Custom 3-PIR GSM Anti-Theft Security Alarm with SMS, Call & Relay

Custom 3-PIR GSM Anti-Theft Security Alarm with SMS, Call & Relay

PROJECT DESCRIPTION:

I am looking for an experienced embedded hardware and firmware developer to design and develop a custom human motion / anti-theft security alarm using an ATmega328P (Arduino-compatible) microcontroller.

The device will use 3 external PIR motion sensors connected to the main PCB through long cables. The main feature is a selectable PIR detection threshold of 1, 2, or 3 sensors. This will help reduce false alarms.

MAIN PIR LOGIC:

The device has:

* PIR 1
* PIR 2
* PIR 3

The user can select the required number of PIR sensors that must detect movement.

Threshold 1:
Any one PIR becomes active = intrusion confirmed.

Threshold 2:
Any two PIRs become active = intrusion confirmed.
PIR1+PIR2, PIR1+PIR3, PIR2+PIR3 or all 3 should trigger.
Only one PIR should NOT trigger.

Threshold 3:
All 3 PIRs must become active = intrusion confirmed.

The threshold should preferably be selected using a physical 1/2/3 selector, such as a rotary switch or suitable DIP/selector switch.

When an intrusion is confirmed:

1. Trigger relay output
2. Send SMS
3. Make phone call
4. Show status through LEDs

PIR SENSOR CONNECTION:

All 3 PIR sensors will be external and connected to the main PCB through separate connectors.

The PIRs will use long cables because they may be installed at different locations.

The PCB/firmware should consider:

* Long cable operation
* Electrical noise
* Signal interference
* Proper grounding
* Input protection/filtering
* Reliable HIGH/LOW detection
* Suitable connectors

Please recommend the suitable connector and practical maximum cable length.

GSM:

The device must support:

* SMS
* Voice calling
* SIM card
* Approximately 4–5 emergency phone numbers

Please recommend the best currently available GSM/cellular module for this project based on:

* SMS reliability
* Voice call support
* Network availability
* Power consumption
* Current peaks
* Long-term product suitability
* Availability and cost
* Bangladesh network compatibility

Do not automatically assume SIM800L is the best option. Please recommend the appropriate module for a new commercial product.

The GSM power supply must be properly designed because GSM modules can have high current peaks during transmission and calls.

SMS:

When an intrusion is confirmed, send an alert SMS to the configured phone numbers.

Example:
"ALERT! Motion detected. Please check the location."

Approximately 4–5 phone numbers should be supported.

Phone numbers must be stored in non-volatile memory (EEPROM or equivalent) and remain saved after power loss.

Please recommend the easiest customer configuration method, such as SMS commands, PC configuration, or another practical method.

PHONE CALL:

After a confirmed intrusion, the device should automatically call the configured emergency numbers.

Please implement sensible call logic with timeout/retry control so the device does not continuously call all numbers.

The exact call sequence can be finalized during development.

SMS/CALL ON/OFF:

There will be a dedicated physical SMS/Call ON/OFF switch/button.

When OFF:

* PIR detection continues
* Relay can continue working
* No SMS is sent
* No phone call is made

When ON:

* SMS and calls operate normally

RELAY:

One relay output is required for an external device such as:

* Siren
* Alarm
* Light
* Other security equipment

Use proper relay driver and protection circuitry.

STATUS LEDs:

Provide clear status LEDs for:

* PIR detection/status
* GSM/network/SMS/call status
* Alert/communication status

Exact LED behavior can be finalized with the developer.

MICROCONTROLLER:

Preferred MCU:
Microchip/Atmel ATmega328P.

I prefer the ATmega328P to be directly integrated into the custom PCB rather than using a complete Arduino Uno board.

Firmware should be Arduino-compatible C/C++ and fully provided with source code.

BATTERY:

Power source:
3 × 18650 rechargeable Li-ion batteries.

The battery holders will be mounted directly on the main PCB.

The PCB must include:

* Battery connection/holders
* Battery charging circuit
* Battery protection
* Buck converter/regulator
* Proper power distribution

Please recommend the best battery configuration and power architecture.

CHARGING:

Integrated charging circuit with external charging port.

The design should include appropriate:

* Li-ion charging
* Overcharge protection
* Over-discharge protection
* Short-circuit protection where appropriate
* Charging indication if practical

POWER MANAGEMENT:

Proper regulators/buck converters must be selected for the ATmega328P, PIR sensors, GSM module and relay.

The GSM supply is especially important. The circuit must handle GSM transmission/call current peaks without causing voltage drops, GSM resets or ATmega resets.

Use appropriate bulk and decoupling capacitors and proper PCB power/ground design.

POWER SWITCH:

Include a physical main ON/OFF switch for the device.

SIM:

Include a suitable SIM card holder that is reasonably accessible.

PROGRAMMING:

Provide a programming/debug connector so the ATmega328P firmware can be updated without removing the MCU.

Please provide programming and firmware update instructions.

FIRMWARE:

Firmware should include:

* 3 PIR monitoring
* 1/2/3 threshold selection
* PIR confirmation/timing
* Relay control
* SMS
* Phone calling
* 4–5 phone number storage
* EEPROM storage
* GSM timeout/recovery
* Network reconnect where possible
* Watchdog timer
* Protection against repeated SMS/calls
* Safe startup/restart behavior

The system should avoid sending repeated alerts continuously from one long PIR activation. A suitable cooldown/alarm state should be implemented.

PCB DESIGN:

Create a complete custom PCB containing:

* ATmega328P
* GSM module
* SIM holder
* 3 PIR connectors
* Relay and driver
* Status LEDs
* 3 × 18650 battery holders
* Charging circuit
* Buck/regulator
* Main ON/OFF switch
* SMS/Call ON/OFF switch
* 1/2/3 PIR threshold selector
* Charging connector
* Programming connector
* Required protection components

PCB design should consider GSM RF/antenna placement, high-current paths, battery current, relay noise, grounding, decoupling and long PIR cables.

The PCB should be suitable for future commercial production and fit inside a practical enclosure.

TESTING:

The complete system must be tested.

PIR tests:

* PIR1 only
* PIR2 only
* PIR3 only
* PIR1+PIR2
* PIR1+PIR3
* PIR2+PIR3
* All 3 PIRs

Test every threshold setting.

Also test:

* SMS
* Phone calls
* Multiple numbers
* GSM network loss/recovery
* Battery operation
* Charging
* GSM current peaks
* Relay operation
* Long PIR cables
* Power restart/recovery

DELIVERABLES:

Hardware:

1. Complete schematic
2. PCB source/design files
3. Gerber files
4. BOM
5. PCB dimensions
6. Component specifications
7. Connector/pinout documentation

Firmware:

1. Complete ATmega328P source code
2. Compiled HEX/firmware
3. EEPROM configuration
4. Programming instructions
5. GSM configuration details

Documentation:

1. Circuit explanation
2. Pin configuration
3. PIR wiring diagram
4. Battery/charging information
5. GSM setup
6. Phone number configuration
7. Threshold selection instructions
8. Relay connection information
9. Testing report

All source code and original hardware design files must be delivered. I do not want only compiled firmware or screenshots.

FREELANCER REQUIREMENTS:

Please apply if you have experience with:

* ATmega328P / Arduino
* GSM modules
* SMS and voice calling
* PIR sensors
* 18650 Li-ion battery systems
* Battery charging
* Buck converters
* Custom PCB design
* Embedded C/C++
* EEPROM
* Relay control

Experience developing GSM security alarms, anti-theft devices or similar commercial electronics products is preferred.

PLEASE ANSWER THESE QUESTIONS IN YOUR PROPOSAL:

1. Which GSM module do you recommend and why?
2. Does it support SMS and voice calls?
3. How will you handle GSM current peaks?
4. What battery configuration do you recommend for 3×18650?
5. What charging/protection circuit do you recommend?
6. How will you handle long PIR cables?
7. How will you store 4–5 phone numbers?
8. How will you prevent repeated SMS/calls from continuous movement?
9. Have you developed a similar GSM security device before?
10. Which PCB design software will you use?
11. Can you provide complete source code and PCB source files?
12. Can you build and test a physical prototype?

FINAL PRODUCT GOAL:

This is intended to become a real commercial security product, not just an Arduino demonstration.

The final system should be reliable, stable, compact, low-power, easy to configure, easy to manufacture and resistant to false alarms.

Basic operation:

3 PIR Sensors → Select 1/2/3 Detection Threshold → Confirm Human/Intrusion → Relay → SMS → Phone Call