You can use any digital port for the S1 and Gnd. I believe the Sabertooth Movement Panel expects you to use D0 (not home so can't look right not). You would connect to the ground and signal of the digital port.

You don't need the +5. The VCC port on the Sabertooth doesn't give a lot of amps, so if you are controlling anything other than the Sabertooth, you will want separate power to the EZ-B. If you are just controlling the Sabertooth, then the EZ-B will run on 5v, but you need to disable the low battery alert (and I woudl recommend an IoTiny, since you don't need all of the ports of a full EZ-B).

Depending on the voltage of your lawnmower, and what you are controlling, you could use the same power source as your motors or use the same power source with a good voltage regulator.

Alan

From the Sabertooth manual:

The 0V and 5V connections are 
used to power and interface to low-
power control circuits. 
The 5V connection is a 5V power 
output. The 2x25 utilizes a 1 Amp 
switching BEC to power the 
onboard electronics as well as to 
provide power to your receiver and 
up to 4 standard analog servos. You 
can power anything that requires 5V 
straight from the Sabertooth 2x25. 
There is no need for an external BEC unless you need more than 1 Amp. The BEC will work at 
full rated output throughout the Sabertooth’s operating voltage range. You can use the BEC at 
full capacity whether you are running 7V or 24V in.
The 0V connection is the signal ground for the Sabertooth. In order to receive input signals 
correctly, it must be connected to the ground of the device sending the signals. 
Using the 0V and 5V connections to power a radio receiver in R/C mode and potentiometer in 
analog mode is shown in Figures 2.1 and 2.2. If you are using multiple Sabertooths running from 
the same radio receiver, only one should have the 5V line connected.

Thanks Alan, much appreciated. I will use the ez camera. Will look up the power requirements for that

DM