APPLICATION NOTE
EZ-TILT- 1000
The EZ-TILT 1000TM is a low cost, high performance single chip solution for a dual axis tilt sensor angle conversion module. It provides the user with the ability to interface any dual axis electrolytic tilt sensor with a RS232 computer port This is the smallest solution that takes away from the user the burden of interfacing with a standard signal conditioner by replacing the need for synchronized clock, 8 bits analog to digital converter and microcomputer to generate the RS232 protocol. The EZ-TILT 1000TM has a set of commands to send various types of information to the host computer. The programmed micro-code in this customized chip decodes the signal output from the tilt sensor and separates the X and Y axis.
The algorithm was designed to work in a single as well as in dual axis modes. The EZ-TILT 1000TM incorporates an additional spare 8 bits analog to digital converter input which may be used for any external sensor input or correction signal. The communication with the EZ-TILT 1000TM is done through a 5Vdc logic levels RS232 interface. A simple circuit with MAX232 can change these signal levels into a standard RS232 type interface.
The speed of the port is directly proportional to the speed of the crystal oscillator. A 4 Mhz crystal will enable the port a rate of 9600 baud and a 8 Mhz crystal will enable the port a rate of 19200 baud. If the crystal is 8Mhz, the EZ-TILT 1000TM will send the output conversion to the host from 4 to 16 ms after receiving the READ command. The data is sent in 8 bits wide words with one stop bit, one start bit and no parity. Bytes are coded in ASCII format. For more details on the command format the user should refer to the appropriate table.
The theory of using the electrolytic tilt sensor generally prohibits DC current between any two electrodes of the sensor. The absolute maximum allowable DC current is 35nA. The excitation signals FR1P, FR1N, FR2P and FR2N provide short 5Vdc pulses to the four external electrodes of the tilt sensor. These signals are precisely generated to have a total DC current close to zero. The center electrode, the output of the sensor, is AC coupled through a 0.1microF capacitor. This signal is then referenced to the VSS (ground) by the output DC RESTORE. The input SENSOR IN is directly connected to the internal 8 bits analog to digital converter of the EZ-TILT 1000TM integrated circuit. The input GAIN allows the user to set the range of the internal analog to digital converter. The input OFFSET provides an offset if required by the user’s application. It is recommended to use voltage sources with output resistance lower than 10K for the GAIN and OFFSET inputs.
DC CHARACTERISTICS
Temperature -40C ----> 85C Industrial grade
Temperature -40C ----> 125C Automotive grade
Supply Voltage VDD 4.5V min
Supply Current IDD 4mA
Absolute Maximum Ratings
Ambient temperature:===========================-55C -----> 125C
Storage temperature:===========================-65C -----> 150C
Voltage on any pin with respect to VSS:============-0.6V to VDD +0.6V
Voltage on VDD with respect to VSS:==============0 to 7.5V
Max. Current out of VSS:========================150mA
Max. Current into VDD:==========================100mA
Max. Input clamping Current:======================+ / -20mA
Max. Output Current sunk by any pin:===============25mA
Max. Output Current sourced by pin:================20mA
Interface Commands
command=========output module===========description from Host
0============= x x CR===============read X axis
1============= x x CR===============read Y axis
2============== *===================reset CPU
3==================================not used
4==================================not used
5==================================not used
6===============x================== xread spare ADC input
Pin Description:
Reset (pin 4) : The reset pin starts all the internal algorithm. The EZ-TILT 1000TM takes less than 200mS to be ready to accept command from the host.
FR2N, FR2P, FR1P and FR1N (pin 8,9,10,11) : These pins provide the excitation pulses for the electrolytic sensor. The frequency is 125 and 250 Hz for a 8Mhz crystal. The width of the pulse is 200 microseconds.
Data in (pin 6) : This is the input of the RS232 internal port of the EZ-TILT 1000TM.
Data out (pin 7) : This is the output of the RS232 going to the host.
OSC2/CLKOUT (pin 15) : The EZ-TILT 1000TM can work with an external clock or a crystal oscillator
All the function of the IC are referenced to the value of this clock. It is recommended to use either a clock of 4Mhz or 8Mhz.
ADC0 (pin 17) : This is wired to one of input of the 8 bits analog digital converter.
SENSOR IN (pin 18) : This input is tied to the center electrode of the electrolytic sensor.
OFFSET (pin 1) : The voltage at this input can be between 0V and the voltage on the GAIN input (pin 2). The voltage is converted and then added to the output of the sensor. The operation is 2’s complement. For instance: if the voltage is 1/2 voltage on the GAIN input and sensor conversion output is 1/4 of the voltage of GAIN.
3F HEX + 80 HEX = BF HEX
If the two voltages are 1/2 the power supply.
80 HEX + 80HEX = 00 HEX
GAIN (pin 2): This input sets the voltage range of the converter. If the voltage is 3V the maximum voltage on the SENSOR IN pin is 3V. Note that if the GAIN voltage is lower than the VDD, then when the sensor is at null the output of the signal conditioner will higher than 80 HEX (255 / 2).
Upon POWERUP and RESET the IC performs a self test to confirm sensors presence in the circuit. If the sensor is PRESENT then the IC responds by sending a (*) character. If the sensor is ABSENT, then the IC responds by sending (!).
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ADVANCED ORIENTATION SYSTEMS, Inc. 2525 Brunswick Ave, Suite 205 LINDEN, NJ 07036, USA. Phone: 908-474-9595 Fax: 908-474-9090 sales@aositilt.com http://www.aositilt.com |