### Little driver for the MCP3421 18bits ADC

Posted:

**Sat Feb 24, 2024 6:40 pm**Hi all,

Here you can find a very simple library for the ADC 18bits MCP3421.

This chip has a programmable resolution going from 12 to 18 bits coupled with a PGA (Programmable Gain Amplifier) with a gain of 1, 2, 4 or 8.

The chip has an input range of +-2.048V (+-2048mV) differential (it can measure positive and negative voltages).

Increasing the gain will increase the sensitivity but will reduce the scale (at gain=8 the scale will be 2048/8 = +-256mV).

The code contains two subroutines (SUBs): one that configure the chip (resolution and gain) and the other that read the value of the input signal.

In the code is shown how convert the value directly in millivolts, taking into account the resolution and the gain.

I hope it will be useful to someone.

Here you can find a very simple library for the ADC 18bits MCP3421.

This chip has a programmable resolution going from 12 to 18 bits coupled with a PGA (Programmable Gain Amplifier) with a gain of 1, 2, 4 or 8.

The chip has an input range of +-2.048V (+-2048mV) differential (it can measure positive and negative voltages).

Increasing the gain will increase the sensitivity but will reduce the scale (at gain=8 the scale will be 2048/8 = +-256mV).

The code contains two subroutines (SUBs): one that configure the chip (resolution and gain) and the other that read the value of the input signal.

In the code is shown how convert the value directly in millivolts, taking into account the resolution and the gain.

I hope it will be useful to someone.

Code: [Local Link Removed for Guests]

```
'ANNEX32 RDS MCP3421 library
SDA = 47
SCL = 21
I2C.SETUP SDA, SCL
' Set the resoluation and the gain
nb_bits = 18
gain = 1
mcp3421_config nb_bits, gain
v = 0
while 1
mcp3421_read v, nb_bits
'computes conversion to volts
' gain=1 @ 12 bits-> 1mv
' gain=1 @ 18bits -> 0.015625mv (1/64)
scale = 1 / (2^(nb_bits - 12))
mVolts = v * scale / gain
wlog mVolts; " mV"
pause 1000
wend
end
'read the value from the chip MPC3421
'nb_bits can be 12, 14, 16 or 18
'value returns the reading
sub mcp3421_read(value, nb_bits)
dim v(4)
i2c.reqfrom &h68, 3
for i = 1 to 3
v(i) = i2c.read
next i
select case nb_bits
case 12
value = (v(1) and &hf) << 8 or v(2)
if (value > 2048) then value = value - 4096
case 14
value = (v(1) and &h3f) << 8 or v(2)
if (value > 8192) then value = value - 16384
case 16
value = v(1) << 8 or v(2)
if (value > 32768) then value = value - 65536
case 18
value = (v(1) and &h3) << 16 or (v(2) << 8) or v(3)
if (value > 131072) then value = value - 262144
case else
value = 0
end select
'wlog v(1), v(2), v(3)
end sub
'configure the chip MPC3421
'nb_bits can be 12, 14, 16 or 18
'gain can be 1, 2, 4 or 8
sub mcp3421_config(nb_bits, gain)
local rate, pga
select case nb_bits
case 12 : rate = 0
case 14 : rate = 1
case 16 : rate = 2
case 18 : rate = 3
case else : rate = 0
end select
select case gain
case 1 : pga = 0
case 2 : pga = 1
case 4 : pga = 2
case 8 : pga = 3
case else : pga = 0
end select
i2c.begin &h68
i2c.write (rate <<2) or pga or &h10 ' continuous mode
i2c.end
end sub
```