Friday, February 17, 2006

NXT to RCX Communications (and Back)

The guys over at HiTechnic are certainly keeping busy these days. Today, Steve Barker from HiTechnic told Jim and me that they are working on a new product which they call the HiTechnic Bridge.

The purpose of this new product is to enable communications between the legacy Mindstorms RCX and the new Mindstorms NXT.

Lego Mindstorms NXT versus RCX
The new Lego Mindstorms NXT next to the legacy Lego Mindstorms RCX.
Pictures of the HiTechnic Bridge will be available at
the official announcement of the product next week.

The new Mindstorms NXT has wireless Bluetooth capabilities to talk to many other devices. The legacy Mindstorms RCX communicates only using its infrared port, and Lego has decided not to include the infrared port on the NXT. On the forums and blogs, proposals have been made to solve this problem. Since both the RCX and the NXT can talk to the PC, the idea in most of these proposals is to have the PC relay the messages between the NXT and the RCX.

Lego IR towers
Two versions of the legacy Mindstorms RCX IR Tower that connect to the PC.

The PC-as-middleman is a great solution when the RCX and NXT are not on the same robot. However, if you want to combine the RCX and NXT on the same robot, things get a little messy. Because Bluetooth is based on radio waves, the NXT brick does not need to keep in line-of-sight with the PC it is communicating with. This provides it with great mobility options. However, the RCX needs to point its infrared transmitter/receiver at the IR tower which usually is right next to the PC. By combining the RCX and NXT on the same robot, you must again point the RCX (and the entire robot) to the PC. This is undoing the benefit of the Bluetooth connection, and as a result, it is quite likely that you will prefer not to use the RCX Brick anymore.

The new product that HiTechnic will announce in a couple of days provides a simple and elegant solution to this problem: the HiTechnic Bridge contains an infrared (IR) transmitter and receiver, and is controlled using a NXT Brick sensor port. Instead of connecting the IR Tower to the PC, the Bridge is essentially an onboard “IR Tower” that you can connect directly to the NXT Brick.

The PC can communicate wireless via Bluetooth to the NXT brick, and the NXT brick can send commands to the RCX using the Bridge, without keeping line of sight to the PC. The HiTechnic Bridge turns the legacy RCX brick in a perfect slave computer, without sacrificing the new freedom that comes with the NXT brick.

Keep in mind that to program the RCX, you will still have to use the old RCX software. There is no software compatibility between the RCX and the NXT brick, and the HiTechnic Bridge cannot resolve that. However, it is possible to stop programming in the old RCX environment, and still use the RCX as a slave computer. Simply run software on the RCX that takes commands from the IR port, and drives the motors with them, and returns all sensor values to the IR port. That single program should be able to serve all your future needs. You can stop programming the RCX and let the NXT do the thinking.

The HiTechnic Bridge has full bi-directional data transfer. Either the NXT or the RCX can initiate the communication, depending on how you program your robot. The HiTechnic Bridge should be available by the time Lego Mindstorms NXT launches in the fall of this year.


At February 17, 2006 10:03 PM , Blogger Jim Kelly said...


Again, good commentary. I hope visitors to both our blogs are finding things to keep them interested in NXT!

HiTechnic certainly deserves a lot of credit for not only developing, but SHARING, this information. It's nice to know that even before the retail release of NXT, that people are developing add-ons for the product. I have a feeling that this version of Mindstorms is going to explode with options - more than RCX - due to the flexibility of this new design.

Maybe we need to combine our blogs?! Make it easier for people to find NXT info in one place! :)

I told Steve at HiTechnic - if there's NXT news out there, one of us is going to find it!


At February 18, 2006 2:13 AM , Anonymous Filip said...


The interesting thing about the Lego Mindstorms NXT environment is that is going to be filled with smaller companies adding value to the set. I think that is a brilliant move on the part of Lego, and one I hope will pay off for them.

HiTechnic is setting a great example. I like the way they extend the capabilities of the NXT brick, but stay with NXT's elegance and simplicity. Frankly, I'm a software guy, and I love the way I can just plug-and-play the mechanics, sensors and motors parts. Off course, we haven't seen the prices, but at least technically they are doing things "the right way".

On combining the blogs, that could certainly be a good thing, but let's discuss on the pro's and con's by email. Right now, there is also the MDP and NDA to consider. So far, no news on that front here.


At June 07, 2006 2:57 AM , Anonymous Drew Stevenson said...

Any word on whether the bridge (or a software patch) would allow Vision Command to be a remote sensor via NXT BT or IRbridge systems?
Do all these new add-ons work with the NXT base software (or do you need to do text programing). Do they just pretend to be other sensors with similar output (ie 360 rotation = compass, 256 light value = 256 IR comands etc)
Could you illuminate this a bit or even have an article about it?

At September 20, 2006 7:01 PM , Anonymous Eric D. Burdo said...

Mindsensors has a similar device already shipping. I haven't tried it yet to see how well it works, but here is a link:

At September 25, 2006 5:00 AM , Blogger Drew Stevenson said...

I think that HiTechnic should while they are at it build in a Legacy IR bridge feature for Spybotics, IR remote car and the Mantas etc. There are about a 1/2 doz. Lego products that use IR remotes to control electric bricks (and almost all the remotes are interchangable - and thus it'd be simple to add much more range with just one additon).

At December 08, 2006 3:52 AM , Anonymous Anonymous said...

I have discovered a simple way to communicate between the NXT and RCX. NQC has a command called Sendmessage() which turns on an IR light on the RCX. The light detector on the NXT will respond to this signal which you can write code for. You can also use the Basic Stamp (Board of Education) to communicate with the NXT using an IR LED. I tried this and both methods work fine. These options will provide added capabilities that may prove helpful.

M. Flake

At December 29, 2006 5:44 PM , Blogger K said...

Sounds great, if not too pricey (under US$25 would be nice).

So ... Bluetooth would not be necessary to use it, right (please!)?



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