OK 2am now and I think I have done it.Board now has 2x ADS1115 16bit ADC's now Inputs come via 2x 4 channel op amps with a divide by 2 setup. In theory, from what I know at this point in time, it should be possible to put in +/-10V, +/-5V, 0-10V and 0-5V now.Will do more reading tomorrow.CheersJames
I think I have clicked.So the -ve scale output is purely for if the -ve input is higher than the +ve input, so 5V vs GND, rather than GND vs 5V.And differential is so you can do 1V to 4V for instance, and still get full scale...I think you got it. The ADS1115 is a 16 bit ADC only if run in the differential mode and has a 2s complement integer output conversion (same format as a arduino integer), so full range voltage to + input and ground to - input, converts to a 32,767 value, and ground to + input and full range voltage to + input returns a-32,768 value. Equal voltages applied to both + & - input pins returns a 0 value conversion. When run in single ended input mode it becomes a 15 bit ADC with 32,767 returned with full range voltage on the + input and 0 if at ground voltage. The true value of having and using the differential input mode is when wiring directly to a Wheatstone bridge type sensor (common for strain gauges and even thermistors) where the bridge's north connection is wired to +5vdc, it's south terminal to ground and the output taken from the east and west terminals directly to the diff input pins. At balance both measurement points will be at 2.5vdc and the ADC will return a value of zero counts and no matter which direction the bridge becomes unbalanced as the sensor(s) in the legs change resistance, will return either a positive or negative integer conversion value. That coupled with a full gain range allowing +/- .256 volts DC and one can see that it's a very sensitive measurement, as step resolution will be on the order of 8 uv if I did my math right ! That kind of resolution performance normally requires quite expensive instrumentation op-amps and very careful wiring layout. Ok so this isnt capable of +/- inputs still, so I can remove some of the complexity i added by changing opamps, adding a -ve supply for the op amp, etc etc.Correct, no negative voltages relative to ground, or voltage above the Vcc allowed on any pin of the device.I have used the MAX127 before which takes 0-5, +/-5, 0-10, +/-10 etc and is software selectable etc, however not cheap at all.Obviously what that does is not so simple to reproduce.Nice chip, somewhat large package size(lots of input channel pins ). Only real feature missing is programmable internal op-amp gain stages for measuring low level signals without requiring external amplification. Also lack of differential input mode then lacks the automatic common mode noise rejection that differential input gains you. However that's not something that can't be added with an external instrumentation differential input op-amp with programmable gain settings(?). There seems to be just thousands of ADC chips out in the wild these days, so getting the features one needs and nothing extra, is just a matter of the time consuming task of checking all those datasheets. I was just very impressed with how many features and high performance they packed inside such a tiny package for the ADS1115. The internal voltage comparator mode with a independent output pin would make a great interrupt generating voltage monitor function, think low battery monitor/alarm, with very little software overhead in the controller chip, just a short ISR routine to save variables to EEPROM and shutdown safely.Lefty
@RetroleftyDid you get a usable 16 bits from the chip? Any issues like special PCB layout etc?______Rob
That is an awesome looking voltage source!
Please enter a valid email to subscribe
We need to confirm your email address.
To complete the subscription, please click the link in the
email we just sent you.
Thank you for subscribing!
via Egeo 16