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Home/Forums/T7/ Disconnect the pull up resistors in the digital inputs
Disconnect the pull up resistors in the digital inputs
To remove the pull-up resistors I need the schematics or the layout to be able to identify the resistors that I need to remove when I open the Labjack. Could you provide me this information?
I see you sent an email also, and someone will respond to that with the details you need. Here on this topic, let us know more about why you want no pull-ups and we might have alternative ideas.
1. When your signal is in condition A, you need to hold the T7 digital input low. This is normally done externally by adding a pull-down resistor (4.7k is typical) that overpowers the internal pull-up. See the Open-Collector Signals App Note. Other options are the LJTick-Divider or RB12.
2. When your signal is in condition B, you need to protect the digital input from the high voltage. Per the Driven Signals App Note, you can do that with a series resistor, or the LJTick-Divider or RB12 are great options.
I would suggest that the LJTD-5 takes care of both issues for you.
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Hello,
The only resistors that could get removed are the internal pull-up resistors unless you have installed some of your own.
Hi,
To remove the pull-up resistors I need the schematics or the layout to be able to identify the resistors that I need to remove when I open the Labjack. Could you provide me this information?
I see you sent an email also, and someone will respond to that with the details you need. Here on this topic, let us know more about why you want no pull-ups and we might have alternative ideas.
So it sounds like you have PNP signals, where the signal has 2 states:
A. High-Impedance or Open
B. Driven 24V
Does that sound right?
https://labjack.com/support/app-notes/open-collector-signals
So this would suggest you need 2 things:
1. When your signal is in condition A, you need to hold the T7 digital input low. This is normally done externally by adding a pull-down resistor (4.7k is typical) that overpowers the internal pull-up. See the Open-Collector Signals App Note. Other options are the LJTick-Divider or RB12.
2. When your signal is in condition B, you need to protect the digital input from the high voltage. Per the Driven Signals App Note, you can do that with a series resistor, or the LJTick-Divider or RB12 are great options.
I would suggest that the LJTD-5 takes care of both issues for you.