RCX FTDI IR adapter “tower”

Despite the lack of resources that the RCX has compared to the NXT, I enjoy using it. It is a simple, small, and easy to use/build with controller.

The issue I have had with using it, is that there are no USB IR Tower drivers for a 64-bit OS, and I am running windows 7 64-bit on my main computer. Until now, I have been using a second computer for programming the RCXs (running Windows 98). I have an RS-232 IR Tower that works, but my computer doesn’t have a UART port. I could have used a USB -> RS-232 adapter -> IR Tower, but I didn’t have an adapter, and I like doing things the homebrew way, if you know what I mean. Therefore, I made an interface for my SFE 3.3v FTDI board to IR. Here are some pictures:

FTDI IR interface "tower"

FTDI IR interface "tower"

FTDI IR interface "tower"

The results seem pretty good, considering that no lego IR tower is involved. The only issue I have found so far, is the inability to download firmware. However, even fairly large NQC programs download without error. I think the FW download issue might be a lack of supply current (I am powering it all from the FTDI). The range is fairly decent; about 1 meter.

The concept is extremely simple, but there are several requirement made by it being IR. You must modulate the Tx at 38kHz (carrier frequency). I did this with a 555 (actually half of a 556) in astable mode. Another requirement, is that you disable Rx whenever transmitting, or the input buffer will fill up with all the sent bytes (the IR will go from the LED to the TSOP). To take car of this, I used a 555 (the other side of the 556) in resettable monostable mode. To reset it, I used a 2n3905 PNP transistor to drain the capacitor. Another thing I had to note, is the logic state of the lines. I used inverters for that. I also needed an OR gate, so I used a 4001 (NOR) for the OR and for the NOTs (inverters). I was able to get by with only two IC’s; a 556 and a 4001, plus the FTDI.

Here is the schematic (click on it):

Note, that it is my first schematic made with a schematic program, so it likely has errors.

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This entry was posted in Electronics, Mindstorms, RCX and tagged , , . Bookmark the permalink.

One Response to RCX FTDI IR adapter “tower”

  1. SavedCoder says:

    This is awesome, and it was useful when I was trying to figure out a remote control system.

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