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Topic: Proofread Schematic with 644p with MAX232 (Read 3488 times) previous topic - next topic

codlink

I need to see if this schematic is correct to use an Atmel 644p standalone with the Arduino IDE.  I have went over several schematics with a MAX232 but, some have resistors between the USB jack and MAX232.  None of them explained why they are needed. 

Any advice and constructive criticism is welcome.

Thanks!
//LiNK

retrolefty

I think you are terrible mistaken in your proposed use of a MAX232 type RS-232 to TTL voltage converter chip to use as a USB type serial converter chip like a FTDI FT232RL. The USB connections to a PC can only be used with a chip that can enumerate and function as a USB device, which a simple voltage translator chip like a MAX232 is most certainly not.

Lefty

CrossRoads

Caps on MAX232 are not correct.
Should be 5 total - you only have 3.

MAX232 does not do USB to Serial - you need a part like FT232RL for that. See www.ftdichip.com
I would suggest a module like MIKROE483 from mouser.com $11
Also FTDI Basic or FTDI Breakout board
Or CP2102 module from e-bay, use the BATI kind that have DTR available at a breakout hole.

MAX232 will output +/-10V signals, and expects the same back.  As drawn, T2out will blow up the Rx pin. And R2out will likely damage a PC if connectedl.

Put a diode across the reset resistor - anode to Reset, cathode to +5v.
What does cap C9 connect to when the jumper is closed?
C4 should be bigger, like 1 or 10uF.
C8 can be 1uF.

Add 0.1uF caps to the VCC, AVCC, AREF pins, as close to the pins as possible.
Can draw the VCC/AVCC parts next to C5.

JP5 - RTS should be DTR, I imagine you want it going to  C9.
Check the order of the pins, make sure an FTDI Basic, or FTDI cable can plug straight on. I always double check against the ProMini schematic to be sure.

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.

codlink

Wow, ok, learn something new everyday..

Attached is an updated schematic.

Thanks Crossroads
//LiNK

CrossRoads

Flip over diode D1. The intent is for any spikes/etc. on the reset line to get bypassed into the Vcc line.

Planning to connect some external parts to this? I would add another header or other means to connect +5, Gnd to off board devices.
The FTDI and AVR header can be used as well.
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.

codlink


Flip over diode D1. The intent is for any spikes/etc. on the reset line to get bypassed into the Vcc line.


Oh, ok... Must have misinterpreted what you wrote...

Quote

Planning to connect some external parts to this? I would add another header or other means to connect +5, Gnd to off board devices.
The FTDI and AVR header can be used as well.


Yes, I wanted to get the basics first.  This board is to experiment to see how the 644 will do in a bigger project.  Wanting to learn more about standalone micros before I make any PCBs for the larger project.

Thanks for your help CrossRoads.
//LiNK

CrossRoads

Well, you could always 'hack' your Uno  :D
Here's one of the early things I did with arduino, adapting an Uno to work with a '644P.
The larger memory and dual serial ports were needed.
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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