DanAndDusty 62 Posted April 19, 2011 Share Posted April 19, 2011 Hi all, Im a software guy starting to get to grips with the MSP430 (and the electronics world as a whole). I grok the digital domain fairly well but at the moment its the analog side Im getting to know. Im about to try and get to know the ADC side of the MSP430 and as a test I want to put a pot onto it and display the readings on a nokia 3310 LCD display. I have the display working well and I know how I plan to attack the ADC side, but my question is regarding the safest way of connecting the pot to the MSP. My understanding is connect the outer pins of the POT to VCC and GND with the center pin (slider) to the ADC pin on the MSP. I have a 22K Linear rotary pot lined up. From what I can work out the pot acts as a voltage divider and that all makes sense. My query is how to handle the case when the pot is fully rotated. When the GND side is almost 0 ohms the VCC side will be about 22k and all will be well.. however in the converse situation the VCC side is about 0 ohms all the juice has a free smooth path to the ADC pin and there will be nothing to restrict the current. My options (as I see them) are: 1) A 10k resister between VCC and the top pin of the pot. The top side will then range between 10k and 32k ohms, with the bottom side going between 0 and 22k. My guess is that the full range of voltages will not be presented to the ADC pin. 2) A 10k resistor between the centre pin (slider) and the ADC pin. Top and bottom with both then range between 0 and 22k but the current path will always have atleast the 10k resistor to limit the current. I don't know if 10k+22K would restrict the current too much though. 3) Do nothing. The MSP will limit the current or not be damaged by it. I have googled this question and most sites I have seen seem to have have no limiting resisters but don't say whether this issue was considered. So I hope this question is clear enough and you guys/gals can further my quest for knowledge. If I was just going for it I think I would go for option 2 as my gut feeling is it supplies enough protection without restricting the ranges. Many thanks in advance Dan Quote Link to post Share on other sites
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