Using the EN (enable) pin to power off the M6E from a Raspberry PI GPIO at shutdown

Sensors NFC & RFID
1

At the end of a race event, we will issue a “sudo shutdown now” to the Raspberry Pi which turns it completely off after an orderly shutdown. However, the M6E stays on until someone hits the power off switch, which they may forget about when busy dismantling their checkpoint equipment, arranging transportation for the volunteers, etc.

It is possible for the RPI to pull low the EN (enable) pin on the M6E before it shuts down but won’t the M6E power up again when the RPI turns itself off?

Thanks in advance

Pierre

2

It looks like pulling the EN line low will reset the module, not power it off…

Perhaps someone will share another known method, but I’ve used one of these https://www.sparkfun.com/products/11705 and a programmed shutdown with success if that’s an option in your design (we also have other styles of switches if you are using a different power config https://www.sparkfun.com/categories/314)

3

The enable line will power down the M6E. From the design document :

The ENABLE line (referred to as the SHUTDOWN line in the M6e) must be pulled HIGH or left unconnected in order for the module to be operational. To shut down the module, the line is set LOW or pulled to Ground. Switching from high to low to high is equivalent to performing a power cycle of the module. All internal components of the module are powered down when ENABLE is set LOW.

You can use a transistor circuit to keep the enable low after switching GPIO. see https://learn.sparkfun.com/tutorials/tr … i-switches

4

Thanks Paul, your answer is spot on as usual :slight_smile:

I will look at the transistor circuits and attempt to rig a “reverse” transistor switch powered directly by the battery:

  • As long as the RPI has power, it will keep a GPIO pin HIGH so that the M6E ENABLE Line is HIGH or unconnected through the transistor switch.

  • When the RPI no longer has power, its GPIO pin will therefore be LOW and the transistor switch connected to the battery will pull the M6E ENABLE Line to LOW, effectively powering down the M6E.

    • Sounds like an interesting little experiment !

    5

    the other alternative is a Relais…