Hi, I'm trying to use my Arduino Uno to "click" a button on a remote control. My Arduino Uno runs at 5V and the remote has a 3V battery. I'm thinking of a schematic like the attached image.
On all examples that I've seen the transistor never "drives" a circuit with a lower voltage than being applied to the base. Is it possible to do like I'm trying to do?
The leds and the battery in my schematics would be the circuit that I want to close to simulate the button click.
![2015-04-02 10_48_33-Untitled Sketch 2.fzz_ - Fritzing - [Breadboard View].jpg](https://europe1.discourse-cdn.com/arduino/original/3X/c/9/c994c63ce0ff957fc0e7072f69b74f4c1132925a.jpg)
Your circuit doesn't make much sense. Nevertheless:
To activate a button on a 3V remote control, you use a 74HC4066 - quad bilateral switch. Ground and 5V of this device go to the Arduino, Arduino outputs control its four enables. You can either connect Arduino ground to your 3V negative or Arduino 5V to your 3V positive but of course, not both. The two terminals of each "switch" in the device can go across a given button on the remote; you have four available functions.
Note that the Arduino supply must always be on if the 3V supply is to be present. You should also put 47k pull-downs on the enables so that they are "off" if the Arduino is in reset.
Thanks for the reply. Is it impossible to do what I want with a transistor? I've attached a simplified
schedule (I hope it makes more sense :
). All I want is to short circuit the button on the remote by setting Pin 8 HIGH.
mcwarhol:
Is it impossible to do what I want with a transistor?
To answer that, it all depends on the circuit in the remote. Tage a good, clear picture of the internals so we can have a look.
In case of few buttons that all share a single, common connection, a transistor may do the job. In the case of a multiplexed design, it's not that easy.
Again, a good, sharp picture says more than 100o words. Please remember to crop and re-size the picture so it's no more than 1024 pixels on the longest side. People don't want to download ginormous pictures without any reason.
// Per.
Ok. I have now attached two images of the remote. In one of them you can see a red and a black wire. These wires are connected to a relay to "press the button". In the other picture you can see the remote with the buttons removed.
The thing is that I would like to use a transistor instead of a relay. I would like to connect the red and the black wire to the transistors collector and emitter.
Zapro:
In the case of a multiplexed design, it's not that easy.
Which would be why I described a reliable and easy way to do it. 
The contacts (the switch part) of a reed relay could be used.
There's no issue of polarities and so on, wire the relay contacts in parallel with the pushbutton.
Simple.
Here's an example (nevermind the wire3 and camera_gnd labels) --
I see that while I composed this that you had posted about a config using a relay. Oh well.
mcwarhol:
Thanks for the reply. Is it impossible to do what I want with a transistor? I've attached a simplified
schedule (I hope it makes more sense :
I don't assume a lot in such matters. Is it N.O. or N.C.?
Is the remote's switch making an open/close to Gnd?
Or is it an open/close to +V.
It makes a difference (deciding what, whether, or how.)
mcwarhol:
Ok. I have now attached two images of the remote. In one of them you can see a red and a black wire. These wires are connected to a relay to "press the button". In the other picture you can see the remote with the buttons removed.The thing is that I would like to use a transistor instead of a relay. I would like to connect the red and the black wire to the transistors collector and emitter.
OK, I don't give you credit for the photography - better to take the thing out into bright daylight and use a proper camera either with its "macro" function, or at least a metre away and with its maximum zoom to get a perfectly focused photograph.
Nevertheless, you appear to have identified that one terminal of each switch is indeed connected to the negative of the battery. In that case, yes, a simple general-purpose NPN transistor can be connected with its emitter to that negative terminal, its collector to the corresponding switch terminal, and its base through a 1k resistor to the control output of the Arduino given that the Arduino ground is connected to the battery negative of the remote.
Yes, simple and effective.
