Wakeup sensor wiring

[hearttheart]

Hi,

I'm struggling a bit with the wiring for the wakup sensor functionality. Could you tell me which (if any) of the two is right? Please excuse the bad drawing...

[deleted wrong schematics to avoid confusion]

Thank you!

[Abasz]

Hi. Thanks for taking interest.

There is a bit of confusion here :)

Lets start with that "npm" is a package manager for javascript and nodejs, not a transistor. I suppose you meant "NPN". Any way.

First the reed do not need to go to the transistor as it is passive (reed is an actual physical switch). It goes one side directly to ground and the other to the ESp32 pin.

Second: npn is "low side switch" so it does not supply vcc, it "cuts" ground (in laymen's term). So you need to have emitter to ground and collector to the Hall sensor ground supply. the esp32 sensor on switch pin goes to base.

Third, I know that they claim that ky-024 modue is 3.3 volt ready but it generally uses an E49 linear hall sensor that where typical supply voltage is 5v (please see data sheet). Which means that 3.3v may not be sufficient to achieve full functionality. Not to mention that this board imitates digital signal via a voltage comperator, where the switching voltage is set by the potentiometer. I recommend first testing this (if you have not done already) without the sensor switch implementation, using 3.3v pin and the vcc out pin on the esp32 (which would be 5v if supplied from USB and between 3.8 and 4.2v if battery is used). Actually if this works well from 3.3v than you can ditch the transistor and supply vcc directly from the sensor on-switch pin (esp32 can supply around 20-30ma that should be enough for this hall to work). In this mode, when pin is high you supply the voltage to the board, when low you do not.

I had to implement this switching with npn transistor because I dont supply 3.3v (hall I use needs a higher, around 3.8-4 volts) but rather a higher voltage from the vcc which is not switchable.

if you stick to the can, use a mosfet its actually better as that does not current switch but voltage. I use 2n7000 in general. But if you have bjt only at hand that will work too.

Let me know if you have any further questions.

[hearttheart]

Thank you for the super fast response!

I'm planning a battery setup. If I understand correctly, the "safe bet" would be to use 5V output of the ESP32. Is my updated drawing (including the now corrected NPN/npm typo ;-) correct to be on the "safe side"?

[deleted wrong schematics to avoid confusion]

[Abasz]

it is. but the transistor is just a switch. but a digital one. it is controlled by the pin (low, 0v high 3.3v). Via the transistor you can switch higher voltage than the esp32 pin (e.g. 3.8, 4.2 or 5v or what ever the transistor is rated for).

But if the hall board works with 3.3 you can directly switch the board on and off. the rest (the reed setup and other things stay the same).

Basically the reed is just a sensing if there is some activity and tells the board to wake up. when the board wakes up and the sonsor witch pin goes high (starts supplying 3.3v). If your hall works from 3.3v than the hall can be fed directly. If your board needs more power than you need the transistor. Only difference in that setup is that vcc is directly connected sensor_on_switch and ground to groun (and you leave out transistor)

The reason behind all this is that a hall generally consumes 4ma so power to it needs to be turned off if you run it from battery. the reed do not consume any power because its a passive component. literally a switch. The reed is only detecting movement (passing of magnet) and sends a signal.

The transistor is just to step up the 3.3v to a higher voltage if the hall needs that (which your E49 might do but not necessarily, needs testing.).

I hope the above clarifies your questions.

[hearttheart]

Awesome - so, to sum it up:

[Abasz]

correct.

[hearttheart]

Update: Installed the the 3.3V setup (without the transistor/resistor). Stroke detection works fine.

[Abasz]

Very good. thanks for letting me know.