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This page has been rewritten a few times, resulting in some
redundancy.
You can ignore most of the first two paragraphs (mostly a screed).
I have a whole photo album full of excellent deep-sky photos taken with this set-up...and some year I'll have time to scan them and post them in a gallery. In the meantime you'll have to be satisfied with a few samples that demonstrate how well the guiding works.
I recently found Mike Marshak's website where he claims to be able to do this without the 520 electronic relay. The setup is similar. I thought that might be possible but didn't want to take a chance on wrecking the 201 (you have to wire straight to the autoguider in his version). Here's his modifications page.
See also my page showing various simple improvements
and fixes for the LX10.
Questions or comments? Email me at jmmahony@hotmail.com
I'm a fairly experienced astrophotographer on a rather limited budget. And although I'm too young to be a grouchy old man in most respects, I've been involved in amateur astronomy long enough to have developed a bit of an old fart's attitude when it comes to some modern hi-tech astronomy equipment. First, I have no interest in paying lots of money for a modern computerized go-to system. I have so much experience using telescopes that I can frequently find objects faster with my simple clock-driven manually operated scope than other people can using computerized go-to systems. For that matter I like the learning of the sky and the enjoyment of the occasional accidental "discovery" that comes with using the old methods of star-hopping and using a good star-atlas. Another way I'm old-fasioned is that I prefer film-based astrophotography over CCD photography. I prefer film partly because of its larger field of view, partly because taking a 3-color CCD image often requires nearly as much total exposure time as film, with quite a bit of extra fiddling (flat frames, dark frames, changing filters, etc.) to boot, and partly because of the expense of good CCD equipment. There is a drawback with film, in that guiding is more important (because of the longer exposure time) and more difficult (for example, there's no automatic "track and accumulate" mode). With film you rely on old-fashioned off-axis guiding. It is possible to do this manually, but for most exposures that's true only if you have the patience of a saint. For the rest of us, the modern autoguider is a godsend. But here's where a problem comes up if you have a simple scope. Meade autoguiders today are designed to be plugged straight into a modern computerized go-to scope. Meade sells a converter (Electronic Relay, part #520) to convert the Meade autoguider signals to simple on-off signals for each of the four directions of motion, but this works directly only on very simple and straightforward motorized drive systems. Such drive systems were common until a decade or two ago, but today they exist primarily only on a few older and/or homemade mounts. Digital technology and stepper motors have changed everything. And commercially available scopes are now cheap enough and good enough to make building your own mount a questionable idea. So what do you do if you have (or want) a cheap, simple scope, but want to use an autoguider to make taking great pictures easy? The rest of this article explains how to connect a Meade autoguider to the LX10 Schmidt-Cassegrain.
The LX10 is an excellent basic low-cost clock-driven scope, with an inexpensive dual-axis (guiding-speed only) control system available as an option. Meade's catalog says their Electronic Relay can be used to connect a Meade autoguider to any telescope with a dual-axis drive corrector system, but if you ask their customer service representatives about using it on an LX10, they'll say it can't be done. That's partly because their customer service representatives (for their simpler scopes, at least) are technical nincompoops (they're hired more to be salesmen, after all, and there are a few complications-the electronic relay won't do it alone, which is the whole point of this article), but they probably say it can't be done mostly because they don't want to deal with any legal liabilities if they tell people how to do it and someone tries and damages their scope or autoguider in the process. In that spirit I should tell you first that my experience in electronics is rather limited, and second, that the schematic diagram of the circuit board of the LX10's drive system is based on an old sketch I made when I connected mine to a Meade 201 autoguider a few years ago. At the time I made the mistake of using a pen to draw the original sketch of the connections on the circuit board, and by the time I revised the diagram enough to make sense of what was really happening, there were many scratched out lines, and I never made a cleared-up final version. So when I tried to make sense of it again for this page (a few years later), my memory had faded and I wasn't quite sure if I was reading all the details correctly. Fortunately the general ideas are right, and even better, you don't even need to make sense of it to connect your scope to the electronic relay-you can just follow the directions for making the connections-the details of that part I am more certain are correct. I only included the schematic if you want to understand what was happening. But the point is, use this info at your own risk.
The basic idea is to duplicate the actions of the switches in the handbox using the switches in the Electronic Relay (one for each directions). So you will need a six-conductor phone plug and some wire to connect the scope (through the handbox socket) to the Electronic Relay (or SBIG unit). With most SBIG units, this can be done rather directly, and although the output of the Electronic Relay originally appears identical to SBIG's output, there are a few complications due to some limitations of the solid state switches in the Electronic Relay. For one thing, although there are three outputs for each (direction) switch on the relay, (labelled common, normally open and normally closed, as in a standard double-throw switch), Meade's instructions say that for each set of three outputs, you can use the common and either the n.o. or n.c. contacts, but not both (i.e., you get a single-throw switch, not a double-throw). Here's where the main complication comes up-the handbox switches for the declination (north or south) directions are double-throw switches that are needed to reverse the polarity to the declination motor. The answer is simple, in theory: just use the Electronic Relay switch to run a conventional electro-mechanical double-throw relay. You will have to be very careful about the current needed to run the standard relay (the "coil current") as the switches in the Electronic Relay are limited to 100 ma, which is pretty small to run a standard relay. I used a relay from Radio Shack whose coil is rated at 90 ma @ 5V, which is the voltage that they will be used at. There's one other detail you should be aware of- Meade says that for each direction, of the two connections you make (to "common" and either n.o. or n.c), the lower voltage must be attached to the "common" pin. This simply means you need to be careful which way you wire things. Also there's a minor glitch that sometimes comes up in the "east" direction control, again due to the low current restriction for the switches in the electronic relay. There's a simple fix for that (mentioned below), but again the problem is so rare I haven't bothered to fix it.
Note: For those with even less experience with
electronics
than me, there are explanations for various basic terms and symbols at
the bottom of this page.
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Warning: There is some inaccurate information in Meade's autoguider instructions reguarding the connection between the Autoguider and the Electronic Relay. Make sure you follow the instructions that come with the Relay itself to make that connection.
The first thing to realize about the schematic is that the circuitry occurs in three stages. The first is just the power source (batteries (6 or 9V) or a 12V external source), along with what I assume is a voltage regulator (Q1). Given my limited knowledge of electronics, I only recently became aware that small, transistor-sized regulators were available. I labeled it Q1 only because it looks like a transistor, and I don't know what symbol or letter to use for a voltage regulator. The voltage coming out of Q1 (measured at 5V on my scope) is what actually runs everything on the scope.
The second stage is, I think, just another ("second stage") voltage regulator (along with the power-on indicator LED, a minor detail). This makes sense because the first stage has to deal with an input of either 6, 9, or 12 volts, depending on what power source you use, so its output would probably not be regulated well enough for a telescope R.A. drive. Thus the second stage is needed to refine the first. BTW the first stage is useful if you have an older LX10 where the 4 AA sized batteries have to be installed by removing the bottom plate of the scope. Since the internal and external power sources are wired identically, you can just put the appropriate plug on the 6V battery pack and plug it in through the front panel external power socket, even though that socket is labelled 12V (note: center pin positive).
The third stage is where the real action happens. Q3 is (I think) a real transistor. It supplies the standard sidereal rate tracking voltage (about 3V) to the R.A. motor. (Note- the variable resistor in the diagram, accessible through the bottom plate, can be used to adjust the voltage to the transistor base, hence fine-tuning the drive rate. This detail is not mentioned in the manual.) When you use the handbox, the east button has the effect of shorting out the transistor base, hence shutting down the transistor and the R.A. motor (the LX10 uses a standard 2X sidereal guiding rate, which really means normal sidereal rate +/- 1X sidereal for west or east, so east is 0X sidereal, i.e., the motor is stopped). There is a bit of awkwardness here: when you do this, you're draining wasted power by shorting the power supply from Q2 through (part of) the variable resistor (I haven't found a better solution myself, short of using a connection more complicated than the standard 6-conductor phone plug connection through the handbox socket.) This is the source of one minor problem in my set-up: If the weather is cold and the grease in the drive gears thickens or the batteries weaken, I have to turn the variable resistor up to near maximum, and then when the autoguider sends an east signal there can be too much current going through the solid-state electronic relay switch (it's limited to 100 ma) so sometimes the east direction doesn't work right. This only happens when it's very cold (in fact on moderately cool evenings it makes a useful test of whether I've got the speed set too high!) You can correct this if you want by using the electronic relay to run a standard relay (as in the dec controls), and then use that relay to control the "east" direction. Check Meade's instructions for the electronic relay before making any changes to my design, though, because there's one other important detail-for each direction/switch the "common" lead for that direction has to be connected to the scope lead (of the corresponding direction) of the lowest voltage potential (ground, in this case).
For the west direction, the handbox switch simply connects the R.A. motor directly to the 5V output from Q1. This is more than the 3V the motor normally gets from Q3, so the motor speeds up. This connection is converted directly to electronic relay control.
Declination: this is pretty simple: the handbox switch sends the 5V output of Q1 to the Dec motor. But here's where the extra work comes in. The handbox does this using double-throw switches to reverse the polarity, but the switches of the electronic relay can be used only in normally-open or normally-closed mode, not both at once, so you need to use the electronic relay to run standard double-throw relays, and then use those to run the Dec motor. You need to be careful in your choice of relays since the electronic relay switches are limited to 100 ma. Mine are tiny relays rated at 90 ma @5V. These were the smallest, lowest coil current relays I could find at Radio Shack.
Various semi-important details: the colors mentioned in the wiring diagram refer to the colors of the 6 wires in the cord from the handbox to the scope. The cord that comes with the autoguider has the same colors, but reversed, and with a different ordering for the direction wires. Also if you look close, you'll notice the cord has the blue wire (corresponding to the white power line in my diagram) cut at the ends. This is because the autoguider and the telescope each have their own power supply, so you only need the directional and ground connections. But the electronic relay doesn't have its own power supply, so it comes with its own cord, without the cut line, and Meade's instructions for the relay point out that you have to use that cord for the autoguider-relay connection, not the cord that comes with the autoguider. The connection you need to make is between the electronic relay and the scope using the (hand-box) phone socket on the scope and the 15-pin plug on the electronic relay (a smaller version of a standard 25-pin computer parallel port plug). The numbers (and the corresponding drawing) in the diagram refer to the pins on male plug on the electronic relay, not the female-socket-ended cord that comes with it. You'll need a 6-lead phone plug and some wire. The electronic relay comes with a 15 pin socket and attached cord. You just need to make the connections between the phone plug and the 15 pin socket cord (note again the forth part of the diagram refers to the male plug on the relay, not the female socket on the included cord! Make sure you get the pin numbering correct!), with two extra double-throw standard relays between, as diagramed above.
One more useful detail: The
variable
resistor that controls the R.A. speed is 500 ohm (linear taper).
I found that I only used 200 ohms of that at one end (the higher
potential
end) of the resistor's range, so I replaced it with a 300 ohm fixed
resistor
and a 200 ohm variable, which I mounted on the front control
panel.
This gives me a good fine speed control. (The extra resistor I
added
is not the one shown in series with the variable resistor in the
diagram,
that's already there on the circuit board.)
Electrical Terms and Symbols:
The terms "double-throw" (DT), "normally open" (n.o.), and "normally closed" (n.c.) and "common" are used to describe various aspects of switches. Many spring-loaded switches, such as some pushbutton switches (or the keys on a computer keyboard) have a "normal" unpushed ("unswitched") position (as opposed to the pushed "switched" position) in which the switch is (usually) "open", meaning no electricity can flow through. When the switch is "switched" (pushed, or otherwise activated), the switch is (usually) "closed", meaning electricity goes through. This type of switch is called "normally open". Ocassionally the situation is reversed and the switch allows electricity through unless it is "switched". This type is called "normally closed".
The term "double throw" refers to a type of switch that has two switch positions, but it's not just a simple on/off switch. Instead, there are three wires connected to it. One of these is the "common" lead (frequently connected to a voltage source), and the other two wires connect to two other things. Electricity goes from the "common" wire to one of the other two wires, depending on which position the switch is in. These can also be spring-loaded, with an unpushed ("normal") position and a pushed ("switched") position. The switches in the handbox are of this type. ( A simple on/off switch can be described as a "single throw" switch).
When searching for relays, you'll usually see an abbreviation like "SPST" or SPDT" or "DPST" or "DPDT". The third and fourth letters ST or DT refer to single-throw or double-throw. You'll need DT. The first two letters SP or DP stand for single-pole or double-pole. Here "pole" is a synonym for "switch" so DP just means a relay with two switches controlled simultaneously by one electromagnet. You can use these (as long as they're double throw)-just ignore one set of switch connections on each relay. If you see the terms "normally open" (or n.o.) or "normally closed (n.c.), don't use these: only single-throw switches can be n.o. or n.c., and you need double-throw
The "handbox" section of the above diagram shows the symbols for the four direction switches in the handbox. All are spring-loaded double-throw switches shown in the "normal' (unpushed) position. For example, the north switch "normally" allows electricity to flow from the R (red) wire to the W (white) wire, but if pushed, those wires become disconnected and electricity flows from the R wire to the Bk (black) wire. Note that the east and west switches have no wire connected to the "normal" position, so these switches are actually being used as simpler "single-throw, normally open" on/off type switches.
A "relay" is, in general, a device that allows you to operate a switch in one circuit from some other circuit. Meade's Electronic Relay is a fancy version that is actually four relays, one for each direction. But first, I will describe the simple standard relays you will need to make the connection between the Electronic Relay and the scope. The connection between the "controlling" circuit and the switch in the "affected" circuit (my own terminology) is usually not electrical so that there is no way for the circuits to interfere with each other in an unintended way. The simplest way to do this is to attach a piece of iron to the switch and use an electro-magnet operated by the "controlling circuit" to physically control the position of the switch. (In this "electro-mechanical" type relay, the switch is generally spring loaded and usually of the "double throw" type). There are other types of relays available, but the others I've seen are all single-throw types, and we need double-throw. Electro-mechanical double-throw relays are widely available from Radio Shack and other suppliers for a few dollars each. You'll need two. And be careful about the current needed to operate the electro-magnet (usually referred to as the "coil current"). These will be operated by the Electronic Relay, and the switches in the electronic relay have a limit of 100 ma, which is pretty small to run a standard relay. If you're wondering why we need to use one relay to operate another, it's because the handbox operates the declination motor with double-throw switches (needed to reverse the polarity to the dec motor), and the switches in the electronic relay, although they have three connections for each direction, are solid-state switches that can only be used as single throw switches (either normally on or normally off, but not both simultaneously, ie, you can use only the common and one other connection, for each direction). The symbols for the two standard relays are shown in the third part of the above diagram. The top part of each symbol shows a double-throw switch, and the lower part that looks like a string of bumps represents the coil of wire that makes the electromagnet that controls the switch. So (in the first symbol) when a current flows through the magnet connected between the W (white) wire and the #13 wire, the switch gets pulled down, which breaks the connection between the "common" R (red) wire and the "normally closed" W (white) wire and makes a connection between the R wire and the "normally open" Bk (black) wire.
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