Convert Wireless PIR sensor to use power supply instead of Batteries

[Naynesh]

I want to convert a wireless PIR\Door Sensor so that it runs from a power supply rather then battery's

Currently it take a single or double AA 1.5v Battery

I have multiple PIR's so need some kind of a solution where 1 can use one power supply for all the devices.

Specs are below, Any Advice?

Door Contact
Power supply: DC 1.5V (1 x AA 1.5V LR6 Battery)
Satatic current : ≤30uA
Alarm current : ≤40mA

PIR Sensor
Power supply: 1.5V AA battery x 2
Static current: =< 70uA
Alarm current =< 7mA

 

[KrisBlueNZ]

Hi Naynesh and welcome to Electronics Point

You need two voltage regulators. Your best option is a member of the LM317 family. These are three-terminal devices that will drop a DC supply voltage (e.g. 6V from a "wall wart" adapter) down to the voltages you need. The output voltage is set by two resistors.

The standard LM317 is rated for 1.5A output current, which is much more than you need. There are versions of the LM317 in smaller packages with lower current ratings, but the standard version is much easier to find, and the cheaper ones aren't much cheaper, so you might as well use the standard version. The part number is LM317T (or LM317P) (there may be other letters before or after the 'T' or 'P') and it's manufactured by Fairchild, ON Semiconductor, Texas Instruments, and STMicroelectronics. Should be available from any store that sells electronic components, and is available from many web sites.

As well as two resistors to set the output voltage, you need two capacitors; one from the input to the 0V rail, and one from the output to the 0V rail.

Here's the connection diagram from the Texas Instruments data sheet (http://www.ti.com/lit/ds/symlink/lm117.pdf):


You calculate the values for R1 and R2 according to the output voltages you want, using formulas in the data sheet.

 

[Naynesh]

Thanks Kris

I was thinking of getting something like this:
http://www.ebay.co.uk/itm/5pcs-LM25..._Measurement_Equipment_ET&hash=item20e0c81282

Would this be ok to use if i have low voltage input

 

[KrisBlueNZ]

Yes they should be fine. Much more than you need, but you won't need to do any soldering. You'll need an input voltage at least 2V higher than the output voltage. I would use a 6V "wall wart".

 

[Naynesh]

Thanks Kris
I am thinking of buying 7 step down modules to power my devices

To supply power to the 7 modules can I use one of these:
http://www.ebay.co.uk/itm/DC-Power-...ctronics_PowerAdaptors_SM&hash=item35d6e1b29b

Then I will be able to connect all 7 devices using one power supply?

 

[KrisBlueNZ]

Yes, that looks suitable. 12V at 5A is HEAPS to supply seven devices. At that price, that power supply is probably a cheap Chinese POS that could blow up at any moment, so I hope this is not a critical application. Good luck!