MSP430F2618: Interrupts

Hello Amith,

Please refer to the MSP430x261x_ta examples from the MSP430F241x, MSP430F261x Code Examples package (SLAC151) and modify as necessary. Most of the differences involve "TA" nomenclature instead of "TA0" since the timer clock still resides on P1.0. However this code example seems insufficient as you should instead be using timer capture mode to evaluate the sensor pulse against a known clock frequency. The hall effect sensor chosen also operates at 5 V, since the MSP430 can only accept input below 3.6 V you will need to use a level translator accordingly.

Regards,
Ryan

I am using a Logic Level Converter to bring down the 5V as needed by the msp430.

The hardware I am using is from a private vendor which uses msp430f2618 board. It has a 14-pin configuration to connect the sensor and the configuration is as follows:

Name                                                  Pin No.

VCC                                                          1

GND                                                          2

P3.2/I2C_SCL                                           3

P3.1/I2C_SDA                                           4

P3.4/SPI_SIMO                                         5

P3.5/SPI_SOMI                                         6

P3.0/SPI_CLK                                           7

P4.4/SPI_CS1                                           8

P2.7/TA0/INT                                             9

P2.5/INT                                                    10

P3.6/RADIO_GPIO3/UART1TX                11

P3.7/UART1RX                                         12

P6.0/A0                                                     13

P6.6/A6/DAC0                                           14

If I am not wrong the output pin from the sensor has to be connected to the Pin 9 in my hardware. But most of the example codes use P1.0,2,3 and this hardware has P2.7 as the timer/interrupt pin I am getting confused.

Hi Amith,

I googled the sensor and came to this page:

It says two things about the output of the sensor: PWM output and output duty cycle of 50% (+/- 10%) with a pulse rate of 7.5 * l/min. This is no PWM in my eyes, so you do not need to measure the pulse width, only the frequency of the output. The "datasheet" again has some other values given - there is a table that says 120l/h results in a frequency of 16Hz, but 120l/h is 2l/min which would mean 8 * l/min. The documentation of the sensor is horrible, there are multiple supply voltage ranges given that say different things. And also another information about the pulse saying 7 * l/min...maybe the webiste decided to take the average of 7.5 ;-P

Anyway - the maximum flow through the sensor is 30l/min, so the maximum frequency is 30 * 7.5 = 225Hz (The website says "Pulses per Liter: 450" - don't know what that means). This is very slow. If you are not familiar with the capture mode of the timer, you can count the pulses with an incrementing variable inside a pin interrupt and look how many pulses were counted in one second or any other time period.

Dennis