wuchy143
Member
Hi All,
I"m using photomicrosensors and encoder wheels to sense movement.(Quadrature encoding) My circuit is below. It's in a +5V system with a micro controller which connects up to the USB bus and enumerates as a mouse(trackball).
My problem is when I turn the encoder wheel very fast(turning it on every 2-3ms) the transistor inside the photomicrosensor cannot switch fast enough to reach +5V. Essentially what you see is a signal that goes from a solid 0V up to about 4.0V. Then when I slow down the encoder wheel the signal now transitions a full 0V to +5v.
Intuition told me that if I put a stronger pull up(lower the resistance from 7.5k to 2k) that will fix my turn on and off times. It worked. I'm able to get the full transitions now matter how fast my hand can move the encoder wheels.
Can anyone clear what's going on here for me? I'm unfamiliar with these types of transistors and the datasheet is a little confusing. It appears that it should switch plenty fast enough but it clearly is not....any help?
The topology here is an common emitter. I've tried the common collector and you probably guessed that I have the same problem but now it's not reaching 0v when you move the wheel very fast.....
Thanks all
Datasheet for the part is: https://media.digikey.com/pdf/Data%20Sheets/Omron%20PDFs/EE-SX19x,10xx.pdf
-mike
I"m using photomicrosensors and encoder wheels to sense movement.(Quadrature encoding) My circuit is below. It's in a +5V system with a micro controller which connects up to the USB bus and enumerates as a mouse(trackball).
My problem is when I turn the encoder wheel very fast(turning it on every 2-3ms) the transistor inside the photomicrosensor cannot switch fast enough to reach +5V. Essentially what you see is a signal that goes from a solid 0V up to about 4.0V. Then when I slow down the encoder wheel the signal now transitions a full 0V to +5v.
Intuition told me that if I put a stronger pull up(lower the resistance from 7.5k to 2k) that will fix my turn on and off times. It worked. I'm able to get the full transitions now matter how fast my hand can move the encoder wheels.
Can anyone clear what's going on here for me? I'm unfamiliar with these types of transistors and the datasheet is a little confusing. It appears that it should switch plenty fast enough but it clearly is not....any help?
The topology here is an common emitter. I've tried the common collector and you probably guessed that I have the same problem but now it's not reaching 0v when you move the wheel very fast.....
Thanks all
Datasheet for the part is: https://media.digikey.com/pdf/Data%20Sheets/Omron%20PDFs/EE-SX19x,10xx.pdf
-mike