Hello, thanks for your attention.
I am a beginner with arduino, and I am trying to program an ATtiny85 using its ISP mode. In every single tutorial I find, people use a 10 uF capacitor between the reset pin and ground of the arduino, but no one explains why.
So, my question is, why is it necessary? Thank you!
Used to disable the auto-reset circuit.
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LarryD:
Used to disable the auto-reset circuit.
of the Arduino used as programmer. Because you don't want that to reset when you start programming because it needs to talk to the ATtiny.
I have actually put a slide switch on the interrupt pin so I can easily disable it. No 10uF caps needed if you do this.
Wao, okay, so I understand that the first thing arduino does when a new sketch is loaded is to reset itself, and introducing this capacitor makes this task imposible because some reason, am I right?
Yes. And the "some reason" is that it just receives a small pulse and the capacitor creates a RC-filter.
The autoreset circuit is a 0.1uf cap between reset on the '328p, and DTR on the serial adapter. DTR is brought (and held) low when the serial port is open. The capacitor turns this into a pulse on reset (the R in the RC is the 10k pullup on reset), which resets the '328p - that causes the bootloader to run, this is how you can program the Arduino over serial without manually resetting it.
Obviously, there are cases where you really don't want it to reset when you open connection to serial port. The 10uF cap is the quick way to disable it - this cap is much larger than the 0.1uf one in the autoreset circuit, and will prevent it from generating the reset pulse.
and will prevent it from generating the reset pulse.
Well in fact it is a low pass filter and it will swallow or block the tiny high frequency pulse.
Thank you guys, that helped a lot!
Grumpy_Mike:
Well in fact it is a low pass filter and it will swallow or block the tiny high frequency pulse.
With all the talk about an AVR requiring a series resistor in order to safely drive the picofarad level load produced by a mosfet gate, I'm amazed that hearts don't literally seize up and die at the thought of shorting a reset signal with a 10 uF cap.......
The reason is that the reset pulse is coming from the serial drivers in the USB to serial converter not the processor.
Grumpy_Mike:
The reason is that the reset pulse is coming from the serial drivers in the USB to serial converter not the processor.
You know exactly what meant.....