Re: Smoke detector circuit with A5303
I think its principle of operation is so that when there is no smoke no light reaches from transmitter to the detector and there is no output, but when there is smoke in the chamber, light from transmitter reflects to the detector and it detects presence of smoke.My problem is that when I put transmitter exactly in front of detector (3mm transmitter-detector) it gives no output!but with 5mm transmitter-detector it works as expected.
Hi,
* let′s assume the circuit of the datasheet works properly.
* Now your circuit doesn′t work...
--> My conclusion: There is a difference between datasheet circuit and your circuit.
If you want to find the difference we need both circuits.
We have the datasheet... but we don′t have any information about your circuit.
--> show us your schematic. With all the informations like voltages, exact part names (especially the used IR devices), values, etc.
Klaus
My schematic is exactly same as datasheet like figure below ,except that I placed a 560kOhm resistor instead of 560Ohm that is connected to the C2 pin, and also I didn't place R1 and R2 because I doesn't need Hush mode and Hush pin is connected to ground.
Hi,
This is what every user says.....
Imagine: If your car doesn′t work...do you give the car′s operating manual to the car repair shop to tell the mechanic how it should work, but leave the car at home?
****
My I ask why? It limits the current to 1/1000 of the initial current.
If your boss says you get 1000 (Dollar, Euro, or any other currency) for the job... are you satisfied if he gives you just 1?
But maybe you have a good reason to thoose 560k ... then you should tell us.
Klaus
How much distance does the light-scattering need to become detectable? I don't think it will work properly if you put them very close together. I think you ought to provide space for a cloud of smoke to form between source and detector. The smoke is thin, barely visible.
Adjust the aim of the source so that clear air just barely creates a reading from the detector. The goal is to adjust things so that the slightest presence of smoke causes the reading to go up.
I see the problem that the A5303 input circuit operation isn't even remotely explained in the datasheet. According to the scarce description, the gain is set by capacitors rather than resistors. The purpose of the 560 ohm series resistor isn't mentioned, why did you place 560k?
It's surprising at first sight that a photo diode is bypassed with a relative low resistor value, but the circuit operates dynamically, so I presume it's required.
Without a detailed design guide for the input circuit, you have to start from the suggested application circuit, take care that the IR-LED and photodiode are corresponding to the specification and the chamber has the expected optical characteristic. You didn't tell about the used LED and photo diode type (beyond showing photos), are you even sure that the "detector" is a photodiode and connected correctly?
I guess that A5303 is mainly applied by smoke detector manufacturers with additional FAE support. Did you ask at Allegro if they can provide supporting documents?
Yes, unfortunately the circuit operation is not explained good. The resistor that is parallel with photodiode have high value not low. I used two kind of tranmitter-detector that are shown below. First with 3mm transmitter-detector and second with 5mm ones. I am not sure about the front part of photodiode in the second figure, I assumed front end is curve-shape end. Is that right?!
It's right at least for Osram SFH 205H photo diode. But it's easy to check photo diodes with a DMM and a light source.