n87
January 3, 2025, 10:31am
61
I just did a write up on another thread for these hall effect sensors… or similar ones anyway… and I have already spent waaaay too much time on this today so I am going to shamelessly quote myself:
So I got one and mapped out the circuit noting that my sensor is different to either of the above, mine also has the ZTU module as it is the zigbee variant, either way this is what I came to after beeping it out (excuse the messy scribble):
U1 - HM6207 is the hall effect sensor, the modern fancy reed switch type component, most likely considerably cheaper and more robust, as this hall effect sensor has extra componentry to make it act like a reed switch (binary) instead of a hall effect sensor (how much attraction is in the air… or for the less whimsical, magnetic strength)
A glance at the resistor selection shows where all the battery draining is coming from, R6 on my board, a little 31ohm resistor.
R6 (31R)
Doing the maths to get the current:
R6 (31R)
Sooooo, this device was designed to sense a door, which in most cases is closed most of the time… so the 84mA expenditure when open is managable… buuut when you remove the magnet and use a reed switch to bring it low (closed), you are inverting that paradigm so it is using more current when your reed switch is open (for a normal reed switch, that would be the magnet not in range).
lots of words to say that ‘of course your battery is running low quick’.
Looking back at the circuit, I will be removing the transistor (Q3) and connecting my reed switch between its pin 3 and ground which will give me between (effectively) 0A and 1.3uA.
For anyone with a different board, beep yours out, it will most likely be the same overall circuit as I mapped out in the above pic, just with different labels and locations
Been alive for at least 6hrs so far and still at 100%, most of that was without magnet present but it is now functioning as my water meter sensor with a ~66% magnet present duty cycle, so will be a good test, if I remember I will update at some stage on the battery situation.
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