Minos Park

writing | projects | photos | drawings | code | lists | cs184 | ocf

Adapting Legacy Callbox System for a 'Smart Home'

This is a draft post.

December 2020

This is slightly different from my previous project (a few years back) where I wired up a simple relay circuit to open the front gate remotely.

I have a callbox that calls a registered number for an authentication whether to let someone into the building or not. The authentication flow is simple – the callbox makes the call and waits for a specific DTMF tone on the line, and if it’s received hangs up and sends the ‘open’ signal to the door.

This is a convenient feature, it works for deliveries, and it works for the times I don’t have keys on me, but instead have my phone. Sometimes though, I don’t have my phone on me either – you see where this is going.

TL;DR: I built a wrapper around this legacy callbox system that allows me to define the authentication flow in software.


  1. Given the problem, identify solutions
  2. Evaluation
  3. Implementation
  4. Test

Tags: draft