Here is an update on an old topic...
I have an Onkyo TX-NR708 and I need to monitor power status to turn on my SubWoofer AMP and raise my center channel speaker. I used to use this current sensor http://www.phenixcontrols.com/Current_Sensor/9993/, but when I turned on the Ethernet based automation interface, the Onkyo's power usage became unreliable.
Plan Z (all the easier plans exhausted - I couldn't even find a video output monitor) became monitoring the status of the StandBy light on the front panel.
This tiny little light goes on when the stereo is off, so I also had to invert the status.
The heart of the project is my favorite amplified relay: http://www.elkproducts.com/product-catalog/elk-924-sensitive-relay
After a little reverse engineering I have the schematic:
Next step is finding a photo transistor sensitive enough to pick up the light from the tiny standby led.
www.mouser.com/ds/2/311/pt80a_Pb_free_2008_08_14-37737.pdf
The LPT 80 A turned out to be perfect. First it is sensitive to visible light (most of the phototransistors I found are IR only), and second, the transparent case makes it easy to position over the LED.
While the LPT 80 A was able to turn on/off with the StandBy LED, the transistor wasn't closing enough to control my sensitive relay. To solve this, I added a 2N3904 in a common collector darlington arrangement to amplify the signal. I literally soldered the 2N3904 to the LPT 80 A so the signal across the wires is strong enough for decent noise immunity.
Be sure to use enough black electrical tape to prevent stray light from activating the sensor.
To get the reverse effect, I used a 47K resistor to hold T- low and used the phototransistor darlington to pull T- up. Thus when the sensor sees light, it raises T- and keeps the relay off. When the stereo is on and the standby LED is off, the sensor turns off and allows the 47K resistor to trigger the relay.
--Bob
I have an Onkyo TX-NR708 and I need to monitor power status to turn on my SubWoofer AMP and raise my center channel speaker. I used to use this current sensor http://www.phenixcontrols.com/Current_Sensor/9993/, but when I turned on the Ethernet based automation interface, the Onkyo's power usage became unreliable.
Plan Z (all the easier plans exhausted - I couldn't even find a video output monitor) became monitoring the status of the StandBy light on the front panel.
This tiny little light goes on when the stereo is off, so I also had to invert the status.
The heart of the project is my favorite amplified relay: http://www.elkproducts.com/product-catalog/elk-924-sensitive-relay
After a little reverse engineering I have the schematic:
Next step is finding a photo transistor sensitive enough to pick up the light from the tiny standby led.
www.mouser.com/ds/2/311/pt80a_Pb_free_2008_08_14-37737.pdf
The LPT 80 A turned out to be perfect. First it is sensitive to visible light (most of the phototransistors I found are IR only), and second, the transparent case makes it easy to position over the LED.
While the LPT 80 A was able to turn on/off with the StandBy LED, the transistor wasn't closing enough to control my sensitive relay. To solve this, I added a 2N3904 in a common collector darlington arrangement to amplify the signal. I literally soldered the 2N3904 to the LPT 80 A so the signal across the wires is strong enough for decent noise immunity.
Be sure to use enough black electrical tape to prevent stray light from activating the sensor.
To get the reverse effect, I used a 47K resistor to hold T- low and used the phototransistor darlington to pull T- up. Thus when the sensor sees light, it raises T- and keeps the relay off. When the stereo is on and the standby LED is off, the sensor turns off and allows the 47K resistor to trigger the relay.
--Bob