Recreating a low-power door lock

[dakhnod]

This discussion is supposed to aid with the process of recreating the smart door lock from https://www.hackster.io/dakhnod/battery-powered-door-lock-opener-2aada7.

@crozo5, how's progress?

[dakhnod]

Btw. the PWM output for controlling servos should be in the range of 1000-2000, I believe, since those are uS.

[crozo5]

As I said, I'm quite a novice, so I think I'll need a lot of help 😅

This is my idea for the connections, it's very likely I'm doing things wrong:

My idea is to use a MOSFET module to completely shut down the servomotor when not in use and wake it up only when necessary, to save battery life.

I have questions about programming both https://ble.nullco.de/ and the gpioASM part. For your example, you used the following:

label start
write_digital 100
sleep_ms 1
write_digital 110
sleep_ms 1
jump_count start 540
write_digital 000

But as you say, the PWM output for controlling servos should be in the range of 1000-2000, but I don't know how to adapt it in code.

And I don't see Nice!Nano Promicro on the list of boards:

[dakhnod]

You're right, the nice!nano is not on the list. Just chose a pin for the PWM output and set it to analog output.

[crozo5]

Hello again, the project is progressing little by little.

I share a video of a small test sequence:

1811d3d8-478b-4f51-bdd0-f670698664f1.MP4

This is the sequence in https://ble.nullco.de/:

With 1000 uS the servomotor rotates clockwise, at 1500 uS it stops and at 2000 uS it rotates counterclockwise.

My purpose, as you said before, is to control everything from Home Assistant, using an ESP32 as a Border Router, in Home Assistant it is very easy to do using them as a Bluetooth Proxy (https://esphome.io/projects/?type=bluetooth). My question is whether with the Bluetooth proxy in active mode, the ESP32 will automatically detect the Promicro NRF52840 board.

If I'm not mistaken, it's the same thing you do, but I don't know what firmware you use on the ESP32, I use Esphome:

Another question I have is about energy consumption. Do you use anything to optimize consumption?
From what I had read, the nRF52840 had two sleep modes, “System On” and “System Off”. The former being a light sleep and the latter being a deep sleep. “System On” puts the chip to sleep, but it’s still awake. From Nordics documentation, even “System On” requires only a few µA. I think it's also a mode the chip automatically goes into when it detects you're not doing anything.

Thanks.

[dakhnod]

Heyo good job so far!

I am personally using my ble mqtt bridge, also somewhere on my GitHub.

I am thinking a lot about HA, not sure it supports the Automation IO protocol for now.
I'm sure it doesn't support gpioASM, but maybe I can write a plugin for that.

Regarding power consumption:
I think stepping up 3.7V and stepping it back down on the chip is not the most efficient thing.

I personally use AA batteries, since those spit out 3v.
To get real efficiency, you have to feed the 3V in through a stupid test pad on the promicro.
You'll find notes on that in the docs/boards folder.

Last thing to consider it the leakage through the PWM pin when the servo is shut down, you'll have to measure that, but we'll find a solution.

Lastly, generating PWM consumes a lot of power, so make sure so reset the PWM signal to 0 when not in use.

BLEnky goes into system on mode by default.
The only thing you could tweak are connection parameters, but those are pretty Power-efficient by default.

[dakhnod]

Heyo, how's progress so far?

There are some new considerations to make regarding power consumption, as stated in the pro micro documents.

How big is your battery?

[crozo5]

I haven't been able to make much progress since last time; I haven't had much time.

I think I'll follow your advice and use AA batteries, about 8 maybe. I understand that to get 3V, I must connect two groups of 4 batteries, each group connected in parallel and between the two groups connected in series, to get 3V.
The goal is to have to change the batteries once a year; I could add more AA batteries if necessary. Would it be possible to add an INA219 module to take battery voltage readings every x period of time to know when to change them? Could I read the measurements with the Blenky firmware?

I will follow the guide you made here: https://github.com/dakhnod/BLEnky/blob/main/docs/boards/PRO_MICRO.md

On the other hand, I would like to know if it is possible to deactivate the LED on the top left that keeps flashing blue, which I understand must increase consumption.

[dakhnod]

the configuration you described is called 2s4p or 4p2s, not sure about the order.
With a capacity of 2000mah per AA, this would give you 8000mAh in total, so 8000mAh / 0.03mAh = 266666H = 11111 Days = 30 Years of BLE connection. Half that for good measure.
If the servo consumes 500mAh if can spin continously for 16 hours. If it does that for one minute a day, you can get 960 days out of that, or three years. Again, half that for good measure.
So your setup should last for over a year.

The LED is disabled if you apply 3V over something else than USB.

I am personally using a stepper motor, and I can just disable the driver, which makes the spring in the door handle automatically unwind the string from the axis.

This will probably not work for a servo, so you have to thing abour some synchronization method like an endstop.

If you feed in voltage directly to the nRF51, as should be the case through the pad on the back, BLEnky provides you with the battery percentage and voltage already.

[crozo5]

Sorry for taking so long, but I've been short on time for this lately.

I've modified the wiring following your advice. In test mode, I used a 2P2S battery configuration, so I'm feeding a maximum of 3.6V through the VDD and GND pins when the batteries are fully charged, and surprisingly, I can feed the servomotor 4.8V without any resistors or converters.
This way, the blue LED I mentioned earlier no longer lights up, and I can save even more battery life.

2025-04-29.19.33.56.mp4

At this point, I have two options: either you give the wonderful world of Home Assistant a try and avoid having to learn how to use your MQTT BLE bridge (in Home Assistant, I use the Mosquitto broker addon for MQTT).

Or, learn how to use your MQTT BLE bridge and try to integrate it somehow with Home Assistant so I can control the servomotor with the mobile app and not rely solely on the web https://ble.nullco.de/.

*Another question, about the https://ble.nullco.de/, is the "Device battery level" value real with the connection I have made?

[dakhnod]

@crozo5 The battery level relies on the input voltage between 1.8 and 3.0V and is only reliable if you feed the voltage directly to the nRF through the back via.
Using something like "nRF Connect" app, you can even read out the battery voltage by reading the characteristic and the descriptor.

I am not against HomeAssistant, I just haven't gotten around to tapping into it. It would surely be an important milestone.

For now, the MQTT bridge should be a matter of flashing the firmware, configuring WiFi, adding the MAC address to the config and posting the right MQTT message.

This will probably not work for a servo, so you have to thing abour some synchronization method like an endstop.

Sidenote: have you solved the synchronization I mentioned somehow?

[crozo5]

@crozo5 The battery level relies on the input voltage between 1.8 and 3.0V and is only reliable if you feed the voltage directly to the nRF through the back via.
Using something like "nRF Connect" app, you can even read out the battery voltage by reading the characteristic and the descriptor.

I have connected the power supply through the back of the board, I have installed the nRF Connect app and I see that a feature called Battery Level appears with a value of 86. Does this mean that the battery is at 86%?

My idea is to make a smart lock more similar to the one shown in this video https://youtu.be/4-wtu9toda0?si=vScgk6bwLyE21__O, but directly using a board with Bluetooth such as the PicoPro NRF52840 or the Xiao BLE, instead of using an ESP8266 or ESP32.

For now, the MQTT bridge should be a matter of flashing the firmware, configuring WiFi, adding the MAC address to the config and posting the right MQTT message.

Where can I find the firmware you are referring to?

Thanks

[dakhnod]

Heyo, I am referring to this project: https://github.com/dakhnod/esp32-ble2mqtt.

Still, how are you planning on solving the synchronization?

[crozo5]

I finally got it working with Home Assistant, using Esphome and an esp32 as a BLE border router. I'm sharing the code in case it helps anyone:

Esphome Code:

esphome:
  name: esphome-web-9ddf20
  friendly_name: ESP32 Proxy

esp32:
  board: esp32dev
  framework:
    type: arduino

# Enable logging
logger:

# Enable Home Assistant API
api:

ota:
  platform: esphome

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "XXXXXX"
    password: "XXXXXX"

captive_portal:

esp32_ble_tracker: 

ble_client:
  - mac_address: XX:XX:XX:XX:XX:XX # Replace with the MAC of your NRF52840
    on_connect:
      then:
        - component.update: bateria_nrf52_sensor
        - logger.log: "NRF52_Lock: Connected."
    on_disconnect:
      then:
        - logger.log: "NRF52_Lock: Disconnected."
    id: nrf52_lock

switch:
  - platform: ble_client
    ble_client_id: nrf52_lock
    name: "Conection Lock NRF52"

sensor:
  - platform: ble_client
    type: characteristic
    ble_client_id: nrf52_lock
    id: bateria_nrf52_sensor
    name: "Bateria NRF52 Lock"
    service_uuid: "180F"
    characteristic_uuid: "2A19"
    icon: 'mdi:battery'
    unit_of_measurement: "%"
    update_interval: 1h

lock:
  - platform: template
    name: "SmartLock NRF52"
    id: home_assistant_lock
    lock_action:
      - ble_client.ble_write:
          id: nrf52_lock
          service_uuid: "1815"
          characteristic_uuid: "2A58"
          value: [0xE8, 0x03] # Equivalent to 1000 (us)
      - delay: 4s
      - ble_client.ble_write:
          id: nrf52_lock
          service_uuid: "1815"
          characteristic_uuid: "2A58"
          value: [0x00, 0x00] # Equivalent to 0 (us)

    unlock_action:
      - ble_client.ble_write:
          id: nrf52_lock
          service_uuid: "1815"
          characteristic_uuid: "2A58" 
          value: [0xD0, 0x07] # Equivalent to 2000 (us)
      - delay: 4s
      - ble_client.ble_write:
          id: nrf52_lock
          service_uuid: "1815"
          characteristic_uuid: "2A58"
          value: [0x00, 0x00] # Equivalent to 0 (us)

I would like to know if there is any way to implement a PIN or Passkey with your firmware when you try to link the NRF52, to give it greater security.

I don't know if I understand you very well about the synchronization issue, at the moment what I have is using a time delay.

[dakhnod]

There is indeed a way to implement a pin code, but:

1. You would have to compile the firmware yourself
2. I am not sure how to apply the PIN using HA

Also, I just saw that you are sending the motor start signal first, then you wait, then you send the motor stop signal.

While this might mostly work, you introduce jitter and the risk of a connection breakup during the delay.

Since you created the sequence on ble.nullco.de already anyway, you could just copy the bytes from the first packet and send them directly.
This way you only send a single packet for the motor start, delay, and motor stop.

The synchronization issue I meant is this:

Imagine the servo spinning a bit faster in one direction than in the other.
This way, by just waiting 4s, your servo will spin further in one direction than the other, and you will have a drift over time.
You could solve this by some tuning and resetting the servo every few weeks, I would assume.

Anyways, good job! That was quite some progress!

[crozo5]

There is indeed a way to implement a pin code, but:

1. You would have to compile the firmware yourself

I don't think I have enough level to compile it by myself 😅 hehehe

2. I am not sure how to apply the PIN using HA

In Home Assistant (with Esphome) it's very easy, you just have to add this code:

ble_client:
  - mac_address: XX:XX:XX:XX:XX:XX
    id: ble_itag
    on_passkey_request:
      then:
        - ble_client.passkey_reply:
            id: ble_itag
            passkey: 123456 # This is the PIN you have set

Note: passkey: 123456 is the PIN that must match the one configured on your BLE device.

Since you created the sequence on ble.nullco.de already anyway, you could just copy the bytes from the first packet and send them directly.

Where and how can I extract the bytes?

Thanks

[dakhnod]

On the site there should be a section "gpioASM upload".
There you should see your sequence reflected as bytes.
You need to send the bytes of the first packet to UUID b1190001-2a74-d5a2-784f-c1cdb3862ab0.

[dakhnod]

Also, you can shoot me an email to "dakhnod@gmail.com" and we can figure out the PIN thing.

[crozo5]

On the site there should be a section "gpioASM upload".
There you should see your sequence reflected as bytes.
You need to send the bytes of the first packet to UUID b1190001-2a74-d5a2-784f-c1cdb3862ab0.

Oooh much better! Thanks, Using "Output Sequence" makes everything much cleaner:

lock:
  - platform: template 
    name: "SmartLock NRF52"
    id: home_assistant_lock
    lock_action:
      - ble_client.ble_write:
          id: nrf52_lock # ID del ble_client
          service_uuid: "B1190000-2A74-D5A2-784F-C1CDB3862AB0"
          characteristic_uuid: "B1190001-2A74-D5A2-784F-C1CDB3862AB0" # UUID de comando
          value: [0x01, 0xf0, 0x10, 0xe8, 0x03, 0x20, 0xf0, 0x2e, 0x01, 0xf0, 0x10, 0x00, 0x00, 0x20, 0xe8, 0x07] # OUTPUT SEQUENCE

Note: value: [0x01, 0xf0, 0x10, 0xe8, 0x03, 0x20, 0xf0, 0x2e, 0x01, 0xf0, 0x10, 0x00, 0x00, 0x20, 0xe8, 0x07] is the result of "gpioASM upload" section: "01f010e80320f02e01f010000020e807"

One question, Is it possible to abruptly stop a launched sequence, if necessary? Or launch another sequence that overlaps the previous one?

Thanks

[dakhnod]

Nice! Good job. You can stop the running sequence by sending another, empty one. Or Send a sequence that only resets the PWM to 0.

[dakhnod]

For everyone reading along: I have provided @crozo5 with a firmware containing his desired Pin.

While the firmware works with the nRF Connect App and asks for the Pin, ESPHome seems to have issues with the Pin.

That could be related to the bonding type which, I believe, is BT classis and not BLE with BLEnky.

[crozo5]

To improve the Smart Lock project, I would like to connect a digital (I2C) current measurement sensor like the INA219 so that, in case the servo motor gets stuck or if I have previously opened the lock manually, leaving the lock in an intermediate position, neither completely closed (2 turns of the key counterclockwise) nor completely open (2 turns of the key clockwise), and I activate it to open or close the lock, it does not force the motor once it reaches the opening or closing stop.

Is there a way with four firmware to read the Ampere measurements?

[dakhnod]

This one is tricky. While the nRF51 is obviously able to communicate via I2C, BLEnky currently only supports the BMA400 accelerometer, which is of little use to you.

You may be able to use some analog measurement circuitry and read the signal through a gpio, and use a potentiometer to calibrate the threshold.

I assume that using an endstop is not an option since you are doing multiple rotations?

[dakhnod]

Still, a slip clutch sounds like the easiest solution.
Implementing the I2C protocol for the INA219 is quite a chunk of work.

I have also not been able to find out if the INA219 supports pin interrupts.

[crozo5]

Something like that? https://eu.store.bambulab.com/products/9g-servo-motor-with-clutch-protection?id=47978193486172

2025-05-22.19.38.11.mp4

This seems like a simple solution to my problem. With the clutch protection, it seems like it would protect the servo from possible overloads.

The problem is that I'm not finding any compatible one for my MG996R servo.

[dakhnod]

Could you send a photo of your lock setup? Maybe I can come up with something

[crozo5]

I'm waiting to buy a 3D printer to be able to put it all together, but the idea is to make something inspired by this video:

My setup is like the image I shared at the beginning of the comments, but with 8 AA batteries connected in 4p2s and without the voltage regulator.

[crozo5]

Finally, I've found a module that does exactly what I wanted. It measures the motor current, and if it detects that the motor is stalling (it increases the current), which you can adjust with a potentiometer, it sends a digital output that you can read with the MicroPro and Blenky.

The module is called WCS2702

I think it is also possible to do it with the INA301 module

[crozo5]

This is my progress on this project, I continue testing with different engines and drivers. In previous comments I have already shown how I did it with a servo motor, now I will show how I will do it with a Nema14 stepper motor and with a N20 DC motor.

1) Nema14 Stepper Motor:

In this case I use 3 16340 batteries in series, with which I get about 11.1V to power the stepper motor, then I use an MP1584 to go from 11.1V to 3.3V to power the MicroPro board, the A4988 driver and the WCS2702 module that I use to detect if the motor is stuck.

This would be the GPIOASM code that I use:

Lock:

label main_loop
jump_match_any give_the_pulse 1
write_digital 0111
sleep_ms 3
write_digital 101
sleep_ms 3
jump_count main_loop 2800
label give_the_pulse
label stop
write_digital 0000

Unlock:

label main_loop
jump_match_any give_the_pulse 1
write_digital 0011
sleep_ms 3
write_digital 0001
sleep_ms 3
jump_count main_loop 2800
label give_the_pulse
label stop
write_digital 0000

0.13 --> Digital Output (LDO OFF ProMicro)
0.17 --> Digital Input (WCS2702)
0.20 --> Digital Output (Direction A4988)
0.22 --> Digital Output (Step A4988)
0.24 --> Digital Output (Sleep + Reset A4988)

2) N20 DC Motor:

In this case, I used an 800mAh 3.7V LipO battery to power everything. I used the L298N Mini driver to control the DC motor, and the WCS2702 to detect stalling.

This would be the GPIOASM code that I use:

Lock:

label main_loop
jump_match_any give_the_pulse 1
write_digital 110
sleep_ms 3
jump_count main_loop 2800
label give_the_pulse
label stop
write_digital 000

Unlock:

label main_loop
jump_match_any give_the_pulse 1
write_digital 101
sleep_ms 3
jump_count main_loop 2800
label give_the_pulse
label stop
write_digital 000

0.02 --> Digital Input (WCS2702)
0.13 --> Digital Output (LDO ON ProMicro)
0.29 --> Digital Output (IN2 L298N)
0.31 --> Digital Output (IN1 L298N)

[dakhnod]

Nice, thanks for sharing!

[crozo5]

Another improvement for this project that I would like to implement is to create a wireless keyboard with a fingerprint sensor.

Matrix Keypad:

R503 Capacitive Fingerprint Reader:

I saw in your video that you also use a fingerprint sensor to open the lock, I saw the link to the project that you left in the description, but I don't understand it much 😅 hehehe. Could you give me a hand? I'd like to do it with another ProMicro board.