#52, M2S: Four-Channel Isolated ±10V ADC
Function: Four-channel isolated ±10V ADC
Form factor: M2T
Category: Input module
Special needs: --- (isolated power is generated internally)
Power requirements: 5V/100mA
See also: #13, #31, #43-1, #43-2, #53
Details
This analog-to-digital converter (ADC) Tibbit uses four ADC1100 16-bit analog-to-digital converter ICs. All four converters are used in the differential mode (i.e., the (+) and (–) lines of each ADC are exposed to the outside world).
The ADCs are connected to a PIC16F1824 microcontroller. The PIC microcontroller interfaces the ADCs to the main CPU of the host Tibbo Project PCB (TPP) and also stores the calibration data in its EEPROM. This calibration data is written into the EEPROM during manufacturing, when each ADC channel is individually tested and calibrated. The calibration data reduces the full-scale error caused by the imperfection of ADC input divider stages (not shown in the diagram).
To lower noise and improve resolution, this Tibbit has its own isolated power domain.
ADC characteristics:
- Each channel measures signals from –10V to +10V.
- With our official Tibbo BASIC library (performing the data correction using the calibration data), you can measure the voltage level on one channel in about 140ms.
- Effective flicker-free resolution is better than 13 bits.
- Zero-offset error is within 0.005% of the input signal's scale (20V, from –10V to +10V).
- Full-scale nonlinearity error is about 1% (after the range correction).
Combine this Tibbit with #20 (nine terminal blocks) or #19 (DB9M connector). It's possible, but not common, to use the latter for wiring into the ADC's inputs.
LEDs
There are two red, one yellow, and one green LED. The first red LED is connected to the SCL line of the I²C interface, while the second one is connected to the –RST line of the PIC microcontroller. The yellow LED is connected to the SDA line of the I²C interface. The green LED is on the –INT line.
Sample Project
The use of Tibbit #52 is illustrated by a Tibbo BASIC test project. You can find it here: https://github.com/tibbotech/CA-Test-Tibbit-52.