ads1115 is obfuscating a sign for values between 0 and -1mV in integer build

[paweljasinski]

Expected behavior

This is the case for integer build only Positive and negative values derived from volt and volt_dec in the range -1mV .. +1mV should be different for different polarization.

Actual behavior

As the voltage raises above the -1mV, the volt is 0 and volt_dec is positive.

raising about -1 mV

volt volt_dec dac -1 93 65466 -1 46 65469 0 984 65473 0 937 65476 0 875 65480

crossing zero

volt volt_dec dac 0 31 65534 0 15 65535 0 0 0 0 15 1 0 31 2

Workaround

Look at the dac value and correct the sign. or Do yourself the dac conversion. or Use floating build

Test code

id, scl, sda = 0, 1, 2
i2c.setup(id, sda, scl, i2c.SLOW)
ads1115.setup(ads1115.ADDR_GND)
ads1115.setting(ads1115.GAIN_0_512V, ads1115.DR_8SPS, ads1115.DIFF_0_1, ads1115.CONTINUOUS)

main_timer = tmr.create()
main_timer:alarm(1000, tmr.ALARM_AUTO, function()
    volt, volt_dec, adc = ads1115.read()
    print(volt, volt_dec, adc)
end)

NodeMCU version

dev branch, bee404c35890bbbcb4dd158991adb25621337a50

Hardware

wemos D1 with ads1015 (max gain, differential between in0 and in1, address pin grounded, 3.3V power).

[paweljasinski]

How about new set of specialized read functions. read_float - returns mV float and raw, in case of int build - error read_raw - returns only raw read_int - returns sign (-1,0,1), mV, uV and raw - this would be to mimic the existing one, but read_int could return just int32_t uV and raw

[devsaurus]

Not sure what's the best solution, but I would avoid specialized read functions to keep the API lean. Maybe something like

read() returns V, V_dec, raw and sign

• V is signed on float builds, unsigned on int builds.
• sign is nil on float and (-1,1) on int

The application can then adapt according to the value of sign:

if sign then
  -- int build
  print(string.format("%s%d.%03d", sign > 0 and "+" or "-", V, V_dec))
else
  -- float build
  -- just use V as it is
end

Guess we have the same issue with the ds18b20 module - missing sign between 0⁰C and -1⁰C?

[paweljasinski]

I have some of ds18b20 around. I can test it as well. If ds is also affected, should I create separate issue for ds, or can I piggybag here?

[devsaurus]

should I create separate issue for ds, or can I piggybag here?

I'd vote for a separate issue.