A list of door sensor / reed sensor hacks! (Aqara, Xiaomi, others)

[n87]

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:

@n87

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.
As I am tired and cant remember all the standard voltage drops over standard comments… and I had my multimeter out… I measured the voltage drop over R6 and R0 when ‘door’ was open and closed

R6 (31R)
Closed: 0V
Open: 2.6V
R0 (2M4)
Closed: 0.1mV
Open: 3.13V

Doing the maths to get the current:

R6 (31R)
Closed: 0V = 0A
Open: 2.6V = 84mA
R0 (2M4)
Closed: 0.1mV = 5/8 of sfa
Open: 3.13V = 1.3uA

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).
With the upper limit of AAA capacity at 1200mAh, this would give you 14hrs not factoring in the overheads like the MC and radio

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.
Rough calculations gives this running for 105 years in its open state (not factoring in overheads of course)
I havent done mine yet… but it is on the list to do today… any minute now…

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.

[n87]

I purchased 2 different door/window sensors cause I read this thread first and people were having issues modding them… so I mapped out the other one, though it has been successfully modded above, I can see a neater way of doing it:

Board: ZD08Y-ZTU_V1.1 dated 2024-02-29

P1 is the wire attachment point, one is grounded, the other is mapped above.
both the external points and the hall effect sensor are connected to the same pin of the controller, so this is unfortunately not the second opening sensor being reported for this device (I was unable to find it at all, which I think has been mentioned above… it may just be a ghost… or lazy implementation)
The P1 part of the board (mapped above) is also unpopulated on my one.

Unlike my other door sensor, this one doesn’t have a stupid drain when open as its connected directly to the pin, but this also means that you need a pull up or down resistor instead of using existing.

I would suggest anyone looking to mod this one do the following (after you have confirmed that it is the same board by beeping it out):

• Attach wire for external sensor to P1, this is in a good place to feed out the hole in the back panel, is easy to solder and will be stronger.
• Bridge R10 (solder bridge or cut off resistor wire… or a 0ohm resistor if you are feeling fancy)
• Bridge Q1 between the R10 input and D7 output (careful not to bridge to VCC)
• Put a big resistor (1M would be my pick, but I haven’t tested this) in the R4 spot or in Q1 (between R10 and VCC)
  If you are half decent at soldering, you could use the resistor leg to bridge the Q1 pins by adding a sharp fold the right length, then put the other side to VCC

I am going to use this one as is, so please try at your own risk, trust but verify, if in doubt beep it out… other generic or humorous caveats…

[n87]

@n87

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.

Quick update on this as I am here: been running for around 20hrs, still at 100% battery