DATA LOGGER MANUAL
Manufacturers of low power instruments
page 117
Open Collector output
In electronics a common way of driving exter
nal loads is the use of an “open collector” output. This is a
transistor, with its collector left unconnected, for the benefit of user to connect to its load of interest. The
open collector (o.c.) is very versatile, and provides the possibility to use various voltages.
In the picture above, an open collector output is shown. The o.c. is only capable of sinking current and
NOT sourcing current. That’s why the “load” in the picture above is located in the “high side” . The
transistor will sink the bottom side of the
“load”, enabling current to flow through.
The user can choose his own voltage level, because the transistor only acts as a switch and NOT
supplying any voltage. In your YDOC data logger the maximum
“supply voltage” for the o.c. switch is
limited to 40 volts DC.
Using a relay to drive an external load
If you like a relay, in order to switch an external
“load”, please bear in mind that a relay can produce very
high these spikes to occur, always use a diode, connected in parallel with the
“load” .
Picture below shows how to do this.
The transistor and resistor shown, are part of the data logger PCB.
