ARD-LTC1863 / ARD-LTC1867 Hardware Reference
- JP1 - I2C Pull-up Enable
- JP2 - I2C Pin Selection
- JP3 - Onboard 5V Linear Regulator Enable
- JP4 & JP5 - 24AA025E48 EEPROM I2C Address
- JP6 - Chip Select Digital IO Pin Mapping
JP1 - I2C Pull-ups
The I2C bus depends upon a set of pull-up resistors to function correctly. Each I2C bus should have one and only one set of pull-ups enabled. The ARD-LTC1863 / ARD-LTC1867 includes a set of 2k pull-up resistors that can be enabled by jumpering JP1A and JP1B. Note that most Arduino boards do not provide I2C pullups, so at least one board connected to I2C must provide them. To enable, place a jumper across pins 1&2 and across pins 3&4.
JP2 - I2C Pin Selection
Not all Arduinos provide I2C on the same pins. With the Rev 3 hardware designs, there are now a dedicated set of pins above AREF and GND marked "SDA" and "SCL". If you see those on your board, then place jumpers between pins 3-5 and 4-6 on JP2 to connect the I2C bus to them.
If you board does not have explicit SDA and SCL pins, then most likely they're shared with pins A4 and A5. Place jumpers between pins 1-3 and 2-4 to select those instead.
JP3 - Onboard 5V Linear Regulator Enable
To free the LTC1863 / LTC1867 from any noise on the Arduino's 5V supply caused by the AVR or other shields, the ARD-LTC1863 / ARD-LTC1867 includes an onboard 78L05 regulator coming from the Arduino's "VIN" pin. If you are powering the Arduino with >8VDC via the power jack, you can use the onboard 5V regulator to provide nice quiet power by jumpering pins 3-4 of JP3.
If you are powering the Arduino off of the 5V provided by USB or via some other means that does not place >8VDC on the VIN pin, then the regulator will not work and must not be used. JP3 must be placed between pins 1-2 in this case.
JP4 & JP5 - 24AA025E48 EEPROM I2C Address
Each device on the I2C bus must have a unique device address. The 24AA025E48 EEPROM that provides both non-volatile storage and the globally unique ID number has four possible addresses depending on how JP4 and JP5 are set. Each may be set high (no jumper) or low (jumper in place). Please refer to the Figure 5-2 in the 24AA025E48 datasheet (we use the SOT-23 version, so A2 is always '0' - otherwise JP5 is A1 and JP4 is A0) or the Ard1863 library header for corresponding address values.
JP6 - LTC1863/1867 Chip Select Digital IO Pin Mapping
In order for the Arduino to address the LTC1863 / LTC1867, it needs a "chip select" pin. Normally this is digital IO D3 (pins 1&2 jumpered), but Leonardos share D3 with the SCL line needed for I2C communication. If you have a conflict on D3, you can set the jumper to pins 3&4, and this will use digital IO D8.
If you do use D8, be sure to pass in the correct pin in the begin() function in the Ard1863 library.
The useful measuring range of the inputs is 0-4.096V in single-ended mode, and a +/-2.048V in differential mode. Be careful of common mode limits, however. Inputs have an absolute maximum common mode limit of -0.3V to +0.3V above Vcc (nominally 5V) before damage to the part will occur, so while the differential inputs can have -2.048V between them, neither side of the input may violate the limit of -0.3V to 5.3V without damaging the part.
To eliminate any possibility of introducing gain or offset errors from buffering, the pins of the LTC1863 / LTC1867 are brought directly to the terminal headers. Thus, please be careful when handling and using the board. Errant electrostatic discharge or voltages applied outside the absolute maximum limits specified in the datasheet can cause damage rather quickly.