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Sameer Graded

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Abhijit Kshirsagar Kshirsagar 2022-04-26 14:11:17 +05:30
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1. Your scans are very poor quality and hard to read.
2. Correctly identified that reliability is so important that price of unit is not important.
3. Why did you not consider adding some kind of remote signalling? What if the attending person is far away and does not hear the buzzer? Some SMS / wireless based alert would have been good. Also, what about a graded approach - e.g. Alert Level 1 when humidity is 5% outside range, alert level 2 when 10%, etc...
4. File #2 should have had the blok diagram. You have drawn a mix of circuit and block diagram - even within the power supply for example:
/*
┌───────────┐ ┌────────────┐
│ transf. │ │Linear │
───────►│ rectifier ├─────►│regulator ├────┐
│ filter │ │7805 │ ▼
│ │ │ │ 5V Regulated
└───────────┘ └────────────┘ VCC
┌─────────┐ ┌────────┐ ┌───────────┐ ┌─────────┐
│ │ │ Signal │ │Comparator │ │ LEDs │
│Sensor ├────► Cond. ├──►│ ├───►│ │
│ │ │ │ │ │ │ │
└─────────┘ └────────┘ └───────────┘ └─────────┘
*/
5. Design notes:
Opamps cannot driver LEDs and buzzers directly - you need some buffering / current boost - maybe a transistor stage.
What kind of components should be chosen? precision resistors, some trimpots / variable Rs to calibrate in the field right?
Buzzer will be loud enough when mounted in the same "box"? Why not mount it externally?
6. Power supply efficiency is poor, which means heat will have to be dissipated. Where is the heat sink / thermal management?
If the power supply does fail, how does it alert the user? There is no power "on" LED to show that the device is awake.
7. Industrial Design:
The environment is humid - what is the plan for keeping the inside of the box free from condensation?
8. KICAD Design
Schematic: Why choose OPA op amp instead of something more generic like LM328 or LM741 or perhaps OP07? The LM2904 is just Rs4 per piece - this op amp is ~Rs300.
LEDs are connected wrongly - they are both in parallel with the buzzer.
No decoupling caps for the pwer supply?
What is the buzzer current? Won't it sag the power rails?
Layout: is not compact, could have planned a little better. Also, buzzer and LEDs could have been closer. How do you plan to label the LEDs? Someone walks up
to the unit whn it is buzzing - how do they know what is the problem? Some kind of labelling should have been mentioned on silk screen or on outer cover.
If the buzzer is inside the water-tight housing, will enough sound come out?
9. BOM and Pricing:
Unit pricing seems a little high, but that is ok.
Have you accounted for shipping handling, import duty etc?
what about cost of assembly - manpower, solder, housing, materials for housing, etc?
You said power supply is external, but you have only counted the parts cost.