[simpits-tech] Driving Synchros - Here is what I found...

[Erwin Neyt]

Gene, Marv,

I found this Air Core Driver, it produces the needed SIN/COS signals. 

In your previous post you said, I quote:

"The two electromagnets are fed voltages that are 
multiplied by the  sine and the cosine of the desired angle which you 
want the needle to point.  If you feed the two electromagnets AC signals 
that are 90 degrees out of phase the needle will spin, completing one 
revolution for each cycle of AC."

That excactly what the Philips SA5775 does.

>From the spec sheet:
The SA5775A is a monolithic driver for controlling air-core (or
differential) meters typically used in automotive instrument cluster
applications. The circuit interfaces with a microprocessor through a serial
bus and directly drives the air-core meter. The SA5775A has 10-bit
resolution (0.35 degree) and is guaranteed to be monotonic. Data can be
shifted through the part, allowing several SA5775As to be cascaded with only
one chip-select line. On-chip current shut down logic protects the circuit
from external faults. 

Take a look at the application note I included. Other similar products are
the SA5777 and the SA5778. More info on
http://www.semiconductors.philips.com/ (search on the part numbers and
follow the links to additional info)

The good thing is that these chips sell for <$10

Let me know how this looks to you guys,

Erwin.

> -----Original Message-----
> From: Marv De Beque [mailto:debequem@speakeasy.net] 
> Sent: vrijdag 5 april 2002 13:43
> To: simpits-tech@simpits.org
> Subject: Re: [simpits-tech] Driving Synchros - Here is what I found...
> 
> 
> Gene,
> 
> The resolver you handed me has 6 wires.  The synchro receiver has 5 
> wires.  I think the synchro receiver is some sort of a 
> hybrid.  Do you 
> have data sheets?
> 
> Marv
> 
> 
> On Thursday, April 4, 2002, at 11:09 PM, Gene Buckle wrote:
> 
> >> However, I do have another proposal.  I believe I can 
> build a small 
> >> microprocessor based board that will accept a serial data 
> input with 
> >> 12 bits of precision that will produce two 12 bit precision analog 
> >> outputs designed to drive a single 4-wire synchro.
> >>
> > You sure they're only 4 wire?  How many wires did that one 
> I gave you
> > have
> > on it?  I don't recall.
> >
> >> About 0.18 degrees of resolution.  That is, 12 bits minus 1 bit of
> >> noise
> >> for 11 bits or 2^11 which is 2048.  If you divide 360 by 
> 2048 you get
> >> 0.1758 degrees.  I think that amount of movement is fine 
> enough for us
> >> regular guys and girls.
> >>
> > 10 bits would work as well.  That should give you 1024 positions.
> >
> >> The other issue is latency.  There will be a small amount of time 
> >> between when the digital number is received and when the value is 
> >> translated to the synchro.  I would expect that latency to 
> be under 
> >> 10 milliseconds.  I think that is plenty quick enough for us.
> >>
> > 10ms is fine.  150ms is the high end limit for a Class D FTD.
> >
> >> micro.  Each board could be "strapped" with an address 
> using jumpers 
> >> so you can assign a unique place in the data string to 
> grab its data.
> >>
> > I2C or SPI/Microwire would work well here.
> >
> > g.
> >
> >
> >
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