relays

aggiewhat

I am tring to control a 120 volt lighting fixture with my BS2, do you have any recommendations on relays to use, and where to get them?· My problem is that most relays that are rated for 10amps @ 120V have a 12 volt coil voltage, where the BS2 outputs only 5V.

If there are no reasonable relays that can be controlled with 5V, is there a way to step up the voltage on the output of the BS2?

Thanks.

AlWilliamsAWC

There is an article about driving relays at http://www.wd5gnr.com/stampfaq.htm in the hardware section.

Here's the simple way to do it for a relay with coil currents up to, perhaps, 75 or 100mA.

1. Connect one end of the relay coil to +12
2. Place a 1N4001 diode across the coil so that the band points to +12 and the other end connects to the other side of the coil
3. Connect the other end of the relay coil to the collector of a 2N2222 transistor.
4. Ground the 2N2222 emitter
5. Connect the base of the 2N2222 through a 1K resistor to a Stamp pin

Now when the Stamp pin goes high, the transistor will conduct and the relay will turn on. Don't forget the diode or this will only work once.

Hope that helps.

Regards,

Al Williams
AWC
Easy RS232 Prototyping
http://www.awce.com/rs1.htm

aggiewhat

is there a particular relay you recommend for 120V lighting control?

AlWilliamsAWC

I should have mentioned, have a look at http://www.awce.com/kp1.htm. This will do it all for you -- 5V conversion, diodes, etc. I had forgotten about them :-)
·

Brian Miller

Not to highjack the thread, but I was wondering if the transistor is required with a solid state relay. Pacifically this one.



http://oeiwcsnts1.omron.com/pdfcatal.nsf/PDFLookupByUniqueID/3D7C325F64A566B886256D35004E5AF7/$File/D20G3NE0503.pdf?OpenElement

Newzed

You should use a Darlington array or a Darlington transistor to drive any relay.

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Sid Weaver
USB-powered Stamp Board

http://hometown.aol.com/newzed/index.html
·

Jon Williams

Brian Miller said...

Not to highjack the thread, but I was wondering if the transistor is required with a solid state relay. Pacifically this one.



http://oeiwcsnts1.omron.com/pdfcatal.nsf/PDFLookupByUniqueID/3D7C325F64A566B886256D35004E5AF7/$File/D20G3NE0503.pdf?OpenElement

If you use the zero-cross version then yes, you will need some sort of buffer.· The spec for the zero-cross version says the input impedance at 5 volts is nominally 250 ohms; that means it would take 20 milliamps to drive it.· While the BASIC Stamp can handle this, you wouldn't have any margin left on the pin group, and the spec allows the impedance to go down to 200 ohms; to big a load for one pin, really.

If you use the without the zero-cross function then you'll have no problem; the input impedance is spec'd at 300 kOhms.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

Brian Miller

Opps, ordered the wrong one! Guess, that will be another addition to the misfit parts box.

Still a beginner here, Thanks for all the help.

so your saying....

5v / 250ohms = .02mA With Zero cross

5v / 300000ohms = ??? (a really low mA rating safe for stamp pins) Without Zero cross

Jon Williams

Yes, that's what the docs say.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

ChipCircuit

As for relays, check Jameco for a variety of reasonably priced ones. Many different voltages available and some are as low as 99 cents.

Dave