Transister as relay?

[riddler]

Hi Guys..

Sorry if this is a dumb question, but realy struggling to find answer.

Right here we go!!
a few years ago, for an alarm system, i needed a small component to convert the dc 12volt (low current)positive signal from a vehicle door contact,
to a dc 0 volt signal,
A guy at a local component store (no longer there) sold me, from what i can remember a Mosfet transister, and showed me how with just this single component
will do what i needed, and it did..

Problem i have is i cannot remember the exact component or how he wired it.
and i need to do the same thing again,

so if there is anyone who can help,

please help me.


Thanks in advance Julez.....

[fish]

Old post is old.

If I understand you correctly, you're trying to make an inverter.

Put a 5.1V Zener diode between the signal pin and ground. Connect to the base of a NPN transistor through a 1k resistor R1. Connect a 10k resistor R2 between 5V Vcc and the collector, and then connect the emitter to ground. You should find that between R2 and the collector of the transistor, you have signal which is 5V when the input is 0V, and 0V when the input is 12V.

Have a look at the last circuit on this page:
http://www.kpsec.freeuk.com/trancirc.htm