|BEAM Projects > LM3909Vore|
From the CostaRican BEAM Site
Circuit used: LM3909 Circuit from the CostaRican BEAM site; I am not sure who originally developed this circuit, as the link on the CostaRican BEAM site is now dead. Thanks to J.W. Goerlich for letting me know that the originator is Jesse Meers. His site no longer exists but thanks goes to Jesse Meers for the circuit. J.W. Goerlich also pointed out that Harold Ilano used this chip in his RoVore. It does use the LM3909 but it also does alot more. Be sure to check out his site: Harold's BEAM Bugs
Behavior of Circuit: Each photodiode controls one of the LM3909s. With battery power, they oscillate and will drive the vore toward the light. Switch activation stops the motor on the side activated.
Construction Notes: Parts include: LM3909 (x2), motors (x2), Photodiodes (x2), 470uf Capacitor (x2), 2200uf Capacitor, feelers (x2), and a solar cell. To this list add a 20 pin dip socket to mount the two LM3909 ICs in and the two 470uf Capacitors. The LM3909s were originally sold as LED flasher/Oscillators (see datasheet). Unfortunately, they are now considered and obsolete part which makes them a bit hard to find. I located mine on eBay about a year ago.
November 10, 2008: I ran power and ground to the two LM3909's first. I also added a drop of hot melt glue to the top of the dip to hold the 470uf capacitors in place. The last picture in the first row shows the photodiodes attached (black squares with yellow and green heat shrink). I used solid core hookup wire for one lead on the Photodiodes. This will allow me to move the around and reposition them to an optimal place. The same picture show the white wires that will go to the sensors.Not exactly sure how I am going to do the feelers yet. I may just use two momentary switches that are normally open or I may make another set like the ones I made for the Modified Edgebot.
November 17, 2008: While the paint dried, I mocked up the motor mounts on some thin sheet styrene from my local hobby store. It was too thin to really support the motors well. But I really like the concept. The proto material I used was about .5mm. I have two thicker options, 1mm and 2mm. I am going to give the 1mm a try. The 2mm will be too thick to use the attaching screws.
After the paint dried, I removed the non-essental plastic bits from inside the mouse to make room for the motors and electronics. I am also going to add a battery option to the circuit using 2-3v CR2032s wired in parallel. I used a single CR2032 for testing and it worked well undAfter the paint dried, I removed the non-essental plastic bits from inside the mouse to make room for the motors and electronics. I am also going to add a battery option to the circuit using 2-3v CR2032s wired in parallel. I used a single CR2032 for testing and it worked well under no load conditions. I may just for go the solar cell all togehter...
November 21, 2008: I found a set of tires to mount on the motors. I will need to drill out the centers a bit to make them fit. They are a set of light weight foam tires for a rubber powered airplane. The switch will exit the cord hole (which would, on a normal mouse, be the front); however, I am going to drag the front.As you can see from the mock up, it should look fairly nice once all of the wires get tucked away. Testing showed that the bump switches just kill the motor on the side that is grounded. I am not feeling very confident in this bot's ability to get out of trouble. I am also going to only use a solar cell and capacitor to run this bot. I am going to use a 4V Open circuit solar cell and a 2200uf capacitor. Once I get the sensors and wheels installed, I may modify it some.
November 24, 2008: Well, I didn't get the ‘bot done this weekend. I ran into several issues. First the solar cell just doesn't give it enough amperage to move the weight. A 9V battery dropped to 5V did the trick. I added a 78L05 (see data sheet for pinout) to the switch to deliver the 5V. The next issue was where to put the battery. I ended up skeletonizing the mouse cover to make room for it to fit. Another thing that may be an issue is how low it rides to the ground. I will probably need to adjust the motor angle to gain a little more clearance. I still have to make the sensors but I will be confident that it will move.
November 25, 2008: I made the sensors almost like the ones that I made for the Modified Edgebot. The parts are almost he same as well (2 pieces of 1/8in x1/8in tube, and 6in of brass wire). The difference is that I wrapped the tube piece with two bits of wire. The only reason that I did this is for attaching the sensor leads to it. When I was making them this time, I tended to desolder the tubes! How annoying...The battery is removed through the top hatch. If there is no load on the motors, they just spin away. But, with weight on the wheels, it waggles toward the light. I was correct in assuming that it wouldn't have much success getting away from obsticles. However, it performs well otherwise. Check out the BEAM Gallery for bigger pictures...