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as7421 problem with SMUX and GAIN configuration

TU1234

Hello,

I'm trying to configure the SMUX and ADC gain of the as7421, but the files explaining the configuration specified in the datasheet are missing and the company's support does not respond to my messages. I have already readout the specified RAM, but have not yet been able to recognize a pattern in the data that has already been entered in order to know where I have to write which values into the RAM. Has anyone solved a similar problem? I would appreciate it.

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  • +1

    doing this from my phone so please bear with me. I have spent a good month figuring this chip out. 


    They’re not explained in the datasheet. in fact, much is not explained. Did you know there are 5 LEDS? Not 4!!


    The smux is basically junk at boot up and needs to be set properly so there is no pattern.

    From what I’ve discovered through reversing it. The ASETUP ram locations are for the GAIN. ASETUPAB correspond to channels in the A and B integration and CD for the C and D integration. Both combined give the full 64 photodiodes. 

    You can set the values on eaxh cfg_ram between 0 and 8 giving a gain of 2^x. Setting 6 on CFG_RAM_x gives you a 64x Gain on photodiode x. I usually just fill all ram registers with the same value.

    SMUX is a bit harder. On each SMUX_x location. Each of the 32 CFG_RAM register represents 2 photodiodes as 4-bit nibbles. Each of the 4-bit nibbles can be set to either 1,2,3 or 4 representing each of the 4 available ADCs in each integration annd 0 as ground Each photodiode can be remapped to any integration cycle using this. However I am not quite sure which photodiode is mapped to which nibble.

    here is my procedure to set the smux with what works for me.

    go to each smux offset

    set all cfg_ram to zero

    then I use the configuration {0x21,0x21,0x21,0x21,0x43,0x43,0x43,0x43}

    set the offset to smux_a

    write the config only at cfg_ram_0 -> 7

    smux_b, write the config to 8->15

    smux_c, config 16-> 23

    smux_d config 24-> 31

    now the channel data read out is not in order of the datasheet PD listing and needs to be sorted correctly. I have some indices figured out. I will post them in a reply when I find them 

     

     

  • 0 in reply to primalfido

    Hello,

    I'm working on a sensor library for the AS7421 as well to use for a project and I was just wondering how you decided on the configuration ({0x21,0x21,0x21,0x21,0x43,0x43,0x43,0x43}) for the ram registers

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