Augment the PF100 Harman Thermostat.

Can't really help you directly, but I can tell you this..

It will be hard to tap into a circuit that is designed to turn on an LED and use that to turn on another device (like a relay or buzzer). Indicator LEDs use low voltage like you already have seen at around 1-2v. Furthermore the circuit will most likely not handle much more current than the LED draws. The only way you may be able to do this is by adding to the circuit to accomodate a heavier load. Like adding additional transistors or maybe a solid state relay that operates of very low voltage.

Sorry, not much help, but thats probably why no other response since it's not an easy thing to do unless you have a circuit diagram and good knowledge of electronics.

dmaclaren said:

I am thinking about using two in a chain.

Also, I am going to look into some audio unit that I can add to the back of the thermostat so when the light is activated, I can then hear an audio tone.


My guess is I can find something on line or at Radio shack.

Now at the least it will be something small as the power I am sure is very little. At the most, I will need a relay and use the power from the light to trigger the alarm.


Does anyone with experience in this area have input?

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Guess i don't understand exactly what it is you are trying to accomplish here. Please enlighten me. By the way, nice looking install!

As much tinkering and maintenace you will be doing to that furnace. I think you'll never let it get close to running out. Since you have no real time hopper level indication. I bet you check on it once a day.

Instead of messing with the electronics of the stove/furnace I would rig up something completely independent if you wanted an audible alert to low pellets.

Maybe get a SPST normally-closed momentary switch and attach an aluminum plate on a hinge that depresses the button on the switch when there are pellets on top of it. When there aren't enough pellets it will release the switch, close the circuit and activare whatever you have it hooked up to.

http://www.radioshack.com/product/index.jsp?productId=2062540&filterName=Type&filterValue=SPST
http://www.radioshack.com/product/index.jsp?productId=2062399

Use a 9v battery, a car battery or get a door bell transformer and plug it in.

If your technically minded, another easy way would be to use an optical sensor with an LED shining across your hopper. When the optical sensor sees the LED it will indicate a low fuel situation that could operate a relay. You'll need to build a small proto board to power the whole thing.

http://www.vishay.com/optical-sensors/list/product-83774/

I love tinkering with little things like this

I was thinking about something like that but didn't know how the dust would affect it....

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_32602_-1

Min: 1.0vDC

The PF100 holds 4 bags in the hopper.......I would think that it would be easier if the need be, to just attach
another hopper!!
On the coldest days below zero, I will not use 4 bags, and I am heating a large house.

dmaclaren said:

I believe it's VAC on the low voltage.

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Rectifier?