PLUS+1 Hardware > Controllers

12V external pull-up

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spittet:
Hi,

I have a MC050 with a MFIN input that I would like to add a +12V external pull-up resistor. The PinConfig is already set at "Activate w/ ground" "pull-up to internal 5V" because the input signal will be a ground when activated. Would there be any conflict between the external +12V pull-up resistor and the +5V internal pull-up resistor, hardware side?

I tried it on my MC050 and I was able to make it work correctly with a 4.7k external +12V pull-up resistor, so I know it can be done and it can work OK. My question is more about may I break something in the long term on this input pin doing it this way?

Have a good day!

Marbek_Elektronik:
What is the voltage you get on the Pin with this 2 resistors to 12V and to 5V? 11V?

Why do you not use "Bias: 0 = DigIn activated with Sourcing Power"   ?
And then negate the signal?
And use an external pull up to 12V?

Range 1?
DigThresHigh: 4500mV   Low 3500mV?

spittet:

--- Quote from: Marbek_Elektronik on October 14, 2020, 09:31:44 PM ---What is the voltage you get on the Pin with this 2 resistors to 12V and to 5V? 11V?

Why do you not use "Bias: 0 = DigIn activated with Sourcing Power"   ?
And then negate the signal?
And use an external pull up to 12V?

Range 1?
DigThresHigh: 4500mV   Low 3500mV?

--- End quote ---

Yeah, I got about 10.3V for a 12.2V source.

I was looking for a solution where only the harness would need to be touched and not the program. That's the reason why I wanted to keed the program side the same/untouched.

Still looking for an answer about if this could cause long-term problems.

Marbek_Elektronik:
Ok, I understand.
So, you have (12,2V -10,3V) / 4700 Ohm = 0,4 mA to Controller-pin, if your switch is open, no connection to ground.
In case of your pin configuration, the controller switches a resistor Rx to 5V and a resistor Rx to 0V and you get 2,5V at the pin, if it is open.

So, the 0,4mA flows from 10,3V to 5V and to 0V. Theoretically you have 1/3 from 0,4mA to 5V power supply = 0,13mA.

I don't think, this damage anything. Resistor from 5V to output is about (10,3V-2,5V)/0,4mA*2=39000 Ohm.

Only danfoss devoloper can tell you if it is OK to do so. But, I think, it is OK.

Tor:
Hi,

I don't think this should be a problem since the MF input can handle 36V.
But to be sure I have sent the question to a Hardware developer. I hope they don't have to much to do, and have the time to answer.

I'll get back to you.

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