UIRT2B External Connections

This page describes how to assemble the external connections for the PCB power, IR emitters, IR receiver, serial port, and external trigger.

Connecting Power to the UIRT2

The UIRT2 requires +5V DC to operate and if using the PC power-up feature, standby (always on)  power must be supplied to the PCB.  ATX based motherboards have a +5V standby supply on the Wake On Lan (WOL) connection and is the recommended power source. The WOL connector needs a straight 3 wire pin to pin connection. 




If the WOL connection is already used or not available, you must find an alternative +5V supply and ground  as shown below. You will not be connecting to any WOL signal, just the two wires to get power to the UIRT2. Other possible sources of standby +5V are: power button, Wake On Modem (WOM) / Wake On Ring (WOR), keyboard, mouse etc... Motherboards are not standardized on these features except for WOL that uses a positive pulse to wake-up. WOM uses a negative pulse. The power button usually uses a negative pulse but should be verified.


For WOM or the power button you have to use Output 4 to generate the negative pulse.


Alternative +5V sources 

Connectors on a typical power supply may be used for +5V and GND but are not a standby (always on) source.

+12V = Yellow, +5V = Red,  GND = Black


Connecting the UIRT2 Serial Port

If a DB9 connector is mounted on the PCB , a short 9 pin male - female cable is needed to connect the PC serial port and the UIRT2. The cables are easily sourced and is included in the kits and with assembled units.

An alterative method is to solder the connecting wires directly to the UIRT2 DB9 solder pads. If ICSP is not required only GND, RXD and TXD need connection.

Connecting the IR Receiver

Connect the receiver module to the plug as shown below. Make sure the plug housing is slipped over the cable before soldering the wires to the plug . Use a  general purpose housing for the IR receiver and shielded multi-conductor cable to reduces noise interference and increase transmission reliability.  

Verify the pin out of your receiver and connect accordingly.
Tip = +5V
Ring = Data
Barrel = GND


Vishay TSOP4838


Note the image above is shown with the round receiver lens facing upward.

Important Notice: There have been reports of excessive noise on the receiver line. The PC appears to generate noise which causes UIRT2 and Girder to have poor stability and reliability.  The following steps clean up the signal significantly and are highly recommended.

1) Use quality multi-strand shielded cable to connect the plug to the receiver.

2) Add a ferrite core and a .1uF capacitor to the receiver circuit to reduces further reduce interference.

Connect a ferrite core in series on the + pin of the receiver and the incoming + wire. Connect the .1uF capacitor between the + pin and the GND pin of the receiver. Ferrite cores may be found on many discarded PCB, particularly on modem cards. 


Connecting the IR Emitters

Connect 2 leds as shown below. Make sure the plug housing is slipped over the cable before soldering the wires to the plug. Use a  general purpose housing for the IR emitters and a quality multi-strand shielded cable to reduces noise interference and increase reliability.

You can also use pre-wired emitters (like Xantech) but the value for R5 and/or R6 will have to be defined depending on the type used and rewiring the plug might also be necessary.

Tip = anode (+)
Ring = cathode (-)
Barrel = GND

.NOTE - The LED's round side has the longer wire is anode (+)  and the flat side with the shorter wire is cathode (-).


Connecting IR Emitters and Receiver Directly to The UIRT2

If jacks are installed this information does not apply. However if you do not use jacks, hardwire the emitter cable directly to the UIRT2 PCB using the following diagram.

Connecting Visible LEDs or Relays

There are three darlington outputs available to connect visible LEDs or relays. These outputs are independent of the IR emitter outputs and are controlled by Girder (UIRT plugin) or a dedicated IR code  (PIC programmable). They are set and operate identically to the WOL/Power switch output since it uses the 4th darlington output.

Power for these devices must be well chosen. +5V standby power can be used if there is sufficient supply. If relatively high loads will be connected, a better supply is the standard +5V or +12V which can be derived from a spare hard disk or floppy connector (red is +5V, black is ground and yellow is +12V). The outputs can handle currents up to 500mA but for most applications it is recommended not to exceed 100mA. A simple application is a visible led for indication purposes. R10, R11, R13 provide a resistor in series for the external emitters. Resistor value depends on the desired brightness: 180 (high) to 330 ohm (low)  for +5V, 560 ohm to 1K for +12V external power.

A clamping diode is required when switching inductive loads. At turn off, the EMF creates a high voltage peak that may destroy the ULN chip. Use a 1N4003 that is easily obtained.  The relay should have a coil resistance of 120 ohms or higher so the current through the ULN does not exceed 100mA on 12VDC.

Configuring these outputs is done in the PIC configuration of the UIRT Girder plugin, same as the WOL settings . The outputs can be set to pulse, toggle, set on, and set off.



A clamping diode is required when a relay is connected.


Connecting the External Trigger

This contact, when closed, signals the PIC to send a preprogrammed IR command to Girder that perform an assigned action