59
Digital I/O
Output Examples
Controlling an LED
Let’s say you want to light an LED while a cable is attached to the tester. In the User Preference
Set Digital Output
, you can choose to configure one of the outputs. In this case, choose output
pin 10. For this output pin, select
Cable Attached
to set, and
Cable Removed
to reset the
output.
In this example, the LED requires only 20 mA; therefore, we can use the +5 VDC supply on the
digital /IO port to power our circuit. Use a resistor in series with the LED to limit the current going
through it.
Pin 9
DC +5 Volts
Pin 10
Output
Resistor
LED
How do you choose the resistor? The LED in this instance has a forward bias voltage drop of
two volts; therefore, three volts must drop across the current limiting resistor. Knowing voltage
drop and current through the circuit, Ohms Law can be used to determine the resistor value.
R =
V
I
=
3 Volts
0.020 Amps
= 150 Ohms
When the cable is attached, the tester will pull the output to ground allowing current to flow in the
circuit, and the LED will turn on. When the cable is removed, current though the output will stop,
and the LED will turn off.
Turning on a Light
Let’s say that instead of an LED you want to turn on a light bulb powered from a 120 VAC wall
outlet. A relay can be used to control the light bulb. In this example, we select a relay that has a
coil voltage of 12 volts and draws less than 100 milliamps so we can use the +12 VDC power
supply on the tester. The relay circuit is as shown.
Pin 6 Output
Diode
Relay
Pin 12 +12 VDC
A diode, such as a 1N4002, is added across the relay to protect the digital I/O port from the
reverse current created from the coil when the output turns off.
Summary of Contents for 1100R+
Page 1: ...Version 2011 1 0 November 10 2011 1100R User s Manual...
Page 28: ...24 Using the Tester...
Page 78: ...Connections continued Net Test Points Components...
Page 79: ...Notes...
