I would expect unsuitable design of the detector chamber as most likely reason. Can you show a drawing?
Are you sure that the 10 MOhm resistor can be measured in circuit?
How do you check oscillator operation? Probably difficult with standard 10 MOhm oscilloscope probe.
Hi,
simple test:
measure the supply voltage
* when battery is active
* when battery is not active.
Tell us the values.
Klaus
Hi,
The circuit surely doesn't work, at least not the way you think it works.
Too bad, that you didn't give the requested values.
Issues:
* the resistor values are not suitable. They consume at least 300 times the current of the smoke detector...and all this from the battery.
* the TL081 is not suitable to operate from3V single supply
* the TL081 output voltage range is not suitable to drive the MOSFET correctely
* the TL081 input common mode range is not suitable
* the MOSFET V_gs is not suitable.
What really happens:
* either the diode 1N4148 is conductive...with a huge voltage drop of about 0.5...0.7V
* or the MOSFET internal body diode (not shown) is conductive, with about the same voltage drop
* and there might be a case where the MOSFET is partely conductive..with a resistance mabe in the range of some kiloohms.
Functionally the same could be done if you leave the 1N4148, replace the Mosfet with another 1N4148 and dissmiss all other parts.
Then you are low power and don't need 500 times bigger batteries.
Or simply use a single BAT54C and reduce the voltage drop.
Klaus
Hi,
I don't see any disadvantage of a single BAT54C against your circuit.
Even better - because less voltage drop - use an "ideal diode" circuit..
Klaus
I would expect unsuitable design of the detector chamber as most likely reason. Can you show a drawing?
Can anybody help me please?! What kind of IR LED and photo-diode I should use to work correctly?
It sounds as though the photodiode needs to be adjusted until you find what's known as a 'good operating point.' I believe you need to adjust bias through the photodiode, so that its idle state reaches a point where the slightest change of light level causes a change in its output. You may find you need to apply greater gain as you amplify diode response.
but when I replace IR LED and detector with 3mm ones (like figure below) it doesn't work even when there is not any chamber and emitter-detector are in front of each other! What is the problem!?
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