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Topic: Need Help Verifying the Circuit (Read 510 times) previous topic - next topic

Anirudh_Ram

This is the new one. Discard any previous ones.

srnet

The only way I would expect to make sense of that schematic would be to re-draw it with pencil and paper into a logical layout.   
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Smajdalf

Pleas insert the images so we don't have to download them:

The transistors have collector and emitter switched. Bipolar transistors work reversed but with much worse characteristics.
You have the base resistors R1 and R2 at wrong location. They should be between the base of the transistor and what is driving it (i.e. R2 should be between base of T2 and pin D8).
In this particular configuration you can use single resistor between GND and emitter of T2 instead of R1 and R2. Something like 220 Ohm should be "reasonable" value for the resistor.
The connection between 5V and S1 including D4 does nothing. It can be probably safely removed.
When S1 is pressed D7 pin is connected to the unregulated battery voltage. It will die unless protected somehow. Large (about 100k) resistor should be enough to protect the pin and it will work as intended (unless you rebuild the circuit to very low power).
It is common to "name" transistors Q (Q1, Q2, ...), not T. I have no idea why.
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

Anirudh_Ram

So are you saying I am supposed to flip both transistors?

And Diode D4 is there to resist the unregulated voltage from 9v or 7.2v. This prevents the 5v Arduino pin from dying. Isn't this diode needed there then?

Smajdalf

Why do you think Vcc should be connected to the S1 switch? I think the whole connection is pointless. So you should remove both the diode D4 AND connection between Vcc and S1.

Depending on forward voltage drop of diodes and batteries used and Arduino's linear regulator dropout voltage it is possible the supply voltage of Arduino will be less than 5V - it is nearly sure when powered from the backup battery via S1 and D3. I guess it will be more than Arduino's BOD voltage but it may cause problems. You should try it on a breadboard.
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

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