ADPD188 light suppression outdoors

Hi,

I purchased the ADPD188 smoke sensor development board with ADPDUCZ microprocessor.

Using the wavetool GUI, I offset the sensor indoors, took the sensor outside and what I noticed was that there were negative spikes particularly in areas with bright light.

Using some mechanical light rejection, I was able to reduce the number of negative spikes to the point whereby it is no longer an issue. 

I also purchased the Mikroe Smoke2 Board, and wrote my own drivers to hook it up with the ESP WROOM via I2C. I followed the default configuration recommended in the datasheet when initialising the sensors.

However, what I've observed is that there are substantial continuous negative readings (not just spikes) when using the WROOM. It appears that the ambient light rejection is significantly poorer.

Do you have any idea why this might be the case? I used the recommended config in the ADPD188bi datasheet.

Based on the performance of the ADPA188+ADPDUCZ dev board, it is clear that the sensor itself has decent ambient light rejection, but using the WROOM with the recommended defaults is not getting me that.

Any help would be much appreciated. 

Cheers,

JM

  • 0
    •  Analog Employees 
    on Jun 28, 2021 6:55 PM

    Hello,

    In the absence of ambient light, and before you perform any offset correction, what are the clean air sensor readings on blue and IR channels? Negative spikes suggest that excess ambient light is causing the analog front end to saturate. Are you using the EVAL-CHAMBER with either of the boards? This chamber, which is designed by ADI, blocks ambient light from reaching the sensor.

    Regards,

    Revant

  • Thanks for the reply mate, and sorry for the late response. The clean air response is approximately 30 on one channel and 600 on the other before applying any offset. I am using the EVAL-CHAMBER for BOTH boards. For the better part, the chamber does do a good job, however when placed outside in sunlight, we begin to see negative spikes on BOTH boards (including the development board). The difference is that on the dev board, the negative spikes do not shut down the entire system, and the system is able to continue reacting to smoke input. With the Mikroe Smoke2 click Board, when a negative value is experienced, the value stays highly negative and does not recover.

    I originally thought it was a software issue as I am using a ESP8285 WIFI module to control the Mikroe Smoke2 click board, but what I found is that using the ESP8285 WIFI module with the same code with the Analog Devices Dev board, I get a stable response with the periodic negative spikes that does not affect overall performance. 

    This leads me to believe that it is a hardware issue which is causing the problem. There is some difference between the Mikroe Smoke2 click board and the Analog Devices Dev board that is causing the problems. I am not sure what the issue is, but some of the key differences I notice between the two boards are:

    - The AD dev board has a i2c EEPROM and an accelerometer

    - Some of the resistor/capacitor values are different

    - There are logic level converters on the Mikroe Smoke2 click board

    - The Mikroe Smoke2 click board uses ADPD188BI-ACE7RZ chip, but I'm not sure what the AD dev board uses.

    Could any of these hardware factors affect the performance?

    Thanks,

    JM

      

  • 0
    •  Analog Employees 
    on Aug 6, 2021 4:00 PM in reply to dkRok

    Hello,

    Is the device config that you are using the same as what is listed on the ADPD188BI datasheet page 42? If so, then the clean air value of 30 is too low. Do you see the negative spikes only in the presence of ambient light? It seems that the EVAL-CHAMBER isn't able to keep out the ambient light perfectly. 

    How big are the negative spikes and how frequently do they occur? Can you perform an ambient light experiment indoors by shining an LED whose intensity and modulation frequency that you can control? We typically use a green or white LED and control it with a function generator or a DC source meter. It's important to cover the test setup to keep any other light sources from interfering in the experiment. Please start with really small light intensity and slowly increase it until the sensor response changes.

    It is also possible that the ambient when doing this experiment light is affecting some other IC on the microcontroller boards. Can you cover everything other than the ADPD188BI sensor and chamber with black tape before taking the setup outside? 

    Regards,

    Revant