Safer Alarm – 7400 competition entry

There are several situations where common alarm systems fail to provide any indication that something bad has happened, such as the limited time sirens can sound. This varies according to your local/country regulations, and but when you return, the siren will most likely be off.

Alarm strobes, if fitted are highly visible deterrents, but:

  • generally provide no external fail safe indication
  • no indication if power totally fails
  • relatively heavy power use, so require a significant battery

Alarm strobe lights can run from battery and be left on for long time, but if the the power has been cut off, will your alarm survive without power during your annual holidays?

This system provides a simple, effective and practical enhancement to existing alarm systems to tell you if your alarm has been triggered, tampered with, or lost power. It has been designed to minimise risks by:

  • giving a safe to enter signal (Green led ONLY)
  • has fail sale indication (NO indicator = issue)
  • indicates if alarm system has been tripped (Red led)
  • indicates if the alarm system has totally lost power (Yellow LED)
  • can survive on it’s own power for 2+ months

The schematic is shown below, and the Eagle version is here.

Safer Alarm -  schematic
Safer Alarm - schematic

Informal testing has shown this circuit works well. It also survived 7+ weeks without power and around fifteen to twenty tests of the indicators.

Safer alarm
Safer alarm

Further testing using an Arduino and LiveGraph software shows a ‘pretty’ graph of the charging of the super capacitor. I also wrote lots of test code to capture the discharge cycle and occasionally turn on the LEDs, but this went badly wrong as the Arduino test circuit injected power into the system via the flip flop inputs when it was logging, or drained power from the system when left connected, but switched off.


safer alarm test setup
safer alarm test setupCharging the supercap (LiveGraph)


Charging the supercap (LiveGraph)
Charging the supercap (LiveGraph)



I have just started an open source project to get community help to take this project further. If this project was awarded any prizes,they would be used to encourage further community input to this project (and not given to me or my family, friends, relatives).

Further enhancements could include the use of a pico power AtTiny PIC, this would also open opportunities for more enhancements, including more indicators or count of times alarm triggered, and remote indication, whilst keeping low price and matching input signals to typical alarm active collector active low outputs.

Inspirations from Open Hardware Summit 2011

Here is a selection of presentations that I found really really inspiring from the recent  Open Hardware Summit. I have also included brief notes highlighting the key points that inspired me.

My apologies to those presenters not singled out below – this does not mean your talk was not inspiring! It just means that I focussed on the key content that really inspired me and changed my thinking. It also means that I have only read the static document, and not seen and heard your presentation, which makes a huge difference!

  • Gabriella Levine, Protei: Open Oceans and Open Hardware: Protei, a proliferating fleet of DIY sailboat drones to clean up oil spills
    • Collaborative:People and professionals from all over the world  creating Protei
    • Already talking about reuse “Reappropriated for other purposes”
    • Even though it is very complex involving physical and electronic design, it is not about the tec/hacking, it is about large scale practical use in remote and hostile locations!
    • very well documented – a key to enable others to build and enhance
    • the speed with which the community created, built and deployed

Major use of open source by the scientific community – you want need to follow back to their main sites to see what they are doing – moodular PCI-e cards, major extensions to KiCad, …..


These drove home to me that open source is NOT ONLY about electronics – steam engines to yurts!


Yet another leap in a different direction – I read the title, but it did not really sink about the scale of what we can all be invloved in until I read the presentation.


I would encourage you strongly to read or watch the presentations yourself, as your interests will be different to mine!

You might also want to check out the 2010 summit – it also had some very inspiring talks, and of course keep an eye out here as I have more inpiration posts coming.