Interfacing circuit

[FreshmanNewbie]

I have an ADC and DAC whose reference voltage is 3.3V.

I am taking analog and digital inputs from this sensor and giving it to the adc and dac.
But the analog and digital outputs from the sensor is 5V tolerant. Whereas my ADC and DAC reference is 3.3V.

Can I use a simple voltage divider to reduce the voltage from 5V to 3.3V, or should I use a level translator IC?

 

[KlausST]

Hi,

Give complete informations.
Part values of the given sensor circuit, especially the OPAMP/comparator type, power supply...
* your schematic and exact part names.

Klaus

 

[FreshmanNewbie]

Hi,

Give complete informations.
Part values of the given sensor circuit, especially the OPAMP/comparator type, power supply...
* your schematic and exact part names.

Klaus

This is the sensor module that I am planning to order: https://www.electronicscomp.com/mq1...rMm10gUwKMi2KQg8_chYXkbmJrmgYAlBoCzxMQAvD_BwE

Would this be fine?

 

[FvM]

No problem to use voltage divider for analog output, resistance should be high enough to reduce sensor load R2 not too much. Digital output is redundant, connecting only Aout to ADC gives the same information. No DAC involved.

Aout range is most likely below 3.3 V in normal operation. Instead of a voltage divider, you can also use a simple series resistor that limits uC input current to allowed value in case Aout exceeds 3.3 V.

 

[FreshmanNewbie]

No problem to use voltage divider for analog output, resistance should be high enough to reduce sensor load R2 not too much. Digital output is redundant, connecting only Aout to ADC gives the same information. No DAC involved.

Aout range is most likely below 3.3 V in normal operation. Instead of a voltage divider, you can also use a simple series resistor that limits uC input current to allowed value in case Aout exceeds 3.3 V.

Can you please suggest resistor values for the voltage divider? Should it be same resistor values or different?

 

[FvM]

What is R2 value?

 

[FreshmanNewbie]

What is R2 value?

Can R2 be 100k? I am not sure on how to arrive. Or should 10k for R2 be fine? I haven't fixed any value.

 

[FvM]

MQ-135 datasheet is suggesting 10 to 47 kOhm for RL (R2).

https://www.olimex.com/Products/Components/Sensors/Gas/SNS-MQ135/resources/SNS-MQ135.pdf

 

[KlausST]

Hi,

Can R2 be 100k? I am not sure on how to arrive. Or should 10k for R2 be fine? I haven't fixed any value.

You showed a sensor module ... and a schematic.
R2 is shown on the schematic without value. But I guess R2 is assembled on the module.

We neither have the schematic vlues, nor can we check the module parts nor can we measure them.
But you ask us about the R2 value. What´s your idea: How can we know?

Are you expecting us to buy such a module and use an Ohm meter to measure the value?

Isn´t it more easy for you to check ... and way faster?

Klaus

 

[danadakk]

No problem to use voltage divider for analog output, resistance should be high enough to reduce sensor load R2 not too much. Digital output is redundant, connecting only Aout to ADC gives the same information. No DAC involved.

Aout range is most likely below 3.3 V in normal operation. Instead of a voltage divider, you can also use a simple series resistor that limits uC input current to allowed value in case Aout exceeds 3.3 V.

I may be out of date but most ADC/DAC specs do not discuss injection current
for normal spec considerations, mainly protection issues. Todays hi res ADCs and DACs
I would be nervous trying to meet accuracy with currents dumped into internal
supply routes, even worse into substrate (where does charge wind up, what regions
on die does it affect getting to ground....).


Regards, Dana.