Hi all,
I hope someone could help me to tackle that issue..
I try to control a RC toy car using the keyboard but it does not work..
Schematic of the circuit and a picture of the setup see attached.
I just found out that the button on the RC is not connected to ground when pressed, so does that mean I need an UDN instead of an ULN?
Really appreciate your help!
BR
FD
The ULN can only sink (aka pull low) so if that's not what the remote expects then yes, the ULN is the wrong driver.
If the UDN is the right one is impossible to say unless you find out what the switches actually do.
Two pads of a button on the RC are on 3.3V and the other two are on 0v when the button is released.
When the button is pressed the previously not connected pads are on 3V. Hence, I would assume that the buttons are not getting grounded and therefore the ULN is the wrong driver?
Okay, that would seem you need to drive them HIGH. Any reason why not do that directly from the Arduino?
I just thought I need to use a driver to control the different functions (forward,backward, left, right) because there is no other option on Arduino side.
So, you mean just use the arduino to set the rc buttons on VCC without any driver would also work?
Sorry for that stupid questions...
I am a really noob on Aduino and circuits as you already recognized...
If the Arduino is also of the 3,3V type, yes. Otherwise a voltage diver (per button) is needed in order for the 5V Arduino to just supply 3,3V to the remote.
yes, it is also on 3.3v.
I will give it a try =)
I really appreciate your support!
Thx
@OP
The following is the internal structure for one section of the ULN2803 driver. You may now figure out the way of connecting your IO devices. I have added the external pull-up as an extra element.
Yeah, you can also add a (lower) pull up to counter the pull down in the remote. But I think that's a complete wast...
I just realised that the Uno has 5V on each pin...
Hence, I would need a level shifter to get the 3.3v or can I run the rc also with 5v w/o destroying it?
Whenever I see something with the title "ULN 2803 A - Wrong driver?" - or indeed, anything mentioning the ULN2x03, I automatically predict that it will be the wrong device to use. And in this case, it is most certainly wrong.
oip976:
I just realised that the UNO has 5V on each pin...
Hence, I would need a level shifter to get the 3.3v or can I run the RC also with 5v w/o destroying it?
Well, we now begin to get a "handle" on the situation. You have a UNO.
You mention some sort of Radio Control device and 3.3 V. This is quite puzzling, as 3.3 V is a voltage used for digital circuitry whereas radio control equipment uses entirely different voltages. Often a 6 V or 9 V set of batteries, possibly 3 V on a "toy" device.
oip976:
Two pads of a button on the RC are on 3.3V and the other two are on 0v when the button is released.
When the button is pressed the previously not connected pads are on 3V. Hence, I would assume that the buttons are not getting grounded and therefore the ULN is the wrong driver?
When you say "on 3.3V" and "on 0V", it is by no means clear to what you are referring. Voltage readings must be referenced to something. We need to know what that "something" is. Are you merely measuring the voltage across the switch, or to the power source of the RC controller. What is the power source of the RC controller? How are you proposing to connect it to your Arduino? Your diagram tells us nothing!
It seems we are going to have a protracted back-and-forth conversation in order to get sufficient detail to sort it out. 
