[GreenKeys] Arduino Project on Hackaday

[Ralph Irish]

I'm surprised NOT to see MOVs mentioned as 'snubbers'. They are compact and 'non-polarized' 
and seem to be available in a wide range of 'clamping voltages' and power ratings. A relay device 
I designed onto a PC card (not relating to RTTY) has provisions for two of them to accomodate 
each side of a SPDT contact arrangement. Don't know how many have used them though. The 
"DEMO" I have runs from three 9V batteries since small, compact 24V batteries don't seem to 
exist. Since my 'load' in the DEMO is just a #328 bulb, I am not worried about contact erosion. 
(Batteries have lasted for close to 8 years now.) 

Ralph - W8ROI 

- - - - - - - - 

From: "Ralph Mowery" <rmowery28146 at earthlink.net> 
To: greenkeys at mailman.qth.net 
Sent: Thursday, February 13, 2020 10:22:05 AM 
Subject: Re: [GreenKeys] Arduino Project on Hackaday 





My 2 main concerns would be the voltage is somewhat high for the relays, but running around 100 volts is probably ok. As someone pointed out, a snubber of some sort may help with the relay contacts arcing. 

The other is that the relay may not be able to switch fast enough to keep up with the teletype signals. Probably a better relay would be in order or even better would be a transistor like in the ST-6 with the RC network across it. The program may or may not need to be slightly modified to invert the output signal. 



There have been many ideas for the power supply. I put together one a few years back that uses a 12 volt wall wart (voltage not very critical) driving one of the China voltage converters that puts out about 90 volts and a resistor large enough to limit the current to 60 ma for my loop. 



Ralph ku4pt 








From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Jeff G 
Sent: Thursday, February 13, 2020 12:12 AM 
To: greenkeys at mailman.qth.net 
Subject: [GreenKeys] Arduino Project on Hackaday 





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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