Low cost PIR interface

M

MFB

Senior Member
There are often posts asking for advice on interfacing PIR sensor and the following information might therefore be of interest. I recently purchased a ‘Uni-Com’ automatic light unit form Maplin Electronics, which contains a PIR sensor and conditioning circuitry on a removable 4cm x 6cm size board. Unlike most readily available PIR units this one is not mains powered but operates from 5-6 volts. It's LED output can therefore be easily be interfaced to a PICAXE digital input.

The traditional (through hole) circuitry is based on a single low power M7615 PIR controller DIL chip from Mosdesign Semiconductor Corp. It is not necessary to understand this circuitry in order to interface the board but, for the inquisitive, it’s probably based on the example given in the MSC data sheet. One modification that may be needed relates to a LDR that inhibits operation in daylight. If this feature is not required, I suggest removing the LDR and shorting the board’s sensor input to ground.

At this price (about £8) it would be difficult to find a cheaper and more convenient way to interface a PIR to a PICAXE.
 
hippy

hippy

Ex-Staff (retired)
Most household wired burglar alarm PIR's operate from 12V and likely contain a regulator or zener 5V supply which should be possible to remove, along with any on-board reed relay.

Output can either be taken from the relay contacts, relay driver or activity LED. The advantage of using the relay is that the PIR becomes a passive switch to the PICAXE, a direct connection ( via a suitable current limiting resistor if needed ) is equally possible.

Most burglar alarm PIR controller chips don't have LDR inhibitors but it makes sense for that on chips used for exterior lighting systems.

I agree with MFB that a ready-built PIR module is easier than taking a PIR sensor element and building your own circuit. It should be possible to reverse engineer what there is and build it up again on stripboard if that is required.
 
D

Dippy

Moderator
I'll second that. They make life easier.
And they are ideal for general purpose use and as an 'introduction' to detection.

The main advantages, however, of considering 'other' sensors e.g. the NAIS/Panasonic modules are:
1. Size. Some are very small.
2. Power. Some are in the tens/hundreds of microamps.
3. Response time. Not always, but sometimes, the 'burglar alarm' types have unadjustable pulse-count which reduces false triggers and slows down response time.
4. With some modules they provide an analogue output, giving the user more flexibility.

Rolling your own is not for novices really, but gives maximum flexibility.
In fact, in skilled hands, they can be used for direction sensing too.
Horses for Courses as usual eh?

And it goes without saying that all this applies to ALL common sensors e.g. U/sonic and Microwave.
 
D

Dippy

Moderator
Handy chip.
There are a number of similar chips around.

Sadly the operational current is a little high for practical battery powered devices.

These are an option:
http://pewa.panasonic.com/pcsd/product/sens/index.html

I seem to remember some unlensed modules (Seiko?) using <200 uA.

Anyway, lots around. Availability can be a problem, but you pays yer money and takes yer choice.
 
T

Tinhorn

New Member
thanx for teh info on the PIR, I'm always looking for "cheaper-the-better" things like this too. Here in the States, Radio Shack has a $10 PIR module that operates @ <100ua's at 5 volts that I've interfaced to the PixAxe with good results. It's apparently made by this company:

www.parallax.com

I downloaded a 4 page PDF with the spec's from that site (I guess that's where I got it, it's been awhile)

Tinhorn
 
E

eclectic

Moderator
A little more info, for Brits.

I noticed a Philips Spoton sensorlight
in Morrisons today.
£6.84 but BOGOF!
Amazing for £3.42 !
(Including 3 x AAA)

Pic 1 shows a few views.
I removed an LED, then soldered four wires.

V+ (Red) / Batt gnd (black) / Anode (Yel) / Cathode (Grn)
I then measured a few voltages.
Easiest to hack is probably Cathode – ground (green to Black)

Un-triggered / LED's off = ~2.4v

After triggering ~0.027v. Two LED's on for ~20sec.

Range?
No proper tests, but it responded when I waved from ~ 1 metre.

e
 

Attachments

M

MFB

Senior Member
The Philips offering looks like a better deal but I hope you get a range of more than 1 metre. My unit from Maplin operates over a few metres, which might be something to do with it having a much larger lens array than the Philps design. The connections to the board are well labelled and easy to modify. However when the LED drive is disconnected, and used as a PICAXE input, a 10K resistor must be added to ground. This is a bit unusual as most LED drive circuits are open collector and require a resistor to the power line.
 
D

Dippy

Moderator
Thats great value for money ec.

There are a zillion models on the market, but we may have to be a little bit careful in selection.
Sometimes 'cost' needs to be a little lower down on the list of criteria.

Something that switches on for 20 seconds isn't much use for counting people walking past a doorway, so back to horses for courses. And hence, for developers who can afford more than a fiver, the benefits of the specialist modules.

Anyway, on with the list of cheapies....
 
E

eclectic

Moderator
Dippy said:
Thats great value for money ec.

There are a zillion models on the market, but we may have to be a little bit careful in selection.
Sometimes 'cost' needs to be a little lower down on the list of criteria.

Something that switches on for 20 seconds isn't much use for counting people walking past a doorway, so back to horses for courses. And hence, for developers who can afford more than a fiver, the benefits of the specialist modules.

Anyway, on with the list of cheapies....
Click to expand...
Dippy.
My posting was only to inform others.

Buying a working "cheapie" for educational use,
seems a reasonable intention.

Then buy an expensive "real" one.

e
 
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