I have a circuit here that I plan to make a PCB with. The Arduino is supposed to power ON and stay on with the press of Push button 1 (Digital Pin 6 will be updated to high on Press). To Turn off the Arduino you must press push Button 1, while pressing and holding down push button 2 (Delay will be accounted to update D6 to LOW once both buttons have been pushed and released).
The Circuit also contains a 7.2V (Coin-Cell) backup battery along with a primary DC source of 9V coming from the wall outlet (Use of an Adapter Plug).
I am only a beginner to Electronics so please let me know if I am doing things the right way. Also, verify that I have my resistor values right. The Base-Emitter Voltage on the NPN Transistor (2SC945) is 5V. Infact want to make sure all wires leading to the Arduino is 5V to prevent frying the board.
Please suggest any edits I should make in the circuit.
Anirudh_Ram:
How would I put the Arduino to Sleep? Is there a circuit for that?
The way that circuit is drawn makes it very difficult, for someone who does not know your circuit to read. Gave me a brain hurt.
An Arduino Uno will consume several mA if you just put it to sleep.
Using a logic pin, once the Arduino is started, to keep the high side switch transistor on (by providing it with base current) does need a resistor in series to the base to limit current.
However the circuit will not work, when you attempt to turn off the high side switch the logic pin will be pulled to ground and this keeps the transistor switch on.
You need an extra NPN transistor in there, which you turn on with a logic high signal from the Arduino and the collector of the NPN pulls the base of the high side switch low. Then when the logic pin is pulled to ground, the NPN is off, there is no base current to the high side switch and it stays off.
Not really. The upside-down text is the worst part.
Second-worst is the lack of names on the parts. Names like R4 and Q2 are really important so that we can discuss the circuit, instead of "the second diode on the right."
Then there's more cleanup that could be done, such as using ground symbols but that isn't interfering with understanding the diagram at this point.
So,looking at the circuit, you have two 3V batteries in parallel, feeding through a series of diodes to the Uno's barrell jack, which itself has a series diode. Each diode drops 0.7V, so how could this possibly power an Uno which requires 5V?
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.
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?
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.
