I'm trying to make a small device connected to PC and I don't want to use the Arduino board (it's too big and... let's be honest - too expensive to leave it inside the PC :)).
I need the simpliest connection diagram of Arduino which I could connect to PC via this USB-RS232 adapter (PL2303 based). I just want to have the basic features - reset button, power LED, of course ATMega and all the pins. And communication with the PC.
I thought of something like this:
(forgive me that, it's my first "anything" in Eagle)
But I found the Single Sided Arduino schematic and I see the serial connection is more complicated.
But... in the Standalone tutorial there's of course different USB-RS232 adapter, but the connection is pin-to-pin without complications.
Do I have to put those transistor-capacitor-diode-resistors combination on the TX/RX lines?
Second question - can I just power it with the 5V from USB via adapter, or the voltage regulator is absolutely necessary?
I'm prepared to be way off here, but I think the transistor/cap/diode stuff is to do with shifting TTL to RS232 levels. For a USB board, you wouldn't need them.
Similarly you can take power from the adaptor, the VR is normally when you're using an external supply such as a "wall-wart" or mains adaptor for us non-Americans...
You are better off with a different RS232 to USB adapter. When you convert
to RS232 you need to add the transistors to level shift. If you convert to RS232-TTL
you won't need the transistors. There are a number of FTDI interfaces that convert
to RS232-TTL. They are more expensive.
The reset circuit is not correct. You are shorting the 5V to GND.
You should be able to power the device from the USB 5V without the
regulator as long as the operating frequency is not too high.
You can defnitelly power it directly from the 5V USB, just add in a decoupling cap of 100nF across Vcc and Ground and make sure you don't pull more than 500mA. Also check out your Reset connection as mentioned because when you press the button its a direct short.
As for USB to serial Adaptors all of them output RS-232 Voltages levels so the simplest would be to get a MAX 232 line transceiver which will convert the RS 232 level back forth to TTL levels which is what the ATmega uses.
Don't worry about anything else because this should work if you use a MAX232 which will be cheap, simple and reliable. If you are going to try and level shift with discrete components you are going to just spend time getting it to work right.
I've made several single sided boards. My spirograph project is single sided with a few shielded wires going to the hbridge. I use the sparkfun USB adapter (5v) to program the board. If you want to add the auto reset without having to add the pushbutton add a .1uf cap. If you want to look at just the brd file I can send you one ;).
Of course RESET is wrong. I didn't notice it - trust me, I'd never done that in purpose Thanks.
By the way, I'm sure it went wrong when I was trying to learn about connecting elements in Eagle (wire is not enough, junction is needed... Electronics Workbench didn't have that kind of complication :D)
As for the cheap small boards, the 18$ is not very cheap for me, because PLN/USD isn't very good. Here, when I buy components and make my own PCB, I can do all of that for about 7$ and 4$ for the adapter. 12.5$ from ModernDevice is a quite good price, but the shipment to Poland will be the same or even more
As for the cheap small boards, the 18$ is not very cheap for me, because PLN/USD isn't very good.
Note that some of the small cheap boards are open-source in one form or another, so that even if it isn't practical to buy the kits or bare boards, the designs may be a good starting point. The "Really Bare Bones Board" was placed in the public domain, for example, and I did a single-sided EAGLE-based version that is also PD. http://www.instructables.com/id/Single-Sided-Really-Bare-Bones-Board-Arduino-in-EA/
in the Standalone tutorial there's of course different USB-RS232 adapter, but the connection is pin-to-pin without complications.