Adding external sensor inputs to the Nora. Would this work? (is it a good way to do it?)

Hello fellow impthusiasts

I want to upgrade the nora so that I can connect external wired analog sensors to it. I will be using1/8" stereo phone jack connectors.
The analog sensors I am currently using has 3 pins: VCC, GND and signal. Output signal is 0-3V. Supply voltage 3.3-20V

I have attached my schematic. The block ‘Analog sensor input circuit’ is the one I added. I haven’t altered anything else in the original schematic.

Should i use the ‘VBAT/3V0’ directly from the boost converter or the ‘3V0_sensor’ from the powergate to supply my analog sensors?

Hi Toebs,
I love the idea of hooking up those sensors up.

Here’s a couple suggestions:

  1. You should adjust the power supply feedback network (R15/16) to get 3V3 out which is required by the VH400.
  2. You should use 3V0_SENSOR for both the sensors themselves (as you have already done) and the input op-amps (U80).
  3. Not all the pins on the imp have ADCs, you have several analog signals connected to non-analog capable pins. You will need to re-arrange which pins are connected to what, but things like SENSOR_EN_L don’t need to be on ADC-capable pins which they currently are.
  4. I do not think your op-amp circuit will do what you want it to do, you should go back and check. Likewise, your protection needs to be on the input signal itself.
  5. U4 appears to be un-powered.

Hope you find this feedback helpful. Good luck!

Hello Brandon

Thanks for the informative and very helpfull reply!
I attached a new schematic.

  1. Regarding to the boost converter data-sheet, the current configuration of R15 = 270k and R16 = 43k should give 3,3V. From the datasheet: VOUT1 = 0.45 × (270k+43k ) / 43k = 3.276V. Or have i missed something?

  2. thanks will do that, can you explain why so i might learn?

  3. Thanks i have fixed it. Moved the SENSOR_EN_L as suggested and reduced so I only have 3 inputs, utilizing card pin2, 10 and 11. I am not sure how the ‘sensor_drain’ on card pin 5 works, so i am not sure if it needs ADC, and hence i did not re-asign it.

  4. Duh what a blunder on my part. The sensor signal should have been connected to ‘+’ on the op-amp and not to ‘-’. I think it is configured corretly now, or am i still mistaken?

  5. thank you!

I was to hasty in uploading the last PDF schematic (i forgot to configure the unused op-amp).
I have attached a new pdf here.