Using small current to activate transistor - will any transistor work?

[JBL]

Hi.

Well I was not sure exactly how to name the thread. But here Goes.

I will try to keep this simple.

Problem and Application :

I have a Reciever Module and Sender Module in one of my projects.

One wire from the Sender sends a very small +12v constant current to the reciever to trigger it to perform a function. I had to replace the reciever unit with a new one, but now does not take a +12v current on that same wire, it works on earth trigger, so it will not do anything if that +12v current is fed to it.


Proposed Solution :

So I was thinking, OK? Use that 12v signal to trigger a relay and let the relay switch a earth tot he reciever unit. Does not work as the 12v current is not strong enough to trigger a relay coil, power a bulb or anything like that, it's 12v but can hardly give any current.

So I want to use that 12v signal to trigger a transistor, then use the transistor to feed power to activate a relay, and the relay will then switch an earth to my new receiver unit that requires earth instead of the old one that required 12v

My Question is

1. Can Any transistor work, or is there a certain current required to switch a transistor? I done it in the past on a previous identical project but forgot what transistor I used.

2. Does a relay exist that I can buy with a built in transistor, so the relay can be triggered by very weak currents?, this way it will be much neater looking. I buy most of my stuff from RS Components which I have access to here in Australia where I currently live.

3. Can I simply just use a transistor triggered by the weak +12v signal to switch earth to my receiver unit, without need to have a relay?

[stj]

Re: Using small current to activate transistor - will any transistor work?

a transistor and resistor or a cmos invertor like a 4069

[SteveNielsen]

Re: Using small current to activate transistor - will any transistor work?

Have a look at this:
http://www.rason.org/Projects/transwit/transwit.htm

[budm]

Re: Using small current to activate transistor - will any transistor work?

So the new receiver uses active low for triggering, which mean it has pull up resistor at the input so you need to pull it down toward circuit ground, then you can use FIGURE 2 of the link that Steve provided, the Collector will be connected to the control port of you new receiver. R1 value will have to be adjusted depends on the pull-up resistor value in the receiver is. Also what is the distance of the control wire will be? if it is really long, the transistor may pick up noise and causes false triggering if it used in the noisy electrical environment.