Motor/Light Block

My Lego Mindstorms Compatible Motor/Light Block



Just for the sake of having it, neither I nor this site have any affiliation with Lego, Lego group, Lego systems or Lego MindStorms. Also, I am not responsible for any damage to your RCX and/or computer that may result from the use of the knowledge/designs stored on this WebSite.

My Lego Motor/Light block

This is invention/design # 3 of my ongoing attempt to improve the abilities of the Lego Mindstorm system.

This motor/light block was designed November 17th 1998. Built March 30th 1999.

Like most of you, I quickly discovered that three output pads were not enough. This project explains and details how to construct my motor/light block. This project is not difficult to construct and I feel that anyone with patients should do fine.

Difficulty rating: Easy to Moderate


This motor/light block operates by connecting one of the motor outputs from the RCX to the bottom of the motor/light block. Then to the top of the motor/light block (labeled 1 & 2) you plug in the desired motor/light leads. Now with the RCX you simply program your chosen motor pad Forwards to trigger one pad and Reverse the output to trigger the other pad. This is great if you are, for example, running a compressor pump & turning on some backup lights. The only downside is that you cannot run both devices at the same time. You can quickly toggle the output between forward and reverse as a stop gap Measure to get both units working. In some situations this will work. The other downside is that you lose approximately 20 percent of the power from the RCX (.6 volts to be exact). This is due to the diodes that I used. (If anyone finds a diode that does not lose signal please let me know)

How to construct it

First, like my last two projects (the Temperature Sensor & the Sensor Pad), this project uses the Lego Electric Plating (part #5037) for the connectors.

Select two 2x4 pieces of Electric Plating that you wish to use for this project. Take one of the pieces and carefully cut the underside metal as seen in the photo. (This can be quite difficult to achieve. Consult the sensor pad project for a more detailed photo) The red boxed area in the photo shows the two areas that you must cut. You MUST ensure that no current can get from the left to the right side of each of the two metal contacts. The two green dots you see in the photo show where the wires coming from the bottom plate will be soldered. (More on this below)

The next step involves soldering the two diodes in place. They will be jumpering the cut traces you have just done. Another thing to note is that you must insure that the diodes are Not both facing in the same direction. It doesn't matter which way each of them face just so long as they aren't both facing the same way. Once this is completed you must insure that you have not made a short. This can be easily checked with a multimeter. Set the multimeter on continuous mode (or buzzer mode) and putting each of the meter's leads to the ends of the trace you just soldered into the plate. You should get signal one-way only. If you get signal's both ways or no signal at all, then you have made a mistake.

Referring back to picture with the green dots you must now take two small wires and solder them to where you see the green dots in the example photo. For now keep the wires two inches long each. Test to assure you have not made a cold solder joint because if it comes undone inside once you've added the glue (as happened of me in a similar project) you will have a lot of work on your hands trying to salvage the project.

The next step is to hollow out a 2x4 standard block and cut out the Middle four pegs and surrounding surface. Do Not cut the outer walls. (See photo. I chose white because the Electric Plating is white but you may choose any colour you wish) This is quite the involved process, the best way I have found is to use a soldering iron and melt the unnecessary parts away. If you have a Dremmell, drill or other such tools you can achieve the same result. In the end your block should look like the photo.

Once the above is done, you should test fit the three pieces of your project. The bottom plate needs to have both wires soldered onto it. One on the upper row and one on the lower row. The best place to do this is onto the two inner pegs of each line. Select one for the top and one for the bottom insuring that you are not soldering where the hollowed out block will fit. Measure your wires to be just long enough to work with but not so long that you can not push the three pieces together.

Once it is together, test each connector with a multimeter. You must insure that none of the wires have come off. Once that is done and it is working properly, open the blocks a bit and apply your glue. (I used a five-minute epoxy) keep tightly press together until the glue sets. (for five-minute epoxy it is five minutes)

Allow the block to fully dry (five-minute epoxy takes 24 hours to fully harden) and label if desired.

Congratulations! You just completed the motor/light block.

That's about it, if you have any questions you may contact me via email. Enjoy!

Copyright 1999 by TFM-Designs - All rights reserved

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