Door Stop Alarm issue

[Fergus]

A question for the electronic boys,



I have a couple of these in my man shed but when left switched on their 9V batteries drain within a few days.

So I am experimenting with converting one to use a mains powered 9V supply.

Pics



Sorry about my wiring.





The issue being when switched on it randomly activates without touching the pedal. It can sit there quite happy until I place a finger on but not pressing down the pedal.

OK I understand a little about electrical wiring but electronics is another field.

Is it something to do with 'pure' direct current and pulsating dc. If it is what can I add to correct this issue ?

Any thoughts guys.

This has been helpful but I cannot see what needs to be done, simply and cheaply, to my conversion...or can it.

[trilo]

I'm not too good at these, but I suspect the circuit does not brake when it's idle and it just keeps draining the battery, aka it's constantly "ON"

[inboost]

Fergus, I wonder if the power supply is the culprit. The reason I ask is that we can get DC voltages from an AC source in a number of ways, and the least expensive is by simple rectification. When that mehtod is chosen, you end up with a ripple in the DC supply that perhaps the electronics don't like in that system.

So try this, see if you can find an old 'wall wart' power supply for something that needs clean power like a router, cable modem, phone charger, etc. and wire that in a temporary fashion. The closer to 9v the better but best not much over. I suspect even at 5v the system will work (but perhaps not as loudly?). The higher end wall wart will produce a much cleaner power source than a cheap rectified transformer does.

[Fergus]

Thanks Simon, I have been looking around for another mains unit but it's finding one a) with the correct voltage b) with the correct plug to suit the 5.5 x 2.1 socket I have fitted. I should have ordered a few plugs when I bought the sockets.

I have a Thurlby Bench power supply which I'm sure has a very clean DC output so I will connect it directly to the inner terminals. I can also try varying the voltage as you suggest.

Watch this space.

[Fergus]

Update:

I can confirm the Thurlby dc is smoother than the adaptor so the switch does not fire off until told to.

I don't want to leave it switched on so I need a pure source.

[Fergus]

Yet another update:

My daughter has had one of these (exactly same make/model) for around 3 months and for all that time it has been set to ON. She had not checked it and assumed it would work and upon pressing the pedal it did.



I fitted new batteries to mine so were they duff.

[inboost]

Did you use a Varta brand 9v cell?