Last updated: 15 June 2003

Autostar Power From Batteries

Sent:	Tuesday, June 10, 2003 07:34:16
From: (Don Sutherland)
Thanks for the great website! In spite of everything I learned from your
site, I went ahead and bought an ETX-105 anyway. I have been planning to
buy a telescope for a few years. I tried different scopes and did a lot
of research before I decided on the ETX-105. I have now found out
firsthand about Meade's manuals. They seem to be fairly complete, but
the critical details don't seem to jump out at you like they should.
With the Autostar, you have to jump between two manuals.

So, rather than wade through the manuals, I played with the Autostar,
but the problem was, dragging the telescope around with me. I found a
power supply for the Autostar on your website, but it seemed to be more
complicated than it needed to be.

I did some tests with the Autostar hand box and I found that the
Autostar runs fine with as little as 5 volts. Below 5 volts the display
starts to dim. Below 4 volts the display is not legible and below 3
volts the microprocessor stops running. I run my hand box using old
9-volt batteries from my smoke detectors, but anything supplying between
4.5 and 12 volts will work. All you need is a cable from the Autostar to
the battery. The Autostar cable uses RJ45 connectors, which are readily
available but a special crimper is needed, so it is easier to buy a
cable with this connector on it. These cables are used for computer
networking and they are available in various lengths at Radio Shack or
any computer store.

Cut the cable about 2 feet from the connector. Trim back the casing a
few inches and cut off all but the brown wire and the orange wire with
the white stripe. The brown wire goes to the positive battery terminal
and the orange and white-striped wire goes to the negative terminal. If
you are nervous about frying your Autostar and want to be absolutely
sure about your connections, turn on the ETX and then unplug the cord
from the Autostar hand box and measure the polarity of the two outside
contacts on the connector. Wire the RJ45 cable to your battery so that
the power supply polarity is the same as on the hand box end of the
Autostar cable. I used the connector from a used 9-volt battery to keep
me from getting the polarity wrong. Some sort of polarized connector
would be a good idea. A rubber band will hold the cable to the battery
and act as a strain relief.

A 9-volt alkaline battery has a capacity of about 150 mAhr. The Autostar
draws 85 mA at full brightness and about 40 mA with the display
intensity turned down, so a battery should last for a few hours, which
should be enough time to learn the Autostar menu maze.
For anyone using batteries to power their Autostar, my factory fresh 497
uses an LM2931S 5.0 voltage regulator. This regulator can run with up to
26 volts DC and has reverse polarity protection up to -15 volts DC. I
don't know if other or older model Autostars use this regulator, but if
they do, reverse polarity is not a problem.

Subject:	re: Autostar Power From Batteries
Sent:	Friday, June 13, 2003 09:53:54
From: (Richard Seymour)
In that note, Don cites the new Autostar as having an LM2931S  regulator,
and describes "successful" operation below 5 volts.  I don't
recommend that, especially if you are trying to use rs232.

The older (later 1999) era Autostars used LM317 regulators, which
start to "starve" the Autostar when the supply drops below 7 volts.

Due to a design quirk of the older 494 (and probably 495/497) Autostars,
it is dangerous to try to run the Autostar below 5 volts internally,
you can corrupt a critical internal register in the computer, rendering
it unusable to normal mortals.
(see: )

have fun

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