[GreenKeys] inexpensive loop supply transformer wanted

[Ralph Mowery]

While I would not usually recommend it, you may want to just use a 24 volt transformer and parts for that voltage.  Feed a bridge and you get close to 30 volts and you need a differant resistor...

At those voltages, you can  probably use a 7805 voltage regulator configured as a current regulator instead of a voltage regulator. That way you do not have to worry about a high wattage resistor.


>From what I understand from your message this will just be a local loop and not off the radio.  You will get a bit more distortion of the loop current, but just to drive one machine at a time and locally you should be fine.

  ----- Original Message ----- 
  From: paul 
  To: greenkeys at mailman.qth.net 
  Sent: Friday, December 20, 2013 12:56 PM
  Subject: [GreenKeys] inexpensive loop supply transformer wanted


  I'm working on a small project to have a Single Board Computer such as a Raspberry Pi or Arduino drive my TTYs (Model 15 at 45 WPM and a 28 RO at 75 WPM) with some canned messages from memory.  As part of that effort I'd it to have it's own loop supply (120VAC to 120VAC isolation transformer, bridge rectifier, filter cap, 2800 ohm 20 watt limiting resistor).  Does anyone have suggestions on where I might find a low cost isolation transformer for this purpose?


  Paul Newland, ad7i



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