forward drop of 1.5V @2A

...means power dissipation of 3W, not that small...

There also exist photo MOSFETs or even SSR gate drivers like VOM1271 (an example, there are ton of similar products, many even in more DIY convenient packages), you take a pair of MOSFETs like IRFZ44 or so, connect Sources together, Gates together, between Gate and Source connect the output of the VOM, the drains then form the power switch. You get about 100mOhm, that means about 0.2V drop, so barely 0.4W total at 2A.

If there is a radio as alarm function, an easiest way will be just to hook a relay (contact rating powerful enough for a halogen) across radio power lines.

In fact, S102/202 optos I mentioned have forward drop of less than 1.5V @2A, so still may be OK even for flashing 12V halogen directly, especially accounting for somewhat constant-current behavior of small power halogen transformers.

To invent an optimized circuit, some hint of actual clock schematics is needed, @lightsofpahrump was asked for, but he prefers to keep silence. Ok, his choice.

You might be able to find a Thomas Duplex Safelight for fairly cheap on eBay. Complete examples sell for a bit but I've found units with missing lamps tend can sell as low as $30-50. They're not a wallpack but they use 35w SOX lamps.

In these things (judging what I have at home) is just one single transformer with one secondary feeding the clock/radio part and then the 12V high current one feeding the halogen. All the switching is then on the low voltage side. So triac would have way too high voltage drop when starting from 12V.

I think the only way to proceed is to trace the buzzer and radio power control circuit and start from there.
To control the radio, there already is some kind of detector/rectifier, as the radio does need a permanent power. And the clock IC very likely provides the same signals all the time (assume one of the clock ICs, not the microcontroller), they are only afterwards blocked by the mode switches.
So depend on how that is arranged, you may either tap on the existing control (if the radio/buzzer switch is after that) or replicate the radio switch circuit to control the relay.

The LM8560 generates only "buzzer" alarm signal by a single PMOS open drain output (it uses PMOS logic technology, so the ground of the clock circuit is positive), so there is a kind of filter circuit which turns that into continuously (when the buzzer is buzzing) available power for the radio.
The is a second "sleep" output, but that works only for the "sleep" function (press the button, it runs the radio for set amount of time and tyen shuts it down), these are combined in the radio power control circuit, but you won't need that (unless you want tye "sleep" function for the lamp asc well). This "sleep" usually goes around the alarm mode switch directly to the radio.

Hi!

I'm located in Illinois in the US.

I have two HPS wall pack fixtures and I love the light from them. However, I've been wanting an example of a LPS fixture but they don't seem available in the US very much. I am interested in a small fixture such as a wall pack with maybe an 18 or 35W lamp and possibly a spare lamp.

Let me know if you have one you'd be willing to sell me!

Thank you.

-Dylan

Well, this all is over-complicated for a person who probably even does not own an oscilloscope.

As a rough hack, I'd try some reasonable sensitive opto-TRIAC like Sharp S102S01 or S202S01 and just connect it's LED input in series with some suitable current-limiting resistor say, 330 Ohms by luck across the buzzer, be it piezo or electromagnetic. If this does not fire, reverse the polarity. TRIAC output could drive high voltage halogen or HF halogen supply directly, I'd be a bit cautious with magnetic 12V transformer, but probably still OK.

I dont think the chip matters that much. I'd do the following :

 - With the buzzer either in circuit or removed (choose how you are going to make it in the end), add a rectifier bridge across it, then few uF capacitor on te DC output. To be nice to the chip which is driving it all (and not short its output with the capacitor which pulls high current to charge), add a few 10's Ohms resistor in series with the input of the rectifier bridge

 - Evaluate what is the voltage in the capacitor. Connect a multimeter across the capacitor, and see how high it charges when the alarm goes off

 - Connect an optoisolator to the capacitor (so the alarm will flash the optocoupler), with suitable resistor for the voltage you measured

 - Connect the other side of the optoisolator to a circuit that will shape the flash seen in the optocoupler to a nice timed pulse. It can be a monostable 555 circuit (look it up, adapt the component values to your needs) or any other circuit which does the same thing

 - Connect the output of the timed pulse to a suitable bipolar transistor or FET and then your relay



I expect that the circuit doesn't apply constant DC across the buzzer when it is silent. (It definitely won't with a magnetic buzzer, but it might or might not if the buzzer is a piezo disc. If there is constant DC there, you may have to add another capacitor (few 10's...100's uF) in series with the rectifier bridge input in order to block the DC

@Ash
The elliptical shape superimposed on a T neck and top is what I traditionally think of with BT. Different sizes based on 1/8" as usual, commonly BT28, BT37, and BT56, but BT15 also exists and was used for some halogens, I am sure you have seen all of these.

That more cylindrical version common to 100/175W MV lamps is usually BT28 size, but I have also seen some rarer BT28s that look more normal, without sharp corners. Looking up "BT28 lamp" yields photos of both types of BT28 envelope. I personally am not huge fan of the less rare more cylindrical version that you are talking about, but it technically is still BT shape.

I have seen those tubular bulbs with only very small bulges with the HQI-BTs, I haven't seen any standard for that size. I haven't seen them referred as "BT##", just plain "BT". Unsure about the specifics there.

BT is a little ambigous as i have seen at least 3 different lamp shapes referred to as "BT" -

 - Elliptical shape, superimposed over T neck and top - Many Iwasaki lamps

 - Cylindrical central section, little bulged, superimposed over T neck and top - Typical US 100/175W Mercury lamps

 - Tubular shape (with rounded top), with one small bulged part in the center - Osram HQI-T and their Chinese clones