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Daracombe Park Gate Actuator

I have now spoken to the gate repair team, and have established that a hardware/software project to provide a parallel means of actuating the gate is feasible.

This note gives an outline technical design.

How to acutuate the gate

The gate is actuated by closing a pair of contacts on the edge of the controller board inside the intercom box. Currently these contacts just have a connection to the new 5G SIM board. The gate can be actuated by closing these contacts, the simplest way to do this is with a small relay or reed switch.
The new relay would be driven by a board which is connected to Oak House via a cat 5 cable. This board would need:
- Relay to close contacts
- Communications interface (either RS485 or Ethernet)
- Microprocessor to interpret commands
- 12V to either 3.3V or 5V LDO/Buck convertor depending on board chosen
This board would be housed either:
- Inside the current controller box
- In a weatherproof box attached to back of the current control box
Which depends on the size of the board and availble space in the control box.

A suitable board is RTU Modbus 1 Relay board. This board has:
- MODBUS RTU connection running at 9600 baud
- Relay capable of switching up to 10A @ 30V
- VCC 7-24VDC so can be driven either by cable or from the 12V power supply
- Now been ordered from aliexpress
Upgraded power supply - we discusses upgrading the 12V power supply in the control box from 1.5A to 3A, which would give adequate headroom to power an additional board. If a minimal board were to be used then this upgrade may not be necessary.

Cat5 cable to run in a duct along the boundary wall up to the corner with Howton Road (where there is already a box for a solar panel), then along the boundary with Howton Road to the southern back door of Oak House, and then to the server cabinet.. This measures approximately (intentional slight overestimates):

Run	Dimension
Gate to corner of Howton Road	65m
Corner of Howton Road to southern back door of Oak House	20m
Back door of Oak House to server cabiner	10m
Total	95m

I happen to have the remainder of a 100m drun of cat5 cable left from an earlier project which would be suitable.

The cable would naturally be broken with a junction at the corner of Howton Road to fit another connectiono for other purposes.

Outdoors the cable would run in flexible black trunking to protect it.

Handling of cable to server depends on the choice of communications protocol:

Protocol	Server end
RS485	RS485 to uart convertor connected via microcontroller with USB to server. RS485 is currently favoured as this is lower power and known to work over long ranges.
Ethernet	RJ45 termination of ethernet cable, which then plugs directlr into hub

On the server would be a web service which could be connected to via a dedicated subdomain https://gate.oakhousedaracombe.co.uk , this web service would serve a secured web page / app which enabled properties in daracombe park to open the gate. Each device on which the app is installed will be issued with a unique randomly generated key, which will be stored in the device's local memory. The app would require the key to be able to open the gate.. Each time the gate is actuated via the app, it would be checked against the record held on the server. This would ensure that only devices that had been issued with a key would be able to open the gate..

It has been pointed out that a unique code would enable tracking and so could infringe data protection, an alternative which offers the same security as manual keypad entry is for the 4 digit gate code to be stored in the devices local memory. It would be entered by the user whilst installing the app.

Options

Laid out above is system which would provide an alternative means of opening the gate, it would be possible to add further functionality such as a camera at the gate. This would require more bandwidth, and so an ethernet connection. It is worth notinh that the most expensive part of the project (cable to the gate) would remain the same.