Our gas furnace intermittently fails to ignite, resulting in us waking up to a very cold house here in the frozen tundra.
A Status LED mounted on the furnace control board indicates the status of the furnace as follows:
When a fault is detected, the LED flashes a two digit number code. The first digit is determined by the number of short (about ½ second) flashes and the second digit by the number of long (about 1 second) flashes. For example, three short flashes followed by four long flashes is code #34.
Unfortunately, unless one happens to be looking at the LED (an unlikely event), there is no alarm to indicate that a fault exists other than waking up (or coming home) to an alarmingly cold house.
At this time, in order to be alerted to the flashing LED, I have aimed a webcam camera at the LED and set it up for motion detection. I wrote a Visual Basic program to monitor the webcam and when motion (LED flash) is detected, a computer: 1) sounds an alarm; 2) sends me an email message; 3) sends a text message to my cell phone.
This system works OK; however, I would like to replace the webcam with a circuit somewhat similar the one discussed here: http://forum.allaboutcircuits.com/showthread.php?t=18501&highlight=%22furnace+led%22.
Just as iONic’s picture shows (http://forum.allaboutcircuits.com/attachment.php?attachmentid=6843&d=1233100178 ), I want to fit an appropriate optical device (phototransistor?)in heat-shrink tubing over the control board LED and bring the leads out into a small circuit box.
Also leading into the circuit box would be two wires from the computer’s DB9 serial port. One wire is connected to Pin7 of the serial port and the other wire is connected to Pin8.
The computer program sets Pin7 high to provide approximately +12vdc to the furnace alarm circuit. The program then repeatedly polls Pin8. As long as the electronic switch remains open, Pin8 is low and all is well. If the switch closes, Pin8 goes high and an alarm event fires.
Pin7 + >----
.........../ electronic switch
Pin8 <-----
As I understand it, in this circuit when the R1 sensitivity control is adjusted appropriately and the light falling on Q1 flashes, Q2 will conduct and Pin8 will go high.
I would appreciate it if someone would suggest how to modify (or replace entirely) this circuit so that it would work in the scenario I’ve described. Ideally the circuit would latch Pin8 high when flashes are detected.
Obviously I’m a newbie, so ANY help will be greatly appreciated.
Thanks.
A Status LED mounted on the furnace control board indicates the status of the furnace as follows:
- LED on continuously (steady glow): All systems are functioning normally
- LED flashes on/off: A fault is preventing the furnace from starting
When a fault is detected, the LED flashes a two digit number code. The first digit is determined by the number of short (about ½ second) flashes and the second digit by the number of long (about 1 second) flashes. For example, three short flashes followed by four long flashes is code #34.
Unfortunately, unless one happens to be looking at the LED (an unlikely event), there is no alarm to indicate that a fault exists other than waking up (or coming home) to an alarmingly cold house.
At this time, in order to be alerted to the flashing LED, I have aimed a webcam camera at the LED and set it up for motion detection. I wrote a Visual Basic program to monitor the webcam and when motion (LED flash) is detected, a computer: 1) sounds an alarm; 2) sends me an email message; 3) sends a text message to my cell phone.
This system works OK; however, I would like to replace the webcam with a circuit somewhat similar the one discussed here: http://forum.allaboutcircuits.com/showthread.php?t=18501&highlight=%22furnace+led%22.
Just as iONic’s picture shows (http://forum.allaboutcircuits.com/attachment.php?attachmentid=6843&d=1233100178 ), I want to fit an appropriate optical device (phototransistor?)in heat-shrink tubing over the control board LED and bring the leads out into a small circuit box.
Also leading into the circuit box would be two wires from the computer’s DB9 serial port. One wire is connected to Pin7 of the serial port and the other wire is connected to Pin8.
The computer program sets Pin7 high to provide approximately +12vdc to the furnace alarm circuit. The program then repeatedly polls Pin8. As long as the electronic switch remains open, Pin8 is low and all is well. If the switch closes, Pin8 goes high and an alarm event fires.
Pin7 + >----
.........../ electronic switch
Pin8 <-----
As I understand it, in this circuit when the R1 sensitivity control is adjusted appropriately and the light falling on Q1 flashes, Q2 will conduct and Pin8 will go high.
I would appreciate it if someone would suggest how to modify (or replace entirely) this circuit so that it would work in the scenario I’ve described. Ideally the circuit would latch Pin8 high when flashes are detected.
Obviously I’m a newbie, so ANY help will be greatly appreciated.
Thanks.
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