[HH] cheapest/simplest way to control a relay from a PC

[Federico Lucifredi]

Hello Tom,
  I may not have caught all that went in the thread, did anyone mention this already?

Powerswitch Tail - $25 
https://www.adafruit.com/products/268

  I like it because it is self-contained — I am all for hacking, but setting a house on fire is not the cool part of hacking. So, when using more than 18V, I do like things that come properly packaged…. cheaper than having them installed by a certified electrician, anyway :)

  When using relays, one still must take care not to overload the circuit — it is rating for some top load that, I am sure, is not adequate to start your dryer remotely.  Just saying.

 Best -F






On Nov 12, 2012, at 2:22 PM, Tom Metro wrote:

> Jack Coats wrote:
>> http://www.fullcompass.com/product/366255.html?utm_source=googleps&utm_medium=shopping&utm_campaign=googleps&gclid=CKSL0re7xLMCFao7MgodIWcA7Q
>> -- Interesting device for controlling and monitoring 2 audio lines in
>> and out.  USB controlled and powered for $30
> 
> This is a USB sound card, much like hundreds of others, although it
> claims to use 48-bit converters, which is a bit different.
> 
> In any case, not particularly relevant to the question at hand.
> 
> 
>> http://procontrol.com/products/pro-relay-4/ -- professional looking, 4
>> relay, ethernet or IR interface, POE or 1A 12V external power, no
>> price on page at first glance
> 
> Looks like it is aimed at high-end home automation and home theater
> integrators. Probably not priced to be hacker friendly.
> 
> 
>> http://www.sigma-shop.com/product/7/usb-relay-controller-one-channel-box.html?&CurrencyID=1
>> -- 1 relay, USB controlled, nicely packaged
> 
> Agreed, nicely packaged. USB-B connector on one side. 3 screw terminals
> for form-C relay contacts on the other. No relay specs provided.
> Emulates a serial port. $30.
> 
> 
>> http://numato.com/2-channel-usb-relay-module -- 2 relay, USB
>> controlled, board with exposed components assembled
> 
> No case, but you get two relays here. The down side to this one is that
> they require you attach a 12V supply (not included) to power the relays.
> (Discussion thread below the product info indicates the vendor is
> working on a version that is fully USB powered.)
> 
> The product description says the relays can handle 10 A, but the manual
> cautions that for anything over 2 A they recommend you thicken up the
> PCB traces to the relay contacts with solder. They might have well just
> used low-current reed relays, and kept it USB powered.
> 
> Nowhere do they mention what the voltage rating is on the relay. While
> most relays will handle 120 V, some don't have adequate contact spacing,
> so you can't just assume. I have a feeling they left off this spec to
> avoid any liability for inadequate high voltage isolation and lack of UL
> approval. (All of this applies to the other relay product above, as well.)
> 
> This device also emulates a serial port. The command language they
> designed seems rather clumsy, but adequate.
> 
> The manual says, "On board ICSP header makes it easy to be used as a
> development system as well." What's an ICSP header? (Aside from being a
> 6-pin header?) Ah...In-circuit serial programming:
> http://en.wikipedia.org/wiki/In_Circuit_Serial_Programming_%28ICSP%29
> 
> Not sure how that applies to this device. There's no indication that you
> can reprogram the micro on the board. Are they using it like an I2C
> interface? Based on the Wikipedia page, it looks like it is only used
> for programming, so I guess the intent is that hackers can customize the
> firmware.
> 
> 
> Thanks for digging these up. I have a bookmark folder full of serial and
> USB controlled relay products. Others include:
> 
> http://www.j-works.com/jsb315.php
> http://canakit.amazonwebstore.com/CanaKit-4Port-USB-Relay-Controller-with/M/B004JWW1GQ.htm
> 
> They're both more expensive than the ones you found.
> 
> 
>> Now $30 isn't cheap (under $2 is in my book), but these options are
>> not bad for $30 equipment.
> 
> Agreed.
> 
> 
>> Tell us what you choose, and how it works for you in your application.
> 
> I'm still in the mood to build something, so I'm pursuing that avenue.
> But I've saved the above for future reference.
> 
> I found one of my solderless breadboards that I haven't used in a long
> time, and the parts with it - a DB25 with some 22 AWG solid wire leads
> soldered on, and some optocouplers - suggests my last project with it
> was another parallel port interfacing project.
> 
> 
>> I use an earlier version of http://www.digital-loggers.com/lpc.html
>> that cost about $130.
> 
> Yes, you wrote about that on the list before as part of the PC watchdog
> thread. I never did get the Trip Lite UPS with built-in watchdog reverse
> engineered. The device I was planning to use it on worked with adequate
> reliability on a simple timer that forced a daily power cycle, so I
> didn't have adequate motivate to spend the time on it. Maybe someday, as
> it would be nice to have a $40 UPS that includes a watchdog that's
> supported by Linux.
> 
> -Tom
> 
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_________________________________________
-- "'Problem' is a bleak word for challenge" - Richard Fish
(Federico L. Lucifredi) - flucifredi at acm.org - GnuPG 0x4A73884C