G120 Analog Input Range

NETMF & Gadgeteer
1

The user manual (March 9, 2015) say’s the G120 has 10 bit analogs (0-1023).

AnalogInput.ReadRaw() is returning values from 0-4095, indicating the G120 has 12 bit analogs.

I assume the user manual is incorrect, right?

btw: My custom board has circuitry connecting the analog inputs to sensors that are 4-20mA, when I max the sensor out (20mA) I am seeing the digital analog count value = 4095

2

Voltage != current.

4095 when reading an analog line simply means the voltage is 3.3v.

3

Yes Brett… I fully understand how analogs work!
My circuitry converts current to volts, where 20mA = 3.3V.
At 3.3V on the analog pin, I am seeing a count = 4095.

The manual says the analogs are 10bit (0-1023)…but I am seeing 4095 (12bit).

I am asking for verification that the manual is incorrect?

4

so your “sensor” outputs 3.3v when the real sensor outputs 20mA. Great. Better to explain it that way :slight_smile:

So now the ONLY ask is for someone to confirm the G120 manual under-states the resolution for the ADC. Should be 12-bit not the 10-bit as documented.

5

Yes - just looking for confirmation from GHI.

The NXP LPC1788 User manual states:

12-bit Analog-to-Digital Converter (ADC) with input multiplexing among eight pins,
conversion rates up to 400 kHz, and multiple result registers.
The 12-bit ADC can be used with the GPDMA controller.

10-bit Digital-to-Analog Converter (DAC) with dedicated conversion timer and DMA
support

6

@ mhardy - You are correct. Analog input has 12 bit resolution. The manual has been updated.

7

Thanks for the verification and quick update to the user manual…

FYI,
The manual still has a misprint stating that analogs are 10-Bit, however.

Section:
1.3.G120 Module Key Features
.
.
.
.
8 10-Bit Analog Input

8

@ mhardy - Thanks again, it’s been fixed.