12 Volt DC PIRs for Outdoor Use

I've wanted to automate the operation of some external lights in my home for a long time, and PIR motion sensors are a must. I already have several as part of an intruder alarm system, but they are not rated for outdoor use; electronics that is typically uses components with wider than normal operating temperatures (e.g. -40 to +85 degrees Celsius instead of 0 to +70), and conformal coating is often used to protect circuitry from moisture (condensation).

When I first looked for external PIRs (several years ago), I found that almost every one of them was designed to be powered by the mains, and to switch a mains load (a lamp). But I need to drive the inputs of a microprocessor based control system from the PIR, so I would prefer a contact closure (volt free) output. I did find one or two low voltage DC units, but they were horrendously expensive (nearly 100 GBP).

A more recent search turned up a much more reasonable solution:

12V DC Outdoor PIR Motion Sensor

This unit retails for under 25 GBP from Solar and Wind Power Systems. It is IP44 rated, runs from a 12 Volt (AC or DC) power supply and has a relay that can switch up to 10 Amps. It allows adjustments to on-time, range (sensitivity) and ambient light.

Note that the unit is supplied with a 4 way terminal block that is quite large (appropriate for 10 Amps). I swapped this for a smaller one. Also, the knock-outs molded into the ABS plastic housing are quite difficult to remove - I resorted to drilling them out.

Here's a video of a quick test of one. In this setup, the ambient light adjustment is at maximum (to allow daylight operation), the range/sensitivity is low, and the on-time is at a minimum - corresponding to about 5 seconds. The power supply is 12VDC, and the output is wired to ground the cathode of a blue LED - the anode is wired to 12V via a 470R resistor.

Notice that the unit's output remains on while the PIR is detecting motion, and stays on afterwards for 5 seconds.

I checked the range quickly in this setup, and detection worked reliably at 4 meters in daylight.