- #1
quantumnano
- 4
- 0
Hey All,
I am working on developing a current source which utilizes photocouplers (PC817s) on the connection between a digital potentiometer and a PC. I have the photocouplers (not the digital pot yet) so I am trying to verify that the photocouplers are working as expected. The way the circuit is setup, the PC would send data into the ELD side of the coupler and the output would run to the digital pot. I was instructed to hookup a function generator to where the PC would be connected and send a simple square wave through. I am probing with an oscilloscope on the output of the photocoupler. This is my first time working with photosouplers but I was told that the input signal should match the output signal very closely. However, when I put in say a 5V peak-to-peak square wave into the LED side through a series 33K resistor (from the schematic I'm working from), what I read at the output is not a 5V square wave but a square wave more on the order of ~20-30mV. Why is my signal damping so much? Is it my setup or are the photocouplers blown. I thought maybe I was runnign them at too high of a voltage so I used a new one and started at 1V but observed the same results. I don't think there is anything wrong with the devices so am I expecting the wrong behavior. I also tried scaling down the 33kOhm resistor to lower values but even as low as 150 Ohms I am seeing significant damping.
EverythingInvsbl (6:00:46 PM): So I am working on developing a current source which utilizes photocouplers on the connection between a digital potentiometer and a PC. I have the photocouplers (not the digital pot yet) so I am trying to verify that the photocouplers are working as expected. The way the circuit is setup, the PC would send data into the ELD side of the coupler and the output would run to the digital pot. I was instructed to hookup a function generator to where the PC would be connected and send a simple square wave through. I am probing with an oscilloscope on the output of the photocoupler. This is my first time working with photosouplers but I was told that the input signal should match the output signal very closely. However, when I put in say a 5V peak-to-peak square wave into the LED side through a series 33K resistor (from the schematic I'm working from), what I read at the output is not a 5V square wave but a square wave more on the order of ~20-30mV. I ramped to a 10V ptp wave and saw equivalent damping. Why is my signal damping so much? Is it my setup or are the photocouplers blown? I thought maybe I was running them at too high of a voltage so I used a new one and started at 1V but observed the same results. I don't think there is anything wrong with the devices so am I expecting the wrong behavior? I also tried scaling down the 33kOhm resistor to lower values but even as low as 150 Ohms I am seeing significant damping. Any suggestions?
I am working on developing a current source which utilizes photocouplers (PC817s) on the connection between a digital potentiometer and a PC. I have the photocouplers (not the digital pot yet) so I am trying to verify that the photocouplers are working as expected. The way the circuit is setup, the PC would send data into the ELD side of the coupler and the output would run to the digital pot. I was instructed to hookup a function generator to where the PC would be connected and send a simple square wave through. I am probing with an oscilloscope on the output of the photocoupler. This is my first time working with photosouplers but I was told that the input signal should match the output signal very closely. However, when I put in say a 5V peak-to-peak square wave into the LED side through a series 33K resistor (from the schematic I'm working from), what I read at the output is not a 5V square wave but a square wave more on the order of ~20-30mV. Why is my signal damping so much? Is it my setup or are the photocouplers blown. I thought maybe I was runnign them at too high of a voltage so I used a new one and started at 1V but observed the same results. I don't think there is anything wrong with the devices so am I expecting the wrong behavior. I also tried scaling down the 33kOhm resistor to lower values but even as low as 150 Ohms I am seeing significant damping.
EverythingInvsbl (6:00:46 PM): So I am working on developing a current source which utilizes photocouplers on the connection between a digital potentiometer and a PC. I have the photocouplers (not the digital pot yet) so I am trying to verify that the photocouplers are working as expected. The way the circuit is setup, the PC would send data into the ELD side of the coupler and the output would run to the digital pot. I was instructed to hookup a function generator to where the PC would be connected and send a simple square wave through. I am probing with an oscilloscope on the output of the photocoupler. This is my first time working with photosouplers but I was told that the input signal should match the output signal very closely. However, when I put in say a 5V peak-to-peak square wave into the LED side through a series 33K resistor (from the schematic I'm working from), what I read at the output is not a 5V square wave but a square wave more on the order of ~20-30mV. I ramped to a 10V ptp wave and saw equivalent damping. Why is my signal damping so much? Is it my setup or are the photocouplers blown? I thought maybe I was running them at too high of a voltage so I used a new one and started at 1V but observed the same results. I don't think there is anything wrong with the devices so am I expecting the wrong behavior? I also tried scaling down the 33kOhm resistor to lower values but even as low as 150 Ohms I am seeing significant damping. Any suggestions?