Using Analog Input AUX

Printable View

03-06-2022, 10:35 AM
awpross

Using Analog Input AUX

The MK3 is equipped with analog inputs, but I have some problems using them.

I know it is easy to use a poti, connected to GND and 3,3V and connect it to AUX2 for example. But in my situation I have a infrared temparature sensor which has an analog output 0-10V.

So i thougt would be easy: Using two resistors to create a voltage divider between the 0-10V signal and GND to get an voltage output of 0-3.3, but it looks like I have some problems with the voltage reference and even if i directly connect the 0-10v to AUX, i can not use the full range of the AUX input.

Measured to ground I have had 3.3v on the AUX, but the display showed only a low value. Connecting the AUX to the onboar 3.3v, it shows maximum value. That's why i think the AUX may have a internal voltage reference which is not directly related to the GND or the Infrared sensors 0-10V output has some unknown behavior.

Is somebody using the AUX in for 0-10V measurement and can suggest how to connect it properly?
03-06-2022, 01:06 PM
dazp1976

Quote:

Originally Posted by awpross

The MK3 is equipped with analog inputs, but I have some problems using them.
I know it is easy to use a poti, connected to GND and 3,3V and connect it to AUX2 for example. But in my situation I have a infrared temparature sensor which has an analog output 0-10V.
So i thougt would be easy: Using two resistors to create a voltage divider between the 0-10V signal and GND to get an voltage output of 0-3.3, but it looks like I have some problems with the voltage reference and even if i directly connect the 0-10v to AUX, i can not use the full range of the AUX input.
Measured to ground I have had 3.3v on the AUX, but the display showed only a low value. Connecting the AUX to the onboar 3.3v, it shows maximum value. That's why i think the AUX may have a internal voltage reference which is not directly related to the GND or the Infrared sensors 0-10V output has some unknown behavior.
Is somebody using the AUX in for 0-10V measurement and can suggest how to connect it properly?

Well. The user manual states:
AUX connector is "reserved for future use".
Whatever that means.

You may need to look at the EXT/in and EXT/out expansion boards for the EXT headers not AUX.
03-06-2022, 04:03 PM
awpross

Re: Using Analog Input AUX

The user manual has not been updated since 2014.. the mk3 controller has menawhile 2 red ext connectors and 1 red canbus adapter with two jumpers which has nothing to do with the manual from 2014...
So the "future use..." on aux connector is outdated

The Ext in and Ext out does not support analog. But the aux connector does.

The documentation is just behind the actual progress of the MK3 Hard and Software... Personally, i miss detailed descriptions of the connections, but I understand that problem. I am a software develloper and I know the problem of beeing behind with documentation.
Especially the in and outputs are rarely documented and the existing descriptions are just covering the very basic connections.
03-06-2022, 04:04 PM
PlanetCNC

Re: Using Analog Input AUX

"reserved for future use" means, that we planned add-on board for this (analog joystick) but then we decided on different solution.
Be careful because these pins are not protected and main processor can be easily damaged.
03-06-2022, 04:15 PM
dazp1976

Quote:

Originally Posted by PlanetCNC

"reserved for future use" means, that we planned add-on board for this (analog joystick) but then we decided on different solution.
Be careful because these pins are not protected and main processor can be easily damaged.

Sort your documentation please.
Many scrutinise pdf docs before deciding on hardware selection.
So called "2 analoge inputs" are non existent and any wiring "mishaps" should be on planetcnc's head.

Every other non planetcnc controller I look at have issued up to date revisions on a regular basis.
03-07-2022, 10:46 AM
awpross

Re: Using Analog Input AUX

Quote:

Originally Posted by PlanetCNC

"reserved for future use" means, that we planned add-on board for this (analog joystick) but then we decided on different solution.
Be careful because these pins are not protected and main processor can be easily damaged.

Sounds like a good idea to provide any infos to use the aux connector for analog input and develop an ad on board which adds safe support for analog input.
common analog input would be 0-5V / 0-10V / 4-20mA

I do not have any experience with optocouplers but i am sure with the right knowledgement it would be possible to use it for isolation of the analog input. It may not be required to have perfect linearity, that could sure be compensated internally by scripts.

I already found a good circuit example which was originally designed for arduino but thats not a module who could be bought somewhere: https://www.electronics-lab.com/proj...le-for-arduino
I don't know how to rebuild the example. Seems to be expensive for a single piece.. maybe it could be adapted to the MK3 and then provided as addon for MK3??
03-14-2022, 10:29 PM
awpross

1 Attachment(s)

Re: Using Analog Input AUX

Do You think the attached circuit may be sufficient to protect the analog Input?

I have no knowledge of the internal circuit of the MK3s AUX IN, so this is very theoretically..

The shotkey diods are for preventing lower than GND and higher than 3.3V ref. Found that on some examples. With that, the max voltage would be aprox 3.6 Volts and the lowest -0.3V caused by the shotkey voltage drop.
The 10nF capacitor should smothen the signal.
The 10k resistor should reduce current in case of over or under-voltage.

In case of over-voltage. For example 24V directly on the 0-10V output, the max current through 3.3V connector should not exceed -0.5mA with that circuit. Don't know if MK3 can handle that but seems better than having 8V on AUX IN in case of miss wiring.

Don't know if the GND of AUX connector is the same than GND of the Power Supply of the MK3.
06-11-2022, 04:19 PM
awpross

1 Attachment(s)

Re: Using Analog Input AUX

I have now a working solution for using AUX as Analog Input.

It's not the cheapest solution, but industrial style with a 3-way isolated Signal converter like Weidmüller EPAK-VI-VO 7760054175
There are different converters available for 4-20mA and 0-10V

The Output is fully isolated and directly supplies 0-10V. With a simple voltage devider, it could be used as 0-3.3V for the AUX input.

Because of the 3-way isolation, powersupply is also isolated from input. So you can adapt the input to different situations.
There is no additional protection of the AUX input necessary because the output is already limited, filtered and protects the output up to 2500 Volts on input or powersupply.