Anything wrong with this circuit?

Other Hardware General Electronics
1

I'm using 49MHz transmitters and receivers from toy cars to trigger Arduino Nanos because they're so cheap and easy to use. All I need is just a remote push button, and I don't need separate frequencies for separate projects as I only use one project at a time.

The output of the receiver is a standard motor driver chip I assume, and neither of the two output pins ohm out to ground. So I'm thinking that I cannot connect one output to ground and the other straight to Pin 2 of the Nano.

So I'm using an opto-isolator which allows me to set up a common ground, and a high and low state. I don't need the isolation feature of the opto-isolator, so I don't need to isolate grounds or power supplies.

Do you see any problems with this circuit? (Yes, I know there should be a resistor at Pin9! But I actually have stuff connected other than an LED...I just added that as a visual.) (And I see that I have mistakenly shown a ground going to the opto body, which is not really there...)

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2

Two definite problems

  1. No current limiting resistor on the receiver out-opto LED
  2. No current limiting resistor on Nano output LED

One possible problem

  1. 5V/150 ohms = 34mA. Can the opto output transistor handle 34mA?
3

Thanks for your input adwsystems! (The output doesn't see all that current (the opto doesn't turn on completely), but good point, and it can handle it.)

4

callmebob:
the opto doesn't turn on completely

If the opto output transistor isn't turning completely on then you risk not dropping below the nano Vil level to detect a '0' level.

5

the opto doesn't turn on completely

Use a 10K load resistor for the optoisolator output.

6

Thanks to you all for your input. I got a private message from someone who preferred to do it via private message rather than on the forum, but he helped me with the following info which worked out great:

"Whether or not the outputs "ohm out to ground" is completely meaningless. It would be foolish to connect any to ground as this is clearly an "H-bridge" which drives one to ground and the other to Vcc or the opposite, depending on which way the motor is supposed to go. If you are going to use the same 5 V power supply for the receiver and the Arduino, just connect each to an Arduino pin via a protective 4k7 resistor. One will go high for "forward" and the other for "reverse". ...just lose the optocoupler."