[GreenKeys] Arduino Project on Hackaday

[Al Klase]

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 relay specified (version 2) is obsolete.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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