---
active: false
tags:
  - project
created: 2025-05-30
completed: 2025-06-21
---
## Goal

Create door latches that use servos with more torque so that the latch will open under side pressure.

- Must be able to open with side force of up to 30 Pa (kg/m2)
- Must be able to lock automatically on closing
- Must support access port to unlock manually from outside of otherwise sealed box 
- Must only use power when unlocking
- Must be quiet in operation, no more than 20 dB
- Must be not cost more than $25 per lock
- Duty cycle of 20 opens/closes per day
- Must be made from readily available parts (just in time delivery)
- Can be level, edge or PWM triggered with a 5VDC signal
- Power can be supplied separately up to 24VDC
- Must be no more than 100mm x 50mm x 50mm in size
- Latch throw must be at least 10mm
## Tasks

- [x] Order servos ➕ 2025-05-30 ✅ 2025-05-30
- [x] Order springs ➕ 2025-05-30 ✅ 2025-05-30
- [x] Create a circuit to test the latch using PWM pins on the RPi ➕ 2025-05-30 ✅ 2025-06-03
- [x] Test that the servo can open under side pressure ➕ 2025-05-30 ✅ 2025-06-03
- [-] Create `SoftPwm` class and use it to drive the servo ➕ 2025-06-04 ❌ 2025-06-18
- [-] Design a housing for the latch that the servo can attach too ➕ 2025-05-30 ❌ 2025-06-18
## References

- [MG-90S Micro Servo Datasheet](https://www.electronicoscaldas.com/datasheet/MG90S_Tower-Pro.pdf)