Tuesday, April 27, 2010

Common Ground -> Progress -> *Baseline* -> Refine -> Extension

We are using the DC motor that came with the car so it did not need to be mounted, however the servo motor still needed to be attached. I used Evan's dremmel again to shave off the arms of the servo and then mounted the servo onto the front of the car using electric tape. With the servo and DC motors working correctly, we pretty much had a RAC car. And on top of that, we also had a functional lighting system. However, with the HC12 tied down to the project board for power, we couldn't technically drive the car more than the length of our shortest wire. Thus, we had to move the HC12 and everything else onto the car base. The problem with the HC12 was that we weren't sure how to power it. Initially we fed its Vaux pin a 5V output from a voltage regulator, but this did nothing more than turn on the indicator LEDs on the HC12 (the DC and servo motors twitches so we thought there wasn't enough voltage/current going through). We also tried using the barrel connector, which seemed a more direct power input method. This returned the same result as using Vaux so we opened up the datasheet for the APS12 board. We learned that the microcontroller has a build in voltage regulator and accepts input voltages between 6V and, if I recall, 18V. We proceeded to give the +7.5V from the five AA batteries using both methods, but still got the same futile results. All this time we were trying different jumper combinations for each method. Furthermore, from the datasheet we learned that the board limits the current to 250mA, and using a power supply on the motors while limiting the current to 250mA barely moves them. After extensive debugging as shown from the picture, we decided to add another power source specifically to power the Hc12. This method worked and we were able to put together a working RAC car,  which is our baseline goal.

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