On standalone projects, is reset switch necessary? Is there any difference between power recycle and reset?
Lavan:
On standalone projects, is reset switch necessary? Is there any difference between power recycle and reset?
That depends more on the project than on an actual need. You need, however, to keep the RESET pin high all the time, so you have to take that in consideration. As a rule of thumb it is a good idea to protect the reset pin with a 10K resistor + a diode (a 1N4148 will do). Check the UNO R3's schematic here: http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
If you want to be able to reset your standalone board, then all that will be missing is the button (taking RESET to GND). I find a good idea to be able to reset my standalone projects.
I am currently working on a standalone project and the board has only 1 serial port for the bluetooth dongle (4-pin header), 1 buzzer, 1 socket for a LDR that will be 50cm away and a 7-pin header for the daughterboards holding LED matrices. Neverthless, I added a reset button to the board, a voltage regulator (LM7805), a 6-pin header for serial programming using a FTDI adapter, and a ICSP header. This little board will be in my car, powered by the car's cigarette lighter.
If you plan to leave the bootloader on your chip to reprogram the code, you'll be happy when you realize how much easier life is with a reset button.
OK thanks. I understand I need to keep the reset pin to high using a pull up resister. So the question is, power recycling the board is not going to reset? Power recycling is not just like reset? Just curious to know.
Lavan:
OK thanks. I understand I need to keep the reset pin to high using a pull up resister. So the question is, power recycling the board is not going to reset? Power recycling is not just like reset? Just curious to know.
Yes a power down/ power up cycle generates a reset condition just like using a reset switch. So if you are programming the chip external to the standalone circuitry and then plugging the chip into a socket on the standalone board then you do not require a reset button. Your choice.
Lefty
Thank you!.. I got my question answered.
I typically leave reset off, just connect one via jumper to a header pin if needed for initial development.
With ICSP header and DTR on Serial interface header, have 2 places to connect to.
When I make a stand-alone board I don't usually bother with a reset switch, because power cycling does the same thing (almost the same, I think the processor sets a slightly different status bit).
And you can reprogram with an FTDI connection as long as you have a (0.1 uF) capacitor in series with reset, and with ICSP with no extra components because the ICSP pins bring out reset which the programmer brings low for programming.