mb944 Posted June 7, 2004 Report Share Posted June 7, 2004 hi!my friend has got a bag full of nice long 2k pots and 20k pots, but no 10kwould either of these work ok?thanks-al Quote Link to comment Share on other sites More sharing options...
pay_c Posted June 7, 2004 Report Share Posted June 7, 2004 Yeah, both *should* work fine.With the 20ks there could come in some more noise. You can avoid that by a good shielding (alu frontplate & housing - no plastic).The 2ks need a little more current (5 Volts @ 2kOhm about 2,5 mA per pot, making 160 mA for 64 pots - that´s a little much!) but nearly don´t bring in any noise anytime! If you use those, just make sure your current stays below the max rating for your PSU and the 7805 (that´s 1 Amp with a good heat sink).Greetz! Quote Link to comment Share on other sites More sharing options...
Guest wavemachine Posted June 13, 2004 Report Share Posted June 13, 2004 alternative you can put a 20k resistor parallel to the 20k-pot and it´ll work as a usual 10k-pot !! But that doesn´t work with the 2k-pots !Have fun... Quote Link to comment Share on other sites More sharing options...
acidcode Posted June 14, 2004 Report Share Posted June 14, 2004 I think when you put 20k in parallel it wont work linear... Quote Link to comment Share on other sites More sharing options...
Synapsys Posted June 15, 2004 Report Share Posted June 15, 2004 The data sheet for the 18F452 recommends that the source impedance for an analog input should not exceed 2.5K. The higher the source impedance the longer it takes for the ADC to acquire a change in the input voltage. In addition, as the input impedance increases so does the offset voltage at the input pin. This offset voltage is actually an error voltage. In this application I do not believe this error voltage is very significant. I assume that TK optimized the code to allow enough time to acquire a change in input voltage based on the 10K pot. That being said I would think the 2K pots would be a better choice since the acquisition time would be shorter than with a 10K pot. The 2K pot will as mentioned draw more current (2.5ma per pot) and pay_c is right about making sure the power supply can handle this load in addition to the load of the remaining circuitry. :) Quote Link to comment Share on other sites More sharing options...
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