Generally used to monitor rolling stock's acceleration profile or engine's vibrations, Aloha can be equipped with an external accelerometer extension.
Inside the extension resides the sensor itself, along with other components to be compatible with different digital interfaces of Aloha. The sensor is Analog Device's ADXL355: a low-noise, low-power, 3 axes accelerometer with a +/- 8g full-scale.
The extension is intended to be used with the 5VDC supply provided by Aloha, be it from its upper front connector or from one of the back IDC connectors:
The extension can also be powered from an external 5VDC power supply with the same voltage reference as Aloha. It must be able to deliver a minimum of 5mA:
The accelerometer extension can be connected to Aloha through one of the next four digital interfaces: EXT_SPI, I2C0, I2C1 and BUF_I2C.
This interface is a standard 4-wire SPI bus with the MOSI, MISO, SCLK and CS (chip select) signals. The EXT_SPI bus is comprised of two chip select signals, CS0 and CS1. Either can be connected to the extension's CS signal:
I2C0 and I2C1
Either can be used as a standard 2-wire I2C bus with SDA and SCL signals:
Contrary to the previous interfaces, the buffered I2C is to be used when the accelerometer extension must be installed more than a few cm away from Aloha. For this purpose, the buffered I2C interface embeds a line driver extending the range to a few meters:
Furthermore, the user can choose between a 3V3 or 5V voltage levels for the data and clock lines through the exposed VSEL switch on Aloha's front panel and inner switch of the accelerometer extension:
N.B.: The voltage level switches must be set in the same configuration (5V with 5V or 3V3 with 3V3). Otherwise, damage can be delt to the extension's inner power supply.
N.B.: Because of the line driver, the BUF_I2C bus cannot be used with standard I2C busses.
The accelerometer extension is packaged in an 80.4L x 50.4W x 35H mm IP65 ABS enclosure with two wall mounting flanges and an IP65 4-pole female circular connector on the top lid. If the BUF_I2C bus is to be used, a 5-meter twisted pairs shielded cable with an IP65 4-pole male circular connector can be provided.