Interfacing pins to control an RC controller

Hi, I'm trying to piggypack an arduino on to a RC car controller. The controller takes input from 4 momentary switches, and I'd like to be able to attach a pins to all of them, to be able trigger each switch.

After probing around with a multimeter/battery, it turns out that the switches control the flow of negative voltage across them, so I can't use the default digitalWrite method to toggle them.

How this works:

O ---Toggle--- O
^negative voltage here and it acts as if the is switch turned on

I think I could bridge a transistor across the switches, and then toggle them that way, but I don't have any transistors lying around.

How would I be able to generate this mystical "negative voltage" to toggle the switches? I heard it has something to do with PWM.

Disclaimer: I have little understanding of most electronics stuff, I'm a software guy.

The simplest way is to use four small 5vdc relays. You can drive the relay coils directly from an Arduino pin as this one below only draws about 10ma. Wire the relays contacts across the switch contacts on the controller. Simple, no? Not too expensive at a buck a piece.

Lefty

Ok, how would I do it without external hardware though?

NONO thats definitly not the easiest way!!!! Your using the ground from the RC controller thus connect a arduino pin to the side of the switch that is being switched to ground and then set the pin LOW when you want it to be connected to ground... when its low the ground current will flow thru it and thus the same ground as if the switch was being triggered

Ok, how would I do it without external hardware though?

I wouldn't be prepared to even say it's possible without external components without a schematic of the controller to study.

Lefty