#13, M1S: Four-channel ADC
Function: Four-channel ADC
Form factor: M1S
Category: Input module
Special needs: +15V and -15V power (use Tibbit #12 to generate these voltages)
Power requirements: 5V/10mA, 15V/9mA, -15V/3.5mA (the aggregated consumption through Tibbit #12 is 66mA)
Mates with: #19, #20, #21 (limited use)
See also: #12, #14, #31, #43-1, #52, #53
This ADC Tibbit is based on the LTC2309 12-bit ADC with I2C interface. The Tibbit uses only four channels of this ADC. The analog front end of the module allows you to measure signals in the -10V to +10V range. All measurements are relative to the system ground.
Keep in mind that every time you read data out of the LTC2309 IC you are actually getting the previous conversion result. This may not be an issue when running a conversion loop for a single ADC channel. You will have to ignore the first result in these cases:
- Discard the first ADC result after the channel change. Only the second measurement will bring you the conversion data for the newly selected channel.
- Do the conversion twice and discard the first result when performing sporadic measurements. This way you will obtain the "current" data.
The LTC2309 ADC IC has 12-bit resolution. Tibbit #13 has an effective resolution of about 9 to 10 bits. This reduction is caused by system noise and other factors that affect measurement quality.
Combine this Tibbit with #20 (nine terminal blocks) or #19 (DB9M connector). It's not common but possible to use the latter for wiring into the ADC inputs.
Tibbit #21 (four terminal blocks) can also be used, but you will have to steal the ground elsewhere, as #21 doesn't have its own ground line and the ADC measures input voltages relative to the system ground.
There is one red and one yellow LED. The red LED is connected to the SCL line of the I2C interface, the yellow LED — to the SDA line.
The use of this Tibbit is illustrated by a Tibbo BASIC test project. You can find it here: https://github.com/tibbotech/CA-Test-Tibbits-13-14.