LPC1768 - Edge Trigger Pulses Over Count

[nmit.201]

Hi,

I have interfaced a pressure sensor which outputs a pulsed output whenever it senses any pressure.(Sensor output is amplified and is compared against a reference voltage and then fed to micro controller)

Sensor is fairly simple, and I have connected this to interrupt pin on LPC1768. I have configured it as an input pin with edge trigger enabled.

But I see number of counts counted inside the interrupt wrong. It is over counting these pulses and I am unable to find the reason for this, even after adding a small debounce for about 10ms this situation remains. Always count is higher than what it was supposed to be.

On a negative edge trigger ISR, Interrupts are disable, pending interrupts cleared, and a hardware timer is used as debounce which re-enabled back interrupt after debounce time.

Saw the output on a oscilloscope and pulses looks correct.

Any pointers?

Regards, Manjunath

 

[KlausST]

Hi,

You said you made everything correct.... but we can not verify this.

If you want us to help ... you need to give us the chance to help you by giving us informations we can verify.
* Sensor type and manufacturer
* used supply voltages
* schematic
* code
* expected values - and where does this expectation come from (datasheets, measurement device...)
* measured values
* scope pictures (with all the informations: measurement point at the schematic, X and Y setup...)

***

Sensor output is amplified and is compared against a reference voltage

For me this sounds as you need to measure duty cycle instead of pulse count.


Klaus