2023-11-11, 10:59 AM
(This post was last modified: 2023-11-11, 03:54 PM by baltika_no_9.)
Yes and no. Of course the ADC converts an analogue voltage to a quantized representation. It's output is always an integer in the range 0 to 32767 (for the ADS1115 which is a 16 bit device), OpenPlotter reads this and converts it to a voltage which is presented to Signal K.
Just because you are connecting a device which can output 0.5V to 4.5V does not mean that a value of 0 corresponds to the 0.5V and 32767 corresponds to 4.5V that's absurd.The ADS1115 has no idea what the min and max values might be of anything you happen to want to connect to it, it is just reading a voltage and assigning it to the nearest quantized value within a range. It has no further knowledge. So if I connect something that swings say from 1V to 3V it can't automatically adjust so that 0V returns a level 0 and 3V returns a level of 32767. The gain you set on the device determines the range of voltage it can measure; a gain of 1 for instance means it can measure 0V to 4.096V. If it is supplied with an input of 4.096V then the digital level will read 32767, If the voltage increases to say 4.5V then the device has run out of range, I cannot assign a higher value than 32767.
In fixing the gain for the ADS1115 you are fixing the intervals between each voltage step it can resolve. What you have to do is to set the gain and/or use a potential divider to ensure that the voltage presented to the ADC is within the range for the gain specified and within the overall capabilities of the ADS1115 (e.g. no more than around Vcc +0.3V).
Just because you are connecting a device which can output 0.5V to 4.5V does not mean that a value of 0 corresponds to the 0.5V and 32767 corresponds to 4.5V that's absurd.The ADS1115 has no idea what the min and max values might be of anything you happen to want to connect to it, it is just reading a voltage and assigning it to the nearest quantized value within a range. It has no further knowledge. So if I connect something that swings say from 1V to 3V it can't automatically adjust so that 0V returns a level 0 and 3V returns a level of 32767. The gain you set on the device determines the range of voltage it can measure; a gain of 1 for instance means it can measure 0V to 4.096V. If it is supplied with an input of 4.096V then the digital level will read 32767, If the voltage increases to say 4.5V then the device has run out of range, I cannot assign a higher value than 32767.
In fixing the gain for the ADS1115 you are fixing the intervals between each voltage step it can resolve. What you have to do is to set the gain and/or use a potential divider to ensure that the voltage presented to the ADC is within the range for the gain specified and within the overall capabilities of the ADS1115 (e.g. no more than around Vcc +0.3V).