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I have used TL084 op amp in infinite gain mode [...]
because Sensor LED generates very small voltage.
my problem is op amp is too sensitive so it reacts when i tough circuit or negative wire (some times evan my fingers reach the circuit [without even touching])this made circuit kind a unstable.other than that circuit works fine.
Could you rephrase the last statement? Sounds impossible to me, either it works fine OR it's unstable I'd say.
unstable mean when I set pot to detect white-black.it works bt sensor senstivity varies time to time so i have to adjust it time to tme
You need to put a filter on it. For example, the light coming from your window will change throughout the day. Basically I think you want to detect a sudden *change* in the signal, not the amplitude, right?For example, a differentiator or integrator op-amp circuit, combined with a comparator IC.
I'm assuming its either/both static electricity or its picking up a slight charge/field about his hand.
Hi,To get a stable output you need to do several things.Sensor must be shielded from ambient light as well as possible, since it will be swamped otherwise and shielding is very easy to do.I'd recommend a modulated signal, as that help reduce ambient influence a lot.To go a step further, a light controlled bias voltage to the sensor will make sure it's operating in its most effective region most of the time.There is no such thing as an IR light detector that won't be affected by the sun, as the sun is rich in IR.Using an IR filter will reduce _some_ artificial light, but since it pass IR and the sun emits IR...
and "a light controlled bias voltage to the sensor will make sure it's operating in its most effective region most of the time." please explain this
what about sensor saturation
about modulating; wont excessive light simply saturate sensors so it wont recognize any kind of signal?
Hi,Big oops!I must have been sleepy - you can't use a TL084 on 5V!Better go for something like a TLC272 or similar.
Hi,Well it wasn't stable, according to yourself and it will never be, even if it was made correctly - try a more suitable op-amp or raise the voltage - or don't, if you think it's working as you want it A different approach, could be using an integrated IR-receiver (of the kind that allows a continuous wave) and adjust the power of the modulated LED to adjust sensitivity. This ought to be much easier for you to get working, but you'll have to go infrared for this to happen, as the integrated receivers are IR.