jiblankman
- May 26, 2013
- 3
- Joined
- May 26, 2013
- Messages
- 3
I am trying to make a circuit to detect a telephone ringing signal and output about a 3V signal. I am new to electronics and have been teaching myself from whatever sources I can find. I have hit a situation that I cannot figure out. Hopefully someone can help me understand what is happening here. Thanks in advance.
I am using the attached circuit which I found at epanorama.net/circuits/telephone_ringer.html"http://www.epanorama.net/circuits/telephone_ringer.html. All parts are as listed, the zener diode is 15V 500 mW. (I tried the other circuit on that page as well.)
The circuit seems to work, but I am confused by some things. The circuit diagram shows that I should be getting an output voltage across the collector/emitter. However, I get no voltage on my meter. When I connect the leads to the base and collector of U1 I get 0.4 volts with no current when the phone rings. Here is the optoisolator that I am using http://www.mouser.com/ds/2/427/4n25-240323.pdf.
I thought I understood how a npn transistor operates, but was confused by this. Since it worked consistently, I was going to go with it anyway.
Next, I tried to amplify the signal to about 3V (2.5-3.3V) is the input range, but cannot get that to work correctly either. I tried using another npn transistor with the positive output of the optoisolator connected to the base, 3V connected to the collector. I tried including a 1K and 10K resistor between the optoisolator and transistor as well. All I get is a constant 2.7V output whether the phone is ringing or not. I tried connecting the optoisolator to the collector instead, but nothing. Any help would be greatly appreciated.
I am using the attached circuit which I found at epanorama.net/circuits/telephone_ringer.html"http://www.epanorama.net/circuits/telephone_ringer.html. All parts are as listed, the zener diode is 15V 500 mW. (I tried the other circuit on that page as well.)
The circuit seems to work, but I am confused by some things. The circuit diagram shows that I should be getting an output voltage across the collector/emitter. However, I get no voltage on my meter. When I connect the leads to the base and collector of U1 I get 0.4 volts with no current when the phone rings. Here is the optoisolator that I am using http://www.mouser.com/ds/2/427/4n25-240323.pdf.
I thought I understood how a npn transistor operates, but was confused by this. Since it worked consistently, I was going to go with it anyway.
Next, I tried to amplify the signal to about 3V (2.5-3.3V) is the input range, but cannot get that to work correctly either. I tried using another npn transistor with the positive output of the optoisolator connected to the base, 3V connected to the collector. I tried including a 1K and 10K resistor between the optoisolator and transistor as well. All I get is a constant 2.7V output whether the phone is ringing or not. I tried connecting the optoisolator to the collector instead, but nothing. Any help would be greatly appreciated.