Pull up resistor wiring
23 May 2017 07:23 #93520
by royKO1405
Pull up resistor wiring was created by royKO1405
I am new to cnc building and I have a question about the pull up resistor. In the manual the schematic shows how the resistor is to be installed but I what do not understand is does the resistor take power from the input and then returns it to a neutral point, or does the resistor take power from another source and uses the input as a neutral. I am using the infamous Chinese TB6560 Blue board.
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23 May 2017 12:26 #93526
by rodw
Replied by rodw on topic Pull up resistor wiring
Try this video. It helped me a lot even though the hardware is different.
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23 May 2017 12:31 #93527
by andypugh
Replied by andypugh on topic Pull up resistor wiring
Which manual is suggesting that you should install a pull-up resistor?
An input pin often[1] measures voltage relative to a common 0V reference, variously referred to as Gnd, Neutral, Vee...
The input can be pulled up to a voltage high relative to this reference voltage, or be pulled down to the reference voltage. Then whatever sensor or switch you are using needs to pull the input pin the other way with a resistance less than the pull-up / pull-down resistor. In effect you end up with a voltage divider, and the two resistances need to be sufficiently different to swing the input past the detection limits.
[1] And equally often the input is an opto-isolator that needs current from + to - to turn the input on. Depending on the board the actual external pin might be connected to LED- with an internal connection from V+ to the LED+, in which case you connect the input pin to GND to turn it on, or the other way round, in which case you connect the input to some voltage higher than the GND. In this case it is much simpler to think in terms of current-flow than voltage.
An input pin often[1] measures voltage relative to a common 0V reference, variously referred to as Gnd, Neutral, Vee...
The input can be pulled up to a voltage high relative to this reference voltage, or be pulled down to the reference voltage. Then whatever sensor or switch you are using needs to pull the input pin the other way with a resistance less than the pull-up / pull-down resistor. In effect you end up with a voltage divider, and the two resistances need to be sufficiently different to swing the input past the detection limits.
[1] And equally often the input is an opto-isolator that needs current from + to - to turn the input on. Depending on the board the actual external pin might be connected to LED- with an internal connection from V+ to the LED+, in which case you connect the input pin to GND to turn it on, or the other way round, in which case you connect the input to some voltage higher than the GND. In this case it is much simpler to think in terms of current-flow than voltage.
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23 May 2017 14:13 #93543
by royKO1405
Replied by royKO1405 on topic Pull up resistor wiring
Hi Andy
Linuxcnc Getting Started V2.5, 2012-04-01 section 5.9.3 Home and limit switch options. From your first reaction are you saying that I do not require a pull up resistor. I think I understand what you are saying I will build a test rig and try what you say. ( at 69 I am just starting to play with electronics).
Linuxcnc Getting Started V2.5, 2012-04-01 section 5.9.3 Home and limit switch options. From your first reaction are you saying that I do not require a pull up resistor. I think I understand what you are saying I will build a test rig and try what you say. ( at 69 I am just starting to play with electronics).
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23 May 2017 14:16 #93545
by royKO1405
Replied by royKO1405 on topic Pull up resistor wiring
Hi rodw thanks for the link, I had actually seen that in my trawling through the internet and it does give an idea on what to do.
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23 May 2017 14:33 #93547
by andypugh
You only really need the pull-up on a bare parallel port. The TB6560 board that you have will (probably) have something built-in.
Replied by andypugh on topic Pull up resistor wiring
Linuxcnc Getting Started V2.5, 2012-04-01 section 5.9.3 Home and limit switch options. From your first reaction are you saying that I do not require a pull up resistor.
You only really need the pull-up on a bare parallel port. The TB6560 board that you have will (probably) have something built-in.
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