josheeg
Member
reading a serial digital sensor should there be a resistor on its output? the output seems to get random noise random 1s where zeros should be whale its printing the sensors input that should be fixed.ads1298 dout page 13
"Specifications apply from 0°C to +70°C. Load on DOUT = 20pF || 100kΩ."
josheeg
Member
It apears the print statment took too long and was getting overwritten or something because the samples were at 500 samples per second print out 24 characters and line feed carage return the data seemed to show 1's or 0's where it shouldn't be but then I lowered it to 250 samples per second and the printout seems consistant at least a screen worth.
"Specifications apply from 0°C to +70°C. Load on DOUT = 20pF || 100kΩ."
I believe this means that the specifications given were verified with 100kΩ of load resistance (which implies it's resistance to ground) and 20pF of capacitance (to ground because "||" means "in parallel with") on the output pin. The implications of this are that you should be able to reach the stated performance if your circuit has LESS capacitance and resistance loading the the circuit than this. The STM32 typically has 5pF load capacitance on each pin (p58 of datasheet) and you add some pF with your PCB traces. If they're crazy long or go through a cable or something, you might have something to worry about. The load resistance is going to be the input impedance of the pin, which I was unable to locate on first pass in the STM32 documentation just now, any series resistance. The likely answer to this is that the STM32 inputs have much higher input impedance than 100kΩ.
tl;dr?
No, you shouldn't add a resistor. You want to be as much below the values given for load capacitance as possible and as much above the values given for load resistance as possible.
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