Is a pull-up resistor necessary when using the breakout board?

Martin Cowley

Hi everyone,

I've had my Twine setup for some time now, and have had it in a couple of roles so far (both involving the breakout board); monitoring a current sensor or float switch on my sump pump, and as an Internet-enabled doorbell.  In both cases the switch is normally open, and is closed upon activation (sump pump runs and draws power, sump bucket water level triggers float switch, someone presses the doorbell).  I've been using a pull-up resistor between the power and input lines on the breakout board, as per one of the first Twine blog posts (pre-shipping I think, so a while ago) about setting up a photoresistor.  I'm wondering if the pull-up is necessary however, given the Twine breakout seems to have a 4.7K resistor built in, and none of the recent blog posts (e.g. about setting up an Easy button) mention the need for a pull-up resistor.  Was this some kind of design change on the Twine, and am I safe using my Twine without the pull-up?

Thanks!

Martin.

Christina

Sorry for the delay, I was waiting on an official response from the engineers.

There is a 4.7k resistor on the twine PCB that is used for a pull up of the external sensor.

We only turn the pull up on briefly when looking at the state of the external sensor. 

Using an external pull up will draw more power and shouldn't be necessary in most cases. We suggest that you try the application without the pull-up first and then move to using it only if necessary.