Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

Pololu Forum

Using a Hall Effect sensor as a homing and limit switch for Tic

I want to use the Hall Effect sensor as a homing and limit switch. https://www.sparkfun.com/products/14709
This has three leads – power (VDD), GND, output. Bring a magnet close and the output acts like a switch. If I put a 10K pullup resister between output/VDD, and use a VOM to measure Voltage between output and GND, I get “0” V as the magnet gets close and 5V when the magnet is far away. I think this means that the 0V situation is “open” and the 5V situation is “closed” in the context of a switch. Can someone explain how to wire this to the Tic controller so that it acts as a limit switch?

Hello, Jim.

You can find a detailed explanation for limit and homing switches in the “Setting up limit switches and homing” section of the Tic user’s guide. Based on the behavior you described, you should be able to make the following connections and enable the internal pull-up resistor as explained in that same section of the user’s guide to get it working:

Sensor    Tic
GND   -   GND
VDD   -   5V(out)
output -   SCL, SDA, TX, RX, or RC configured as a limit switch


Hi Brandon,

Can you clarify, please? Can I use a Hall Effect Sensor and use the internal pull-up resistor on the Tic, thus there is no need for an additional external pull-up? I believe this is correct, but I want to confirm prior to connecting my sensor to the Tic. Also, is there a better output pin to use for this application? TX/RX or RC? I’m using I²C.

My plan was to wire in this manner:

Sensor    Tic T825
GND    -   GND
VDD    -   5V(out)
output  -   RX configured as a forward limit switch, pull-up 



Hi, Andy.

That is correct; you can use the Tic’s internal pull-up and do not need an external resistor. The RC pin is actually pulled down and meant for a different normally closed type switch, but either the TX or RX pin should be equally fine.


1 Like