Wireless Door Sensor Only works on Battery, not with 3v adapter - Page 1
Forum section: electronics / beginners

author: ibaird44
author_rank: Newbie
timestamp: April 26, 2025, 05:20:35 pm
content: Hi there,I have a wireless door sensor that’s powered by 2 aaa batteries - when you change the state of the door the unit has a red light that indicates it has sent the updated status to the hub and it works just fine on battery power but when I physically wire a 3v power adapter directly to the battery terminals it works for about 3 minutes then stops functioning properly - it no longer flashes the red light and the hub doesn't get the state change notification. This will repeat every time I cycle the power - works on battery forever but stops after 3 mins on Adapter. The Adapter reads at 3.4v. When the unit stops automatically sending the state change I can manually hit the refresh button on the unit and it WILL then send the updated door status to the hub but will never automatically send the state change again until I cycle the power. This will repeat every time I do it - Works fine on battery power, stops working after 2/3 minutes using a power adapter.Any ideas?

author: ibaird44
author_rank: Newbie
timestamp: April 26, 2025, 06:10:38 pm
content: Thanks for the idea, I have already played around with voltages. The unit will work all the way down to 2.7v off an adapter but will still stop functioning properly after 2-3 minutes.

author: ibaird44
author_rank: Newbie
timestamp: April 26, 2025, 06:39:01 pm
content: I do not own a scope, I have a pretty basic setup with a multi tester only.I’m not sure how to differentiate between adapter types - it’s a 3v adapter with a 1amp maximum output.

author: ibaird44
author_rank: Newbie
timestamp: April 26, 2025, 08:03:12 pm
content: I've now tried using a single 3.7 rechargeable battery and the sensor behaves as it should - there is something about the adapter power supply that sends some sort of interference into the unit that causes it to stop sending updates - but doesn't shut down the sensor as it will still send the update if manually requested with the Botton on the unit.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 26, 2025, 08:40:44 pm
content: So your switching power supply causes interference. It's hard to find a linear power supply these days. So perhaps you can build one. I don't think you need to regulate the voltage. Just a step down transformer, a rectifier bridge and a large capacitor.

author: MarkF
author_rank: Super Contributor
timestamp: April 26, 2025, 09:15:07 pm
content: You might try adding a bypass/decoupling capacitor on the power inputs of your sensor.I've had rf modules that needed extra capacitance to work. Try something in the range of 10uF.

author: ibaird44
author_rank: Newbie
timestamp: April 26, 2025, 09:22:21 pm
content: If I build something simple like this to step down another DC voltage from a more powerful adapter will it smooth out the interface or do I have to start with a clean 120v AC?https://www.instructables.com/The-Simplest-Cheapest-33V-Supply-in-the-Universe/thanks,iB

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2025, 12:12:22 pm
content: I think you can try to use your existing power supply with a relatively large capacitor like 1000 MicroFarad or more.