[GreenKeys] Arduino Project on Hackaday

Thu Feb 13 13:00:02 EST 2020

> Here in the 21st Century, I don't understand all this angst about relays. 

I was kind of thinking the same thing re: solid state relays. I abandoned the search for a suitable electromechanical relay for high voltage DC a long time ago, though I personally love hearing the telltale "click" and "clack" as it's engaged and released-- there's something to be said about the aural experience (hence part of why heavy metal is so entrancing). I still use electromechanical relays for AC voltages and get my fix that way.

I've been using knock-off Foteks with my 120VDC loops for a couple years now, but just for loop power control, not for signaling. The signaling optoisolators in the Volpe boards are obviously meeting and exceeding expectations, too.

One of the Foteks failed the instant I powered a loop up, but the others have been going strong. I ordered extra because I knew knock-offs were likely to have duds. But at a few bucks a pop versus $30 to $40 for genuine, the winner for my application is clearly the device that does pretty well 99% of the time even though the other would be 100%.

-
Jordan Spencer Cunningham
teletype.net | GreenKeys Search Engine: teletype.net/gksearch
SMS via teletype: 385-308-4898 | Email via teletype: tty at nerdology.org

On Thu, Feb 13, 2020, at 9:28 AM, Al Klase wrote:
> Gang,
> 
>  Here in the 21st Century, I don't understand all this angst about relays. Use a solid state device as suggested here: <http://www.aetherltd.com/connecting.html>
> 
> Devices like the HSR412 <http://www.farnell.com/datasheets/87286.pdf> do the job admirably, and cost very little money. Ebay from China.
> 
>  Al
> 
> On 2/13/2020 12:45 AM, Harold Hallikainen wrote:
>> Interesting project. It "bit bangs" the serial data out. It looks like the
relay specified (version 2) is obsolete. The datasheet on it (
>> https://www.seeedstudio.com/Relay-shield-V2-0-p-1376.html ) says "Do not
operate voltage more than 35V DC." Otherwise, there are no specifications
on the relay.

Relay version 3 at https://www.seeedstudio.com/Relay-Shield-v3-0.html .
This one does have specifications of:

250VAC/30VDC
Switching Current:	15A/7A

With DC, they are concerned about arc quenching, so the voltage rating is
much lower.

The project page says to use a "current limited power supply" of 300V, 20
mA. I'm used to using much lower voltage (maybe 100 to 150) with a series
resistor to set the current. Also, 20 mA is good for series holding
magnets only. For pulling magnets or parallel holding magnets, 60 mA is
required.

On the relay voltage, there are a couple concerns. One is the contact
voltage rating (how high a DC voltage can it break). The other is the
insulation resistance and breakdown voltage to the remainder of the
circuitry. It'd be nice to not send a hundred volts or more into the chip
I/O pin! It might also be nice to add an RC snubber circuit across the
relay contacts to reduce arcing (like the snubber across a Teletype
keyboard).

So, it will probably work, but it would be nice to use components within
their specifications.

Harold
>> http://w6iwi.org

>> 
>>> Not sure if this was discussed here before, but I'm curious to throw this
to the wolves, er experts. I was sent this project on Hackaday, and having
a Model 32 around I slapped it together and tried it out. Lo and behold,
it
actually worked great. (To be clear, it's not my project)

That said I understand the cheapo chinese relays on the arduino shields
may
not hold up to switching 100+ volts DC, but just curious to ask the
experts
if there's any reason -not- to use this, even if just for periodic
demonstration purposes. I'm wondering if I could take this, and build a
basic 120v power supply out of an ISO xfmr and put this in a little
project
case for rudimentary teletype testing.

I tested it out by putting it in the loop between the teletype and my Hal
ST-6, with the ST-6 on standby, and save for an occasional glitch
(teletype
does need some love), it worked/printed fine.

Project link: https://hackaday.io/project/2836-arduino-teletype

Jeff
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>>> 
>> 
> 
> -- 
Al Klase – N3FRQ
Jersey City, NJ
> http://www.skywaves.ar88.net/

> 
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