[GreenKeys] New 60ma current loop driver board design

[John Nagle]

On 10/29/2016 01:49 AM, Alf Fisher wrote:
> Hi John,
> Could the same principles be applied to driving British double current
> machines where the current is 20mA and the magnet is stable in both mark
> and space states and only needing a kick to flip it over.  Circuitry
> could be tricky getting the dual polarity.
> The resistance and inductance of each coil being 363 ohms and 4 - 4.5
> Henries  each and are connected in series.
>
> Alf
> G3WSD

      It's possible, but would take a different design.
This design uses the SPACE time to charge up a capacitor,
and uses the charging supply to provide the sustain current
after pulling in the selector magnet.  For an always-on
polarity-reversing system, there are several things that
could work.  One is a separate sustain supply, and an
H-bridge to reverse the output polarity.  Or just
two copies of the existing design with opposite
polarity and some logic to coordinate them.

				John Nagle