Some more memories

While looking at my parents attic for some old stuff of mine I not only found my old electronics experimenters kit, but also my old Lego boxes. My son already got the more generic bricks I owned as a kit (together with all the sets he got for Christmas and his birthdays already). But I also owned a whole lot of Lego Technic sets, and bought myself a Mindstorms RIS shortly after they came out. And while digging around in the attic I found the latter one…

This is the original RCX version 1.5, still complete with the yellow brick and the infrared tower (connected via serial port). I also added the accessory kit later on.

Unfortunately, serial ports are increasingly difficult to find on modern PCs. When I upgraded the last time, I specifically looked for a mainboard with one, but today this severely limits the choice. So it seems like a replacement is in order.

RCX infrared communication

The infrared communication uses a 38 kHz carrier signal, and just sends normal bytes (bit-by-bit) via this carrier. Fortunately, on the PC side the infrared tower includes all electronics for generating the carrier and modulating the signal. So both ends of the communication (PC and RCX brick) just speak normal RS232 (though its with 5V levels on the RCX side).

Bluetooth upgrade?

So it should be (relatively) straightforward to replace the infrared tower with a Bluetooth module (just a small USB dongle), and use its serial profile instead of the port used normally. On the RCX side, the infrared circuit needs then to be removed, and must be replaced with another bluetooth module - one which just speaks UART.

Such modules are available cheap on Ebay. But since space is at premium, I might go to smaller modules like the ones from Panasonic. They are just 9 by 9 mm, so they might even fit into the RCX brick itself. They state to be for ‘HCI’ (human-computer-interface) applications, but the data sheets also mentions that they can be used with the SPP profile.