LMP91000: Setup for i2c and register values

Hi Dharmesh,

To confirm, you are currently testing with the LMP91000 evaluation module?

Jalen

Hi Jalen

Its my custom board.

At this stage i would like to read the internal temperature sensor, to insure ADC is setup correctly. 

For some reason, when i set the i2c i do not see a voltage being outputted from the IC.

At this stage, the sensor is not connected.  

Hi Jalen

Any further update to my case?

Thank you 

Hi Jalen

Thank you, 

I have setup the device as shown in example.

I am expecting an voltage to be outputted. Before i start setting my ADC in uC, i would like to see the voltage using volt meter. 

For some reason i am just seeing 0V, Should this be expected?

Hi Jalen

Please ignore the previous message, i have managed to get the device outputting a voltage, which reflect the temperature.

Tomorrow i will try to configure my sensor, as pass on any feedback

Thank You

Dharmesh,

Glad to hear you got it to work out.

What was the reason you were not seeing an output voltage?

Jalen

Hi Jalen

It was simply i2c packet structure when writing.

Hi Jalen

Been progressing with the sensor today.

For your reference the datasheet is attached.

On my board i had initially inserted the sensor wrong, as the counter and reference we swapped. Therefore i had to re solder the socket but on the other size of the board.

Mr register values for all the registers are the following

LOCK =0x00

TIACN=0x04

REFCN = 0x60

MODECN = 0x03

At this stage my voltage output 3.18V.

Is there away to confirm the sensor the LMP91000 is working correctly, before it used in the field as i do not want to be exposed to high levels of n02.

Should the voltage output increase or decrease as the ppm level increases?

Thanks

2480.0652.DS-0228 (SGX-4NO2) V1.pdf

HI Jalen

The voltage output seems to be 3.28V. I have tested the senors both indoors and outdoors, expecting some variation in levels, but nothing.

Is there anyway to check if the sensor it working correctly? Maybe using an oscilloscope? If so, what i should i be expecting?

Dharmesh,

Could you check to see if the output operates properly if you perform the test procedure in Section 8.2.2.1 of the LMP91000 datasheet using a single sensor?

Jalen

Hi Jalen

Thanks

So that i have understood, the testing,

So i keep the bias setting to a positive, and apply  a voltage to vref and keep changing the bias to see a change in the output?

The voltage being applied to will only be 3.3V.

Does the bias voltage need to be generated externally? Or is created in the IC  ,, if so how?

Thanks

Hi Jalen

How do i generate the low voltage, when my vref is 3.3V.

Is there an example i2c code to preform such test that i can see.

Hi Jalen

Yes i have found the register that sets the bias and made a function that tries to create the pulse as shown in the data sheet, but seems like the sensor could be damaged, as i am not seeing that pulse. 

Therefore i have order some extra sensors.

Just out curiosity does the bias sign of the sensor indicate if the voltage output goes from 0 to 3.3V or 3.3V to 0V?

Jalen

What i meant to ask was, as the sensor increases, how will the voltage signal from LMP91000 be represented, will it be from 0 to 3.3V or 3.3V to 0V?

Dharmesh,

I am still not sure what you mean by sensor increasing? Are you referring to something within the test procedure?

If not, a change in µA current of the sensor indicates a change in gas concentration. The LMP91000 processes the current and uses the linear TIA stage to convert the current to analog voltage. I suggest that you spend the time to characterize your gas sensor itself, we do not support the sensors so this is not something I can advise on.

Jalen

Sorry 

I meant, as the gas concentration increases in the atmosphere, would the voltage output range from 0 to 3.3V or 3.3v to 0?

Hi Jalen

I have communicated with the sensor company, in regards to this, but as i sensor is exposed to increments of gases, it is expected the vout would alter, but its seems VOUT remain at 3.28V. 

Is there a reason why this happens?

Dharmesh,

I have to point back to the test procedure in Section 8.2.2.1 of the LMP91000 datasheet. Have you confirmed this yet?'

Can you provide scope shots of the test?

Jalen

Hi Jalen

Ok, i will try that , just to be sure if i am correctly setting my code. 

To achieve 40mV bias, voltage if i am correct in to set

INT_Z to 00 -20%

BIAS 0100 --6%

Now that is set am i then pulsing between Sleep mode and  3-lead mode to see the output?

Dharmesh,

Yes you can perform the test as such.

Jalen

Should the polarity for the test be set to positive even though my sensor is negative?

Please use the negative bias option.

Jalen

This is the output pulse i am achieving.