LIS3DH Interrupt Functionality

Hardware
1

Hi,
I have an Imp2 Dev board which has an LIS3DH on board. I want to use an interrupt feature of the LIS3DH IC (orientation detection) that is not implemented in the Electric imp Library for LIS3DH.

I was wondering if any one could point me to an Electric Imp code sample that uses I2C interrupts

Thanks

2

Isn’t the orientation direction just setting X/Y/Z thresholds appropriately and enabling those interrupts?

3

I was just about to post with the same answer. I was not reading the ST app note correctly. Thanks for the clarification @Hugo. I am trying to use one interrupt pin for wakeup and non-motion detection as shown in following article

http://www.ecnmag.com/article/2013/04/one-accelerometer-interrupt-pin-both-wakeup-and-non-motion-detection

If you look at Fig 2 in the article, the interrupt signal goes high when device is inactive for more than 5 seconds and then goes low when device is in motion. Would it be possible to interrupt this type of interrupt as DIGITAL_IN_WAKEUP and wake up the imp when the signal goes from low to high and high to low.

THanks

4

DIGITAL_IN_WAKEUP behavior is defined by the STM32 hardware, and is level sensitive on high levels only.

For an active low interrupt, this can be done with a PFET circuit. See Q30 in the Nora schematic here (“interrupt ORing circuit” box): https://electricimp.com/docs/attachments/hardware/reference/nora/impee-nora-sch.pdf

If you want an interrupt on both edges, you need to use an XOR gate & an RC. See this thread: https://discourse.electricimp.com/discussion/comment/20268/#Comment_20268 - if you want to make this more power efficient, buffer the signal first (so you can use a very weak pullup) before feeding it into the XOR with RC on one leg.

5

Here’s the low power version, though if you accelerometer has a push-pull output you don’t need the first XOR. Note you will need to connect RS to a GPIO so you can read the current state and RS_TRIGGER to Pin1 for wakeup.

6

Thanks a lot for the schematic guys. I will look into it. I had another request related to the LIS3DH class. I am looking at the library here and there are no public functions to access register values or write to registers. I want to turn on/off the High Pass Filter as well as look at orientation data.

What is the best way of adding the functions to the existing library and creating a new library for my use.

Thanks

7

Right now, you can do a pull request on the lib and if the changes are good then we’d pull them in and publish a new version. Currently, there’s no support for private libs, so you’d just have to pull the modified code into your device code.