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Topic: getting rid of re-set button. (Read 732 times) previous topic - next topic

jonisonvespaa

hi
ive got a bare bones board assembled, im using a usb to ttl converter to download my programs to it, ive got a 100nf c fitted from pin 1 to gnd, i thought this mod got rid of the need of a re-set button?  mine doesnt seem to do this any ideas?
thank you

michael_x

Quote
mine doesnt seem to do this

This phrase is not complete clear to me.

You need the DSR ( DTR ) signal of your Serial  (usb to ttl converter) connected to Pin 1, and a pullup resistor, to trigger a reset before the sketch upload.
A reset button ( or a little wire to ground pin 1 manually ) is very convenient anyway.

Docedison

Also quite required unless you are the GOD of C and C++ on the Arduino... You Know... The one who Never makes a coding mistake...
I LOVE My Reset Button...

Doc

--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

florinc

Quote
ive got a 100nf c fitted from pin 1 to gnd, i thought this mod got rid of the need of a re-set button?  mine doesnt seem to do this any ideas?

The 100nF capacitor should be between RTS line of the "usb to ttl converter" and Reset pin of the processor.

JoeN

#4
Aug 06, 2012, 03:24 am Last Edit: Aug 06, 2012, 03:27 am by JoeN Reason: 1
Disabling reset for reals  is something that is done more often on the ATTiny chips to get one more GPIO pin because they have so few.  Also, it is disabled when you put the chip into debugWIRE mode, something you would never do in the Arduino environment.  Unless you need to do one of these two things, I wouldn't recommend it.  For one thing, you can no longer program the chip until you put it in a programmer a reenable that fuse.  More info:

http://www.ladyada.net/learn/avr/fuses.html

DebugWIRE is the DWEN fuse.  RSTDISBL is the reset disable which buys you an extra GPIO pin.  Setting either will buy you a lot of headaches in addition to their stated purpose.
I have only come here seeking knowledge. Things they would not teach me of in college.

CrossRoads

I think the answer is Yes, you do not need the physical reset button.  I do not install one in many of my projects.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

JoeN


I think the answer is Yes, you do not need the physical reset button.  I do not install one in many of my projects.


If that is the case, hold that pin high otherwise the ATMega will never come up.
I have only come here seeking knowledge. Things they would not teach me of in college.

CrossRoads

The question wasn't about the pullup resistor tho, just the button.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

MarkT

The chip has an internal pull-up on the RESET line.  Its a weak pull-up though (30 to 60k) so in a noisy environment an external pull-up will stiffen the signal.
[ I won't respond to messages, use the forum please ]

CrossRoads

Atmel recommends several components for the reset line, depending on the environment:
10Kpullup resistor
Diode across the resistor
cap to ground
resistor in series with reset switch to ground.

Most arduinos only have the first two.

See section 3 and 3.1 of the attached.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

oric_dan

OP mentioned a cap to ground, nothing about having the 10K pullup, which
probably should be in there.

One thing I do on my pcbs, even if not wanting a physical switch, is to include
2 pads for Rst and Gnd, where I can install a 2-pin 0.1" header. Then I can add
a shunt, and hold the Arduino in reset indefinitely. I find this to be 1000% useful.

florinc

Quote
and hold the Arduino in reset indefinitely. I find this to be 1000% useful.

Why would you need this?

Tumbleweed

Reading the OP's post, I think he meant getting rid of "using" the reset button, which florinc answered in post 3.
I always put one (.1uf cap between RTS and reset)in when using my FTDI Friend to upload sketches so I don't have to hit the reset button on every (frequent) reload.
TomJ
Einstein once said you don't really understand anything until you can explain it to your Grandmother

oric_dan

Quote
and hold the Arduino in reset indefinitely. I find this to be 1000% useful.

Why would you need this?


Many sketches blink lights or ping piezos or cycle servos, and it's a PITN
to listen to all of that going on while you're editing the sketch. Holding
in reset is easier than pulling the power plug.

Also, I often use the Arduino board's USB port to connect to other boards,
especially ones with XBee, and if you hold the Arduino chip in reset, then
you can daisy chain the RX/TX pins. [my workbench usually has jumpers
going off in all directions].

CrossRoads

Having a reset pin also comes in handy when you screw up and blast stuff out the Rx pin or Tx pin so the bootloader can't get a word in. Then hold in reset & release at the right time.
Just having Reset brought out to a header pin where you can attach one via jumper is enough to solve that.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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