[GreenKeys] Run teletype model 15/19 keyboard and printer on different circuits?

[sean]

Sorry if this has already been mentioned.Keyboard contacts, just like relay contacts have something called a "Wetting Current"This means to maintain a working contacts area, a certain minimum current needs to flow to naturally break down the contact resistance, and to keep the contacts electrically clean.If you have contacts that are arcing, then you have a contact suppressor problem.By going down the low voltage route you will encourage poor connections across these contacts, due to oxidisation.CheersSeanM1ECY Sent from my Galaxy
-------- Original message --------From: Mike Douglas via GreenKeys <greenkeys at mailman.qth.net> Date: 17/09/2025  20:29  (GMT+00:00) To: Windows XD <antech6586856 at gmail.com> Cc: greenkeys at mailman.qth.net Subject: Re: [GreenKeys] Run teletype model 15/19 keyboard and printer on different circuits?                 Sorry - missed the SSR detail. You are correct, no arcing worries with the solid state relay. You may need an R-C to eliminate "jitter transitions" that the SSR might be fast enough to pick up on. See the keyboard input to a PIC processor on this Model 15 interface board: https://deramp.com/downloads/teletype/Model%2015/loop%20interface%20board/Schematic%20Rev%20A.pdfOf course, you'll have to choose R-C component values that are compatible with the SSR input parameters and resistance. Have you tested the output of the SSR at speed with the selector magnet coil? The snubber circuit may slow down the transition rate below the required baud rate once actually connected to the selector magnet.Mike D                                                                                                        On Wednesday, September 17, 2025 at 12:53:13 PM CDT, Windows XD <antech6586856 at gmail.com> wrote:                                                                                                            I see, I'll keep that in mind if 5v does not workWill that still happen with a solid state relay? I thought those didn't use magnets and instead used a photocoupler or something similar.On Wed, Sep 17, 2025, 9:36 AM Mike Douglas <deramp5113 at yahoo.com> wrote:                I have found I had to go to 12v-15v across the keyboard to get reliable operation across a variety of machines. 5v may be OK for a given keyboard if its contacts are in good shape and show low resistance (< 1 ohm) when closed.Directly running a relay coil with your keyboard isn't going to totally solve your arcing problem since the relay coil voltage will also build to the point it discharges via an arc across the keyboard contacts whenever a switch opens. There will be less energy stored in the relay coil than in a selector magnet coil, but you'll still get an arc. If you build a snubber for the relay coil, you have to be sure it still allows the relay to switch fast enough for reliable 45.5 baud operation.Mike D                                                                                                        On Tuesday, September 16, 2025 at 08:44:09 PM CDT, Windows XD <antech6586856 at gmail.com> wrote:                                                                                                            Dear all,I was working on the teletype when I had an idea. I have already picked up a solid state relay capable of switching faster than the 45.45 baud needed for the teletype for something else I'm working on with the teletype, and I was wondering if it would be possible to run the keyboard on a 5vdc circuit wired to said solid state relay and have the keyboard run on 5vdc and the selector magnets at 120vdc. I can't think of any obvious problems with running the keyboard at this lower voltage, but I'd like to be sure.I'm not sure I explained it super great so I've attached a schematic, although I'm not sure if it's any better than my explanation.P.S. My keyboard has arcing problems with the contacts, will this modification coincidentally also fix that?______________________________________________________________GreenKeys mailing listHome: http://mailman.qth.net/mailman/listinfo/greenkeysHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:GreenKeys at mailman.qth.net>>> Jordan Spencer Cunningham's GreenKeys Search Tool: https://teletype.net/gksearch>>> 2002-to-present greenkeys archive: http://mailman.qth.net/pipermail/greenkeys/>>> 1998-to-2001 greenkeys archive: http://mailman.qth.net/archive/greenkeys/greenkeys.html>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.htmlThis list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.htmlMessage delivered to deramp5113 at yahoo.com                                                        
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