Pump failed to stop

[basanlab]

Hello,
We have two chi bio setup ( one runs 8 reactors, another runs 1 reactor). In the setup with single pump, and single reactor, I have noticed a problem that in OD regulation mode, both pumps are turning on and failed to stop. Somehow the pump feedback is not working. Please let me know your suggestions.
Another question is about a message that I am getting sometime : “Failed pump coms ‘n’ times on device M(n), if this error persists more than 10 times, then the entire system shuts dowm. Any suggestion how to avoid this?
Another error message I get is ‘Failed Multiplexer Comms ‘n’ times’ , I guess if this error persists certain number of times, the device shuts down. How can I avoid this problem.
Please let me know your valuable suggestions.
Best,
Avik

[harrison]

Hi Avik,
Have you got the most recent software installed?
In particular, on this page: https://chi.bio/software/ there is a new Software V2.0 setup guide which should fix this.
The issue is probably that with your current software version it can take a while to recover from some communication issues. The updated software fixes this by updating the Linux Kernel to change how it handles communications errors.
Let me know how it goes!

[basanlab]

Hello Harrison,
Thanks a lot for your reply and suggestion. I have flashed both our chi-bio set up with Version 2 of the software, and pumps are working stable. But while troubleshooting this problem, I have noticed something very interesting. Chibio came with small micro USB cables, to connect the control computer with the reactor and reactor with pump.
For our convenience with too many reactors, we connected the connected the control computer with each reactor with 3 meter micro USB cable, and another 3 meter micro USB cable that connects each reactor with its cognate pump.
I realized these two long cables, causing the pump failure. I have tested a few configurations, as mentioned below.
(1)Control computer–>short blue cable–>reactor–>short blue cable–>pump : perfectly works
(2)Control computer–>LONG 3M cable–>reactor–>short blue cable–>pump : perfectly works
(3)Control computer–>LONG 3M cable–>reactor–>LONG 3M cable–>pump : Pump communication problem (even after software update).
Presently I am running the set up as mentioned in configuration(2). I will be most grateful, to receive your valuable comments on this.
Best regards,
Avik

[harrison]

Hi Avik,
I am not too surprised by this. The problem is that the digital communications (which use I2C protocol) are sensitive to the capacitance of the connection (i.e. wires) between the differnt components. The longer cable has more capacitance (there is more copper there – so it takes longer for the system to drive the digital signal high/low) and hence the digital signal has slower rise/fall time when the longer cable is used. When the cable is TOO long this rise time becomes too slow, meaning the chip on the pump is unable to “see” the digital signal properly – it gets corrupted.

I think in later versions of the device we will work out additional mechanisms for buffering this connection so that it is possible to reliably use longer cables on the pump side. But for now it seems sensitive to very long connections (though the software does make it a bit more robust in some cases).

[basanlab]

Hello Harrison,
Thanks a lot for explaining this. Will it be ok, if I use long cable to connect the control computer with reactors and then short cable to connect the pumps, as I am doing presently(mentioned in configuration 2)? Please let me know your suggestion on this. Or I should totally avoid long cable, for more stability.
I will be most grateful to receive your suggestions.
With best regards,
Avik

[harrison]

I think whatever works, works! If you want to have a long cable in there and it seems happy with it then go with that.

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