Kogna disconnects from PC after Bit is set high

[TFrenken]

Greetings,

I have a problem after updating to Kmotion 5.4.1. When I switch Bit 255 or 256 ON, Kogna disconnects immediately from the PC. The Bits are activated but there is no way to reconnect without restarting Kogna. Both Bits are used as General Outputs and drive small solid-state relays. There seems to be no problem with Bit 254 which uses the same relays. This problem does only occur on this machine and not on the others where I use the same hardware setup. Before I updated the software, I used Bit 255 and 256 very often as they activate the tool change and coolant respectively. I do remember having this problem with Bit 256 maybe 2 or 3 times one day but since then it has worked for many months without it happening.

I did use a resistor in line with the relays to limit the current in case the activation of the relay triggers a safety feature on Kogna and also changed the relays. When switching the bits without load attached (JP10 disconnected) the problem does not occur.

Could this be a problem because of the update to 5.4.1. or is the board defective?

Regards,
Thomas

[TomKerekes]

Hi Thomas,

How is Kogna being powered?

What type of Solid State Relay is it? How is it wired?

If the outputs of the relays are disconnected does the problem still occur?

How are the bits being activated? KMotion’s Digital IO Screen?

Have you checked the JP10 cable/wiring for shorts?

[TFrenken]

Hi Tom,
thanks for the quick reply.
Kogna is powered by a Meanwell 5V 3A power supply.

I use SSR-41FDA Solid State Relays, as with my other boards. The positive input is provided by the Bit and the ground ia connected to the ground of the power supply. Could it be that the power supply ground differs from kognas digital ground?

I switched to other relays in the cabinet without connecting the outputs and it occurs as well. As I said I do not have problems with my other Kogna boards or the other Bits of this board while using this relays.

The problem happens whether I use the IO Screen or activate it with a button oder C Programm.

I checked the breakout board of JP10 for shorts and found none. I ruled out the cable as the problem does not happen when the cable is not connected and the problem occurred without changes to the wiring of the cabinet. But I will check the cable as well.

[TomKerekes]

Hi Thomas,

I couldn’t find a specification on the SSR but it’s hard to imagine its input would be an issue. Although some images I found show an LED with no resistance. What value resistor did you add?

Grounding back to the 5V supply should be ok. The grounds on Kogna are all common. Although possibly a big loop. Another option might be to connect back to Kogna or to the - differential output.

To be clear I understand you somehow connect a different SSR with nothing connected to its output and it still fails?

Can you try another Kogna? A previous software version? I can’t think of any changes that would be related.

[TFrenken]

Hi Tom,

I did a few tests on the weekend and found the cause of the problem. If I understand correctly the problem should have been the high power consumption of the internal 3.3V supply. The Home and Limit Switches(Bit 200 - 203 JP9) used the 3.3V supply and the Limits are always on. After disconnecting the 3.3V supply the Bits on JP10 work fine. However using resistors with the internal 3.3V to power the Limit and Home switches doesn't seem to work. There should be internal resistors on the Bits 200-207 so external resistors should not be needed, right? Do Bit 208 and 209 not have an internal resistors?
Could I use the 5V supply with a bigger resistor to drive 3.3V IO Bits? What is the minimum switching voltage for these?

Is there something of an error log for Kogna? The board was still running after disconnecting (even running the homing C Program if I activate the bit during homing). So maybe there is a way to get more information if a problem occurs.

[TomKerekes]

Hi Thomas,

Kogna's 3.3V regulator is rated for 1.6A and should shut down at 1.9A.

The first 8 of 10 Aux inputs have 150 Ohm pull down resistors. So pulling those inputs up to 3.3V would consume 22ma each. I'm surprised that extra load causes a problem. But I suppose if there is enough devices and IO to be on the threshold that could explain this.

However using resistors with the internal 3.3V to power the Limit and Home switches doesn't seem to work.

What resistance did you try?

The input threshold for a high needs to be 2V but I'd recommend 2.5V for noise margin.

So connecting the input to 5V though a 150 Ohm external series resistor (to pins with a 150 Ohm pull down) should pull the pin to 2.5V

There should be internal resistors on the Bits 200-207 so external resistors should not be needed, right?

I'm not sure what you mean. These have 150 Ohm pull down resistor to GND. Connecting to 5V without an external series resistance would cause damage. The absolute maximum voltage on the inputs is 4.1V

Do Bit 208 and 209 not have an internal resistors?

They do not.

Is there something of an error log for Kogna? The board was still running after disconnecting (even running the homing C Program if I activate the bit during homing). So maybe there is a way to get more information if a problem occurs.

I suspect if it is a 3.3V dropping issue the Ethernet Transiver is more sensitive than the DSP so Ethernet is lost first. You might monitor Kogna's UART messages to the PC COM port for any clues such as Loss of Link.

HTH

[TFrenken]

Hi Tom,

thank you for your help and suggestions. I found the JP9 connector to be the cause of the disconnect problem.
I also changed the system to lower the power needed of the 3.3V supply and now use the internal 3.3V through low power electro-mechanical relays on JP9 as Inputs(JP9 3.3V -> relay ->JP9). The 5V for Kogna and 24V cabinet voltage use the main(400V) ground as a common ground. Apart from the IDE cables to kogna all signal wires are shielded to the same main ground. The problem of disconnecting from the PC only occurs if JP9 is plugged in and I start a 400V hydraulic system for the tool change. It does not matter if I activate the 400V relay manually or with a switch or by an Output from Kogna. I did change the kogna to a newer one but there was no change in the situation. This only occurs with the JP9, the other connectors in the system JP5, JP7,JP8, JP10 and JP14 do not cause problems. As I like to use specific connectors for the different tasks and keep it consistent with the other machines I would like to be able to use JP9.
As the hydraulic pump uses a standard 3 phase asynchronous motor i do not see how this could cause the problem. Other 3 phase motors are used for lubrication and ventilation on parts of the machine and do not cause problems when turned on.

I would be glad if you have any suggestions about the cause of this problem with JP9 and how to solve it. So far Kogna is a very stable and highly performant control for my machines and I really like using it.

As a side note I would really like to have an upgraded version of KmotionCNC with modern looks, all the standard features(like probing, etc.) and configurability as a paid option. The software is so capable but for users like me a clean modern look would be much appreciated.

[TomKerekes]

Regarding mechanical relays: they cannot usually be driven by LVTTL signals. What are their specifications and do they have a reverse diode across the coil?

Regarding 400V ground. Is this earth ground? It doesn’t normally make sense to connect a noisy earth ground to shields of signal lines.

You might try to determine if noise is picked up on the JP9 cable and causing problems with Kogna’s reset signal. Try making a cut of the pin 4 reset wire right at the Kogna connector.

[TFrenken]

Thanks for the quick reply.
The relays are driven by 24V signals and only switch the LVTTL signals to the internal 3.3V. This seems to work better than using solid state/ opto relays for input isolation.
For outputs I do use solid state relays or special mechanical relays rated at 3V which work fine.

Yes the 400V ground is earth ground in this system. I reworked the grounding of the cabinet, as it was my first retrofit it was kind of sloppy before.
I have also cut the cable to PIN4 of JP9 and now it seems to work without problems. I will definitely keep an eye on noise reduction on the next retrofits.

Thank you for the great support!