TLV2404 low power PIR sensor interface

Hello Hansen,

If you are interfacing the PIR to an MCU, you can tie it directly to an ADC channel.

Thanks,

Hello greenja ,

Thanks for your reply , I found this article http://www.ti.com/lit/an/slaa283a/slaa283a.pdf about interfacing directly to ADC.Were you referring to this?

The MSP430F2013 has 2KB of flash and does not have a serial port which would be required for my application.

I had decided to use the MSP430F5510 as it has more flash and a USB interface.

Do you have any other suggestion or inputs on the analog design

Thanks

A good application note I came across

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/DM00096551.pdf

Hello Hansen,

That wasn't the exact document, but it is a good one.  No comments on your analog design other than if you really want to conserver power then you could only enable power to the PIR and OP Amp when taking a reading.  Otherwise both devices are off and consuming no power.

The MSP430F5510 has an ADC, why can't you use it?  Depending on the voltage required by the PIR you could use a port pin to power it or a transistor it 5V is required.

Thanks,

There is also this one http://www.ti.com/lit/pdf/slaa061.

The PIR takes about 15 seconds to warm up hence I cannot shut it out, as it will affect overall response.Although I will keep the option for shutting of the OPAMP for future optimization.

The MSP430F5510 does not have a PGA , the signal from the PIR is a low voltage AC riding over a DC level which will not be visible to a ADC without appropriate filtering and amplification.

Thanks

Then it looks like you will have to go with the analog version.  There is a schematic similar to yours from the PIR manufacturer.  It also uses the LM324, but you should be able to replace it with a low power OP Amp.

http://www.micropik.com/PDF/D203B-e.pdf

I hope someone else can give you the best solution for an OP a Amp, otherwise, the parametric search is an option.

Thanks,

HI,

I was wondering if its OK to connect comparator output of 5V directly to MSP430 inputs using 100K series resistor?

The series resistor would limit the current flowing from the port pin protection diodes

Regards,

H

Hello Hansen,

It would limit the current, but not the voltage.  If the MSP430 is a 3.3 volt device, then you would have to set up a voltage divider circuit so that the 5V is scaled to 3.3V.  Or whatever the HiGH Level voltage for a logic 1 is for the device, probably 1.8V.  So a two 100K ohm resistor voltage divider should work.

Thanks,

TI has released a TI Design that covers this topic.  You can find more information about it here.