USB Relay Controller Help

[KI6ZON]

Hello-
This isn't exactly ham radio related, but I am hoping someone can help me.

I bought a USB I/O Board and Relay Controller from Electronics-DIY.com (the specs are here, purchased here) and I got it built. The problem I'm having now is in connecting the relays. It's an 8-channel controller, and it included 10 1k ohm resistors and 10 BC549 transistors, intended to be connected to the output pins. However, I can't figure out how to connect them. Can anybody offer any suggestions?

Thanks!

-Sutter KI6ZON

[KF5FEI]

Looks like those transistors are typical general purpose NPNs -- here is one example -- scroll about 1/2 way down the page.

http://www.kpsec.freeuk.com/trancirc.htm

Here is another example:

http://pcbheaven.com/wikipages/Transistor_Circuits/

Although not provided, you definitely want to use a flyback diode when switching a relay. Might want to try the circuit with an LED first, just to get the hang of it.

[KI6ZON]

Okay, I think I'm understanding it better, but to clarify: When there's voltage across B and E, the voltage will pass between C and E, correct? And how does the flyback diode work?

Thanks!

-Sutter

[KF5FEI]

The diode protects the rest of the circuit from voltages generated by the collapsing magnetic field in the relay coil when power to the relay is removed.

Transistors are a current device -- if you have a current flowing from the base to emitter, it will switch the transistor on and current will flow from the collector to emitter. The resistor between the base and the pin on your circuit limits the current to the base of the transistor.

One thing to consider is the amount of power a USB cable can supply -- it might run one relay OK, but more than one relay may pull too much current and cause an issue. If they have a forum or user group for that particular line of products, there are probably examples of circuits using external power for the relays.

[KF5FEI]

Here is another link:

http://www.dnatechindia.com/Tutorial...ontroller.html

[KI6ZON]

I've almost got it - thanks for your help. Does it need to be a specific type of diode?

Thanks!

[KA9JLM]

I've almost got it - thanks for your help. Does it need to be a specific type of diode?

Thanks!

I use 1n4007, but any 1n400X type will work.

Any silicon diode is better than none.
.