View Full Version : Power Strip controlled by a Parallax Basic Stamp...

02-09-2005, 11:36 PM

I have been looking for ways to build a power strip where each outlet is controlled separately via my Basic Stamp 2.· When Googleing the other day, I ran across the following linke:


This is exactly what I've been looking for and he used the Basic Stamp 2, except I don't really need the X10 features, just a basic RS232, simple command set that can be sent from a character terminal to reset the device plugged into that specific outlet.· However, all links from the page lead to nowhere land, including the person's name associated with it.

So, my question is, does anyone have or know where I can find schematics for something similar that I can study and have something to go on?· I am not looking to build a product and sell it, I am simply looking to solve a problem I have in which the current products on the market are WAY beyond my budget...·

Any help would be greatly appritated...http://forums.parallax.com/images/smilies/smile.gif

Thank You,
Mike Marshall

Paul Baker
02-10-2005, 12:24 AM
can't give you a specific schematic, but power switching is typically done with relays or triacs, both will need a mosfet to drive since they require a higher current (and frequently a higher voltage) to operate than a stamp can directly handle.

02-10-2005, 04:08 AM

"...power switching is typically done with relays or triacs, both will need a mosfet to drive since they require a higher current (and frequently a higher voltage) to operate than a stamp can directly handle."

I've Googled that a bit, and came up with a doc indicating that relays/triacs are the equivalent of a solid state relay... Is that correct?·

Also found the following:



What do you make of this procedure?· Does it have enough isolation to protect the Basic Stamp?

Also, the procedure indicates that I can run 16 relays off of the Basic Stamp II... That would be great, if it would work...

Thank You,


Paul Baker
02-10-2005, 04:44 AM
Yeah the links you gave are what I was getting at. Solid state relays could also work, I've heard people gripe about them, namely thier mean time to failure but have not personally used one myself.

The 2N2222 is pretty old school, you may want to get a more modern transistor, most designers nowadays will use a n channel mosfet like Jon shows here: http://forums.parallax.com/showthread.php?p=521472 but keep the diode across the relay like your link shows.

Also be sure your relay, triac or SSR can handle the amps needed by anything you plug in the outlet. You'll likely want to put a fuse in the load line to prevent too much current from being drawn.

Did you want individual control of each outlet or all are in the same state?

MOSFETs have the benefit of having no needed bias current like a bipolar does (in steady state, but it will consume power when your switching it on or off), the only current consumed with be through the bias resistors and you should be able to drive several mosfets in parallel of the same gate voltage point (the only limitation to the number of mosfets you can connect in this manner is the max switching current required to switch all of them). All this is only an issue if you drive all the mosfets together (not individually controlled).

Finally the schematic in you link uses a 5V relay, be sure if you use this configuration, you get that type, if you get a 12V or other type of relay, you'll need a seperate supply to drive the relay. And like he says you'll need a regulator·better than the·stamp's·to drive the extra current of the relays. using a seperate regulator for the relays will help further issolate the stamp from the switching elements, but all negative supply lines should be tied together (Vss of stamp aka Ground).

All these methods should provide enough isolation (there are some non-isolated triacs though).


Post Edited (Paul Baker) : 2/9/2005 9:48:33 PM GMT

02-10-2005, 05:09 AM
MIKE mlm001



02-17-2005, 03:52 AM

Sorry for the delay there... Got pulled in another direction...

Thank you for the post reply...

Hey, I was looking at the DigiKey catalog yesturday at the triacs, and I've found something called a SCR...· Seems to be a varient of the triac...·

If you or someone has time, could you recommend a DigiKey partnumber for a triac that would be capable of switching:

Max· 15AMP 120VAC
On or Off only (not a dimmer)
I will be basically building a power strip, where I will be controlling each 120VAC outlet separatly via the Basic Stamp 2.·

Any help would be greatly appricated.

Thank you,


Paul Baker
02-17-2005, 04:03 AM
A Triac is a bidirectional version of an SCR, Triacs typically are two SCRs tied together in opposite directions. SCRs have a more limited functionality because a SCR once activated will stay activated until the power running through the SCR is cut. Triacs also have this behavior but because AC power is ussually used through them, they automatically shut of when the voltage crosses 0. As per your request, yeah Ill give you some help within the next day.

Paul Baker
02-17-2005, 11:29 AM
Ok check out this reference: http://www.epanorama.net/circuits/semiconductor_relays.html
down the page they talk about using triac to control AC power and give a bunch of information regarding safety as well. The example circuit given, they suggest choosing a suitable optocoupler to provide a logic level interface. This will also provide the proper isolation between your controller and the AC main. As far as a choice of a triac I would go for the Q2016LH4 a 16A max, or if you want to overdesign it a bit go for Q2025L6 which is a 25A max triac for about half a dollar more.