Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Infrared TX problem (Urgent, need help!!)

Not open for further replies.


Newbie level 3
Sep 1, 2009
Reaction score
Trophy points
Activity points
fpga sirc project

It is a small project at work that I design a generic IR TX controller. Carrier frequency, bit-time, and the number of carriers per bit time are all configurable. The controller has been loaded into FPGA, with the TX signal connected to a FPGA output, which is then connected to a mono 3.5mm phone jack. I bought a LED emitter, which can be plugged into the phone jack on one end, and the other end is the TX LED.

I configured my TX controller to send out a sequence that executes the Sony SIRC protocol, but when I pointed the TX LED against the Sony DVD player, the DVD player doesn't respond to it.

The sequence that the TX controller sends out is exactly the same as that shown in

FPGA drives 3.3V for logical '1', 0V for logical '0'.

I have checked the sequence that I sent to the phone jack and it is all correct. I am stuck right now, and any idea/help is appreciated.


Are you sure the LED is wired correctly? (Cathode to ground, anode to FPGA.)

If you move the DVD player really close to the circuit, does it work?

The FPGA may not be able to drive the IR LED hard enough to communicate. Typically, at least a driver transistor is used between the FPGA or microcontroller and the LED.

There is a trick you can use to estimate the magnitude of the IR output. Many digital cameras and camcorders are sensitive to IR light. Look through the viewfinder and press a button on the handheld remote. Do you see a flash? If so, then do the same with your circuit. No flashes or weak flashes mean you have problems with the IR LED driver stage.

I used the digital camera trick, and found that the LED wasn't emitting any signal.

Our FPGA board designer thinks that the board shorts the left channel and right channel by mistake. Since my plug is a mono plug, it could mean that the right channel is shorted to ground, and thus the left channel is also shorted.

I need to mod the board, and see if it helps.

Not open for further replies.

Part and Inventory Search

Welcome to