i decided to do a quick and dirty project to make a lego r/c car functional again. the car was already built so the project was mostly electronics. i spent 2 days updating the firmware to support an i2c motor driver board, to support saving of settings to the eeprom, and to add a makeshift telemetry protocol. needless to say my quick and dirty project was no less dirty but much less quick. i tested, squashed some bugs and it ran well.
my rc board needed some work. it consists of an atmega328, with a header for a nordic nRF24L01+ radio module, and headers for servos and i2c devices, all crammed onto a radioshack proto board. first of all it needed an on board power supply. none of my supply boards were small or put out the neccisary power. i needed a couple of amps @5v. a 7805 just wouldn't cut it (no matter how big of a heat sink i use). so i decided to build a switch mode supply with a lm2576 step down switching regulator. it only takes like 7 components (the lm2576, an inductor, schottky diode, 2 caps, and 2 resistors). needless to say i grossly overestimated the amount of available space on the board.
i had to bore out a couple of the holes because the leads on the diode were really fat. but i managed to cram everything in. needless to say the switch mode components ended up really close to the radio. as a result the radio didnt work, too much rf noise. after scratching my head for 3 hours, i grabbed a card slot cover that i left on my work bench, jammed it between the radio and the switch mode supply, and then i clipped it to ground. after that everything worked fine. after that i quit and went to bed. this morning i found a pcb from an old radio, and began desoldering the rf fences from the sensitive rf components, i cut and bent and hammered that piece of sheet metal into a makeshift rf shield, to surround the power supply and isolate it from the rest of the board. so now all that is left to do is put it back in the car and see what happens.
