I am following along with the Analog Discovery Tutorials: Scope 2: Triggered Acquisition tutorial. I have a very similar but not exact breadboard setup. 4V, 220 resistor, red LED. W1 is setup as the screen below shows, the W1 wire is on one end of the resistor, GND is on the far end of the LED. 1+ is on the same end of the resistor as W1 and 1- is on the other leg of the resistor. 2+ is on the same leg as 1-, and 2- is on the same leg of the LED as GND (hopefully this makes sense, if not, look at the video.) I am using a sign wave but the triangle gives similar results.
I am trying to wrap my head around what I am seeing, am I close
I am feeding the circuit with a sine wave that is 8 volts peak to peak (4V amplitude). It being 8V and not 4V took me a minute to figure out and caused a lot of confusion. The second screen show the scope waveform. Thinking that I was working with 4 volts, it made no sense to me. Once I figured out that I was working with 8 volts, things became a bit more clear. I think that in reality, the two signals needed to be added together (as in the 3rd screen) to get the total drop across the circuit (which should be 8Vpp). The LED only lights when the + voltage is high enough to light it (around 2 volts.) So there is a 2V drop across the resister when the light is on and a 6 volt drop across the LED when the light is off.
When the LED is on, there is very little resistance through the LED which is why I am seeing less than a 8Vpp sign wave on channel 2.
The voltage across the resister is only present when the voltage is above 2 volts (when the LED is allowing current to pass) Otherwise, there is no access to ground which is why the waveform is smaller and for a shorter duration.
Basically, the blue trace is when the light is off and the yellow is when the light is on?
Question
JohnnyG
I am following along with the Analog Discovery Tutorials: Scope 2: Triggered Acquisition tutorial. I have a very similar but not exact breadboard setup. 4V, 220 resistor, red LED. W1 is setup as the screen below shows, the W1 wire is on one end of the resistor, GND is on the far end of the LED. 1+ is on the same end of the resistor as W1 and 1- is on the other leg of the resistor. 2+ is on the same leg as 1-, and 2- is on the same leg of the LED as GND (hopefully this makes sense, if not, look at the video.) I am using a sign wave but the triangle gives similar results.
I am trying to wrap my head around what I am seeing, am I close
I am feeding the circuit with a sine wave that is 8 volts peak to peak (4V amplitude). It being 8V and not 4V took me a minute to figure out and caused a lot of confusion. The second screen show the scope waveform. Thinking that I was working with 4 volts, it made no sense to me. Once I figured out that I was working with 8 volts, things became a bit more clear. I think that in reality, the two signals needed to be added together (as in the 3rd screen) to get the total drop across the circuit (which should be 8Vpp). The LED only lights when the + voltage is high enough to light it (around 2 volts.) So there is a 2V drop across the resister when the light is on and a 6 volt drop across the LED when the light is off.
When the LED is on, there is very little resistance through the LED which is why I am seeing less than a 8Vpp sign wave on channel 2.
The voltage across the resister is only present when the voltage is above 2 volts (when the LED is allowing current to pass) Otherwise, there is no access to ground which is why the waveform is smaller and for a shorter duration.
Basically, the blue trace is when the light is off and the yellow is when the light is on?
Am I missing anything?
Link to comment
Share on other sites
2 answers to this question
Recommended Posts
Archived
This topic is now archived and is closed to further replies.