Hello Readers,
I am a mechanical engineer but overwhelmed by electronics and motivated to make some. Just a highly energetic beginner.
I have two circuit questions and attached two pics.
1. NPN_2LEDS. - 1 NPN transistor is connected in a simple way in picture. Collector and base is connected to 5v. Emitter is grounded.
The circuit works fine when an LED is connected only to either the emitter or to the collector end.
But when i add another LED (1LED @ emitter and 1 @ collector) , the behaviour is confusing to me.
Only the emitter LED burns while the collector LED is dark and the collector current is zero.
Why is the collector current zero?
2. Arduino with ULN2003 - Pin 13 from the arduino is connected to pin 1 of ULN2003 darlington transistor and its pin 16 connected to an LED.
Circuit works. I am delighted. But when i measure the voltage across pin 1 of darlington transitor and ground the voltage is 1.56V, when the arduino pin supplies 5V. I dont know why.
If i disconnect from the arduino and connect pin 1 of darlington transistor to 5v supply the measured voltage is 4.93 V (and makes sense).
The voltage applied at the other end of the LED is also 5V. Why this difference?
Thanks in advance for your answers.
I am a mechanical engineer but overwhelmed by electronics and motivated to make some. Just a highly energetic beginner.
I have two circuit questions and attached two pics.
1. NPN_2LEDS. - 1 NPN transistor is connected in a simple way in picture. Collector and base is connected to 5v. Emitter is grounded.
The circuit works fine when an LED is connected only to either the emitter or to the collector end.
But when i add another LED (1LED @ emitter and 1 @ collector) , the behaviour is confusing to me.
Only the emitter LED burns while the collector LED is dark and the collector current is zero.
Why is the collector current zero?
2. Arduino with ULN2003 - Pin 13 from the arduino is connected to pin 1 of ULN2003 darlington transistor and its pin 16 connected to an LED.
Circuit works. I am delighted. But when i measure the voltage across pin 1 of darlington transitor and ground the voltage is 1.56V, when the arduino pin supplies 5V. I dont know why.
If i disconnect from the arduino and connect pin 1 of darlington transistor to 5v supply the measured voltage is 4.93 V (and makes sense).
The voltage applied at the other end of the LED is also 5V. Why this difference?
Thanks in advance for your answers.
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