[GreenKeys] Loop supplies

[Steve Garrison]

I'll be using John's ttyloopdriver at my hamfest demo this weekend doing the TTY Texting.  With his older design in attendance as a backup.  Both devices work as advertised.

As for difficulty of assembly, I had 3 of the smallest SMD devices soldered in place by a professional (she is a ham as well) and did the rest of the board myself.  The biggest drawback for some would be cost.  Sourcing such small quantities of components from DigiKey, Mouser, and CoilCraft doesn't offer much in the way of discounts.  I thing it was close to $130.00 when all was said and done.  But IMHO, well worth it for a very small and professional looking solution.

Thanks for all your efforts John.

Steve G./N4TTY
Sent from my iPhone

On Oct 31, 2018, at 4:59 PM, John Nagle <nagle at animats.com> wrote:

>> On Behalf Of W9DDD > Sent: Monday, October 29, 2018 1:59 PM
>> Subject: [GreenKeys] Loop supplies or selector magnet drivers
>> Wonder what people are using these days loop supplies and keying the
>> loop or selector magnet directly.  I was thinking of going old school
>> with 120 VDC and a series 2,000 ohm 10 watt resistor. But, looking at
>> the prices for 10 watt resistors, I'm re-thinking things.
>> I might get lucky with something already being in the LESU of the
>> pending 28, but I'm not counting on it.  I'm trying to get setup so all
>> I have to do is plug it in when the 28 arrives.
> 
>    I've been down this road several times, as many of you know.
> 
>    First I did a more or less traditional setup, with a 120VDC supply
> and a 2K 10W resistor.
> 
>   http://www.aetherltd.com/connecting.html
> 
> These work fine. I've had two of them in use for almost a decade.
> The 2K 10W resistor used is a strange thick-film device which can
> be mounted on a PC board without scorching it, because it has so
> much surface area.
> 
>    Then, as a technical tour de force, I built a 120V 60mA
> driver for Model 14 and 15 Teletypes which is powered entirely
> from a USB port.
> 
>   https://github.com/John-Nagle/ttyloopdriver
> 
> It's the size of a cigarette pack and generates little heat.
> It uses a custom-designed special purpose switching power
> supply. No energy wasted in a big resistor.
> 
> It's the ultimate solution to driving an old Teletype from
> a computer. But it's hard for homebrewers to build.
> It's all surface mount.  It has to be, or the switcher
> wouldn't work. It's designed like a modern
> production product, with protection circuitry and startup
> power management.  This is how you'd do it if you were
> having a thousand built in Shenzhen. But it's beyond most hams.
> Steve Garrison has built some from this design.  I've built some.
> But the market is too small for this to be a product.
> 
>            John Nagle
> 
> 
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