Report by evrim, 14 February,2007
The Hitachi H48C Tri-Axis Accelerometer is an integrated module that can sense gravitational (g) force of ±3g on three axes (X, Y, and Z). It is made by Hitachi Metals and available through Parallax.com They sell if for $39.95
The datasheet for H48C is found here and the documentation for the Parallax module is here .
Features:
- Measures ±3g on three axes simultaneously.
- For most app.s doesn't need calibration due to "compensation IC".
- Supply Voltage of +4.5V to 5.5V
- detects static tilt as well as movement.
- Small and breadboard friendly(YAY!): 0.7" x 0.8"
- Built -in temperature sensor. Module operation range -25 to 75 d. Celcius
- "Free Fall Detection" : Sends the pulse simultaneous 0g on all axes.
- Has standby mode
The table for the pin description is pretty straight forward.
(1) CLK Synchronous clock input
(2) DIO Bi-directional data to/from host
(3) Vss ground
(4) Zero-G "Free-fall" output; active-high
(5) CS\ Chip select input; active-low
(6) Vdd +5V
How it Works
H48C provides voltage output to the built in ADC on the module. With Pics this data can be read with SHIFTOUT or in Arduino with PulseIn command.
To convert that voltage value to gravitational force we can use following formula.
G=((axis-vRef)/4095)x 3.3/ 0.3663)
Here 4095 is the maximum output count from ADC channel. 3.3 is the H48C supply voltage, and 0.3663 is the H48C output voltage for 1g(when operating at 3.3)
The only thing that I don't understand is that what is the vRef. I understand that it is the reference but how do we tell the sensor to give me the reference voltage and the axis voltage. Datasheet doesn't say what message to send to get vRef.
