auto reset an Arduino using ftdi - DTR signal stays low and needs to go high after 1-50ms - Electrical Engineering Stack Exchange


hello have cheap ftdi going recreate on pcb can flash atmega2560 chip onboard, ftdi has dtr line pulled low when sequence starts stays low instead of going low high after 1ms 50ms, need find out how create simple circuit when pulled low goes high, how can this, have simple components hand.

my stocked parts:

103 ceramic caps

25uf aluminium caps

220uf aluminium caps

some blue ceramic caps labeled "10"

practically common resistors values

5v zener diodes

5v switching diodes

npn transistors

n channel mosfets

5v reflecting diodes

can make using ? else can what's needed.

many thank edwin

sorry it's atmel atmega 2560 chip on pcb have serial lines , reset,5v,ground , 2 gpios on pin out. can flash ftdi. , ftdi dtr line stay low , need pluse rest line need figure out how use low signal pull reset low high right after.

if try on arduino mega or uno holding down reset not work it's pulse going low high load boot manager. hence dfti dtr staying low not work if directly connected rst.

this schematic of arduino pro mini , take @ reset mechanism:

enter image description here

there 2 ways reset device: holding down reset push-botton/switch or driving line (dtr or rts) low.

note: applications arduino use dtr, others use rts, both seem work. i used rts , had no issues.

now, reset. when dtr/rts pulled low, capacitor, \$c_2\$, starts charge 0 \$v_{cc}\$ value. asserting reset, because time takes reach logic 1 (maybe 0.7*vcc), enough micro interpret logic 0 (up 0.3*vcc).

also, ftdi applications use pullup resistors connected dtr/rts lines since these open drain. one:

enter image description here

the pullup not mandatory in case because pro mini, has 1 on board on reset pin, doesn't hurt either.

like said, dtr or rts may work, speaking based on personal experience that's how got work. also, seems arduino supports use of either, test out , see happens.

i found images on sparkfun website. ftdi image 'ftdi cable' uses rts line. 'ftdi breakout' board, call on there, uses dtr line instead , no pullups...

arduino pro mini

ftdi cable

ftdi breakout board


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