Connecting an LED

I have a standalone Arduino using an ATTiny85 hooked up to a transmitter - see attached sketch.

On the data line (DAT) I don’t have a pull-down resistor (R3) installed at present.

So far it seems to work fine without R3 i.e. it only transmits when I trigger an input transmit signal.
What are the drawbacks, if any, of not installing R3?

Secondly, I want to add an LED.
I know option one will work, but to save a pin, is option 2 an acceptable method of connection? - the code will be adjusted accordingly of course.
Or will option 2 adversely affect transmissions?

I am open to any other suggestions for connecting the LED.

R3 shouldn't be needed, because an output pin sources AND sinks.
If you're worried about transmitting during bootup (floating), put the 10k across the LED.
Swapping R2 and LED (same difference) is usually safer if the LED will be panel mounted.
220ohm is rather low for a modern indicator LED. 1K is common.
VCC should have some electrolytic or tantalum capacitance.

What are the drawbacks, if any, of not installing R3?

When it is connected to nothing the input will float and transmitt rubbish which can cause interference.

Yes option 2 for the LED should work.

Thanks for the input guys - much appreciated.

If your project is battery powered, you could look for a high efficiency LED, it will use less current and so you can increase the value of R2.

Thank you for the clear and concise schematic.

Tom.... :slight_smile: