downs should be on the daughter card that needs them instead of on the main board where they are a PIA to deal with. The delivery date for this machine is too close to consider rewiring, but it seems like the best solution would be to use the pulled down pins as outputs and reserve the 'normal' pins for input . . . . . as much as possible.

- Steve

 

 

 

--- In DynoMotion@yahoogroups.com, Tom Kerekes wrote:
>
> Hi Agustov,
>
> The KFLOP inputs are high impedance (meghohms) mosfets.   They can float high or low with almost zero current.  You must drive them high and low for them to work properly.  An unused floating input will often follow a neighboring pin due to parasitic capacitance.  This is normal.  Add a 1K ohm pull down resistor to ground so that when the switch is open the pin will be pulled to zero volts by the resistor and not just be floating.
>
> Some of the KFLOP inputs (the first 8 on JP4 and JP6) have internal 150 ohm pull down resistors so you might use those.  The pins on JP7 marked for Home inputs are just default recommendations.  Any input can actually be used.
>
> Grounding is very complex.  Please do some research on the subject.  You probably do not want the KFLOP DC ground connected to the frame of the machine.  The frame of the Machine is likely to be a very noisy earth ground.  And sice the DC Ground is probably tied to Earth GND somewhere else this creates what is called a ground loop.
>
> Regards
> TK
>
>
>
> ________________________________
> From: aguskov1987 aguskov1987@...
> To: DynoMotion@yahoogroups.com
> Sent: Sunday, June 30, 2013 7:13 PM
> Subject: [DynoMotion] Problems with input pins
>
>
>
>  
> Hello, everybody.
> I am using kflop to control a small hobby cnc machine. Everything looked fine until I started setting up homing switches.
> The switches are simple mechanical sensor with two connectors. I connected one to the 3.3v and the other one to the input pin. The problem is that I can basically trigger the input pin by touching it with a screwdriver. I also see that when I apply voltage to the input pin, the neighboring pin also goes active. It looks really weired. I have a feeling that I am not grounding the board properly. I have the ground via connected to the metal frame. Is there another ground I should take care of?
>
> I don't really understand how I can trigger an input with a piece of metal with no voltage applied. Shouldn't they only read if they have 3v applied to them.
> Any ideas?
> Thank you, everybody
>