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Discussion Groups | BasicX | Re: Re: Power through slip rings
Discussion forum for the BasicX family of microcontroller chips.
Re: Re: Power through slip rings - Rich - Mar 18 14:38:33 2007
I have had great success with inductive coupling. Slip rings are an old fashioned method
that is not practical in most of the demanding requirements today.
----- Original Message -----
From: Tom Becker
To: b...@yahoogroups.com
Sent: Sunday, March 18, 2007 1:35 PM
Subject: [BasicX] Re: Power through slip rings
FYI, a year ago I asked here about using slip rings and rotary
transformers - specifically video head drum assemblies - to power a
rotating project. I've returned to this again after a year of
essentially-continuous project rotation.
The summary is pretty simple:
- Slip rings are a poor choice unless the project can support sealed
mercury-wetted contacts - which are expensive; otherwise, physical
wear was high and electrical noise was eventually unforgiving.
- The rotary transformers in video head drums cannot convert
sufficient energy to make them useful for significant project power,
but read on.
Using paralleled high-drive 74AC14s in push-pull as an H-Bridge to
switch (at 24MHz!) two paralleled fixed coils, and stacking the
corresponding rotating secondary coils then rectifying and smoothing,
the best I was able to achieve was 5vDC @10mA, unregulated. That
might be sufficient for some low-current functions like analog
preamplification or some processing on a small PIC board, but it is
not enough to run a Basic-X or similar processor with any significant
peripherals.
However, I learned good news. Getting digital data on and off
a rotating platform via the coils is very easy, and it is very fast -
much faster than any radio solution.
Driving one side requires only a fast buffer or inverter (I'm using
74AC14s but a 74HC14 is fine) through 200 ohms to a transformer coil
to 0v. On the receiving side, the hysteresis of a 74HC14
Schmitt-trigger inverter reconstructs the logic levels of the driven
side after adding the transformer output to a mid-logic bias from a
pair of series 10k resistors from Vcc to 0v. The transformer
secondary is connected between Vcc/2 and the Schmitt input; if the
resulting sense is wrong, reverse the transformer secondary coil.
That's all there is to it; depending on the video drum assembly,
you'll have two, four, six or eight bidirectional channels - probably
in pairs because each pair might share a common on one side.
I was able to move TTL digital data (I tried 19200 TTL serial, a 10MHz
modulator stream and a 30MHz clock simultaneously) through this link
with only a ~30nS delay. Few things are as simple and work so well.
Now then, power remains a problem...
Tom
[Non-text portions of this message have been removed]
(You need to be a member of basicx -- send a blank email to basicx-subscribe@yahoogroups.com )
----- Original Message -----
From: Tom Becker
To: b...@yahoogroups.com
Sent: Sunday, March 18, 2007 1:35 PM
Subject: [BasicX] Re: Power through slip rings
FYI, a year ago I asked here about using slip rings and rotary
transformers - specifically video head drum assemblies - to power a
rotating project. I've returned to this again after a year of
essentially-continuous project rotation.
The summary is pretty simple:
- Slip rings are a poor choice unless the project can support sealed
mercury-wetted contacts - which are expensive; otherwise, physical
wear was high and electrical noise was eventually unforgiving.
- The rotary transformers in video head drums cannot convert
sufficient energy to make them useful for significant project power,
but read on.
Using paralleled high-drive 74AC14s in push-pull as an H-Bridge to
switch (at 24MHz!) two paralleled fixed coils, and stacking the
corresponding rotating secondary coils then rectifying and smoothing,
the best I was able to achieve was 5vDC @10mA, unregulated. That
might be sufficient for some low-current functions like analog
preamplification or some processing on a small PIC board, but it is
not enough to run a Basic-X or similar processor with any significant
peripherals.
However, I learned good news. Getting digital data on and off
a rotating platform via the coils is very easy, and it is very fast -
much faster than any radio solution.
Driving one side requires only a fast buffer or inverter (I'm using
74AC14s but a 74HC14 is fine) through 200 ohms to a transformer coil
to 0v. On the receiving side, the hysteresis of a 74HC14
Schmitt-trigger inverter reconstructs the logic levels of the driven
side after adding the transformer output to a mid-logic bias from a
pair of series 10k resistors from Vcc to 0v. The transformer
secondary is connected between Vcc/2 and the Schmitt input; if the
resulting sense is wrong, reverse the transformer secondary coil.
That's all there is to it; depending on the video drum assembly,
you'll have two, four, six or eight bidirectional channels - probably
in pairs because each pair might share a common on one side.
I was able to move TTL digital data (I tried 19200 TTL serial, a 10MHz
modulator stream and a 30MHz clock simultaneously) through this link
with only a ~30nS delay. Few things are as simple and work so well.
Now then, power remains a problem...
Tom
[Non-text portions of this message have been removed]
(You need to be a member of basicx -- send a blank email to basicx-subscribe@yahoogroups.com )