LDR + LED - Photoresistor

Status
Not open for further replies.
colin mac said:
Sure, slow in electronics terms, but not in human terms but
not perceivable in human terms.
Click to expand...

Not perceivable? - 100's of milliseconds are EASILY perceivable - 500 milliseconds is half a second, I could punch you faster than that!
 
I made a counter with a LDR and laser and uC. No matter how fast I waved my hand back and forth through the laser, no count was missed. That's about 4 counts a second at least.
 
colin mac said:
I made a counter with a LDR and laser and uC. No matter how fast I waved my hand back and forth through the laser, no count was missed. That's about 4 counts a second at least.
Click to expand...

hi Colin,
If you want to measure the 'fastest' rate, switch the laser ON/OFF with a pulse generator. Thats if its not a 'soft start' laser module.

PS: watch out, Nigel is a very fast puncher.

Its all relative anyway.!
 
colin mac said:
I made a counter with a LDR and laser and uC. No matter how fast I waved my hand back and forth through the laser, no count was missed. That's about 4 counts a second at least.
Click to expand...

Four counts a second is 250 milliseconds each, like I keep telling you, this is INCREDIBLY slow in electronics - you're also only switching, you're not doing a linear transfer. If you were talking four MILLION counts per second, that's still not considered fast.
 

We've established that. It's nothing to do with the point I'm making.
LDRs changing resistance is not perceivable.
 
Last edited:
colin mac said:
We've established that. It's nothing to do with the point I'm making.
Click to expand...

So what is the point you're making? - we've all said LDR's are slow devices - you've then seemed to have suggested that they aren't, but quoted an exceptionally slow speed for them (disproving your own point).

What are we missing?.
 
We're arguing whether the reponse time of an LDR is perceivable. You then spun it into an argument of whether LDRs are fast or slow compared to other electronic devices.
 
Last edited:
The speed of components varies quite widely and there are other factors like the current flowing through the cell and the threashold of the comparator, i.e, it takes much longer for the CdS cell to change from 10M to 100R than it does for it to change from 100k to 10k. The response is probably exponential, like a low pass filter.
 
colin mac said:
We're arguing whether the reponse time of an LDR is perceivable. You then spun it into an argument of whether LDRs are fast or slow compared to other electronic devices.
Click to expand...

It's clearly perceivable, or this thread wouldn't be here!

It's slowness is 'usually' an advantage, the "opto-coupler" type device in question is usually used for audio AGC or modulation effects in audio systems. The slow response of the LDR makes it perfect for doing this, and a method using a phototransistor requires special consideration to make it operate at a similar slow speed.
 
Status
Not open for further replies.

Similar threads

J
  • Question
Photoresistor
Replies
8
Views
447
audioguru
A
  • Question
volume attenuator and LDR
Replies
1
Views
708
danadak
A
  • Question
LDR Equivalent from an SMD (phototransistor)
Replies
5
Views
1K
ZipZapOuch
A
  • Question
volume attenuator LDR
2
Replies
30
Views
6K
stereo coffee
S
M
  • Question
Audio activated LEDs
Replies
14
Views
2K
Tony Stewart
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…