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Last updated: 26 June 2007
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Last updated: 26 June 2007 |
Sent: Saturday, June 23, 2007 10:09:17 From: Brad Kauffman (bradk@gte.net) I have just purchased an ETX-125PE and see that Meade no longer offers the electronic focuser for it. I wondered if the focus commands still work from a lap top so I stuck a scope on the aux port and tried the commands. I did figure out the pinout for the ports and that they are hooked to the SPI bus. I isoloted the commands for fast and slow focusing in both directions but the one missing link is that the power to the port is not automatically on, it must need a command back from the focuser to turn it on. Do you know if anyone with a meade focuser has identified commands from the focuser? If I could get that I could throw together a focuser for it. Brad
From: richard seymour (rseymour@wolfenet.com) (why does the phrase "hot potato! hot potato!" run through my mind?) >> I have just purchased an ETX-125PE and see that Meade no longer >> offers the electronic focuser for it. I wondered if the focus commands >> still work from a lap top so I stuck a scope on the aux port and tried >> the commands. I did figure out the pinout for the ports >> and that they are hooked to the SPI bus. Strictly speaking, that's not correct. The 68hc11's SPI bus is not attached to anything in the Autostar. The AUX signals are generated by a PIC chip under control of the Autostar. They're just like the motor signals, simply from a different pin set. The clock and data lines are individually toggled by the Autostar itself as PIO pins, rather than using a pre-built SPI system. >> I isoloted the commands for fast and slow focusing in both directions but >> the one missing link is that the power to the port is not >> automatically on, The AUX port is always powered. It's a 4-pin socket, and the outer two are battery and ground. The clock and data lines run through the center two. Full pinouts of everything 497 Autostar-associated are at: http://jan.eaglecreekobservatory.org/pinouts.html >> it must need a command back from the focuser to turn it on. No, it's weirder that that... every second the autostar asks the AUX bus "what's out there?" ... based upon the response (silence, or a chorus of bits) it will offer (or not) the focus menu, and emit focus commands if directed by the serial commands. The AUX (and motor) system is a bidirectional bus carrying address and data packets... the Meade "peripherals" (focuser, 909 APM, LNT, GPS) all have microcomputers (PIC chips) in them, and can engage in a two-way dialog with the Autostar. For focusing, the 909 APM serves as an interface between "motor only" focusers (like a 1206 or 1209) and the Autostar. (but Meade does not "support" the 909 for scopes other than the LXD family or the LX90... but my patch kit overrides that marketing decision). >> Do you know if anyone with a meade focuser has identified >> commands from the focuser? >> If I could get that I could throw together a focuser for it. I'm trying to find my file with that particular set of notes (it was written 3 computers ago, and is buried deep in the pile of "from old computer" files). If/when i find it, i'll send it along. It's the handshake at the beginning which is the puzzle.. once the Autostar knows it's there, it sends a packet with the speed (one of four) and a direction bit. What i -recommend- (for results sooner) is buying any Meade autostar-capable focuser, and using its electronics for whatever design you're planning. have fun --dick
And:
Thanks for the info! I am attaching the traces I got off the aux port. The protocol looks like a simple SMB bus. I am pretty familiar with programming the 68HC11 in assembly language for some other applications so I have seen this kind of bi-directional communications before. The traces were obtained by attaching a scope to the aux port pins while the autostar was connected to a laptop via RS-232. From the control panel for slewing and focusing on the laptop I tried both focus in and focus out at the two speed options. I also noted that the stop command in the traces is sent when you let off the focus. Looks like each command sent is 4 bytes. The first byte is usually the address of the device on the bus. Of the 4 wires in the aux port it was clear that 3 of the wires are the data, clock, and ground. The forth seamed to be floating at around 1 volt which I presume would be power if it was turned on. If you do find any other data it would be great. Otherwise buying a focuser and using the electronics is probably the best idea as you said.Brad
And:
Brad Kauffman wrote: > Thanks for the info! I am attaching the traces I got off the aux port. The > protocol looks like a simple SMB bus. It's a "modified IIC (or I2C) bus"... they don't use the 9th bit (nor the final response, if i remember correctly) that the true IIC bus standard dictates. > I am pretty familiar with programming > the 68HC11 in assembly language for some other applications so I have seen > this kind of bi-directional communications before. The traces were obtained > by attaching a scope to the aux port pins while the autostar was connected > to a laptop via RS-232. From the control panel for slewing and focusing on > the laptop I tried both focus in and focus out at the two speed options. When run from the keypad, you have four speed options. > I also noted that the stop command in the traces is sent when you let off the > focus. Looks like each command sent is 4 bytes. The first byte is usually > the address of the device on the bus. Of the 4 wires in the aux port it was > clear that 3 of the wires are the data, clock, and ground. The forth seamed > to be floating at around 1 volt which I presume would be power if it was > turned on. If you do find any other data it would be great. Otherwise buying > a focuser and using the electronics is probably the best idea as you said. The power -should- be always on, if the telescope is powered. Refer to any number of diagrams of the ETX or LX90 power panel (such as http://jan.eaglecreekobservatory.org/powerpanel.html ) If you're not seeing power on the 4th pin, your power panel probably has a blown trace. I'm still digging for the old documents... have fun --dick
oops. I checked again and I had that channel on the o-scope on 1X instead of 10X so it was reading 1.2V instead of 12V. There is power to pin 4. Now I can easily make a motor drive that uses the commands I recorded. I will be able to focus from the laptop screen but I would still need the signal to turn on the autostar signal if I want to focus with the autostar. Thanks again. Brad
And:
Brad Kauffman wrote: > oops. I checked again and I had that channel on the o-scope on 1X instead of > 10X so it was reading 1.2V instead of 12V. There is power to pin 4. It's amazing what an unnoticed 10x switch can do... > Now I > can easily make a motor drive that uses the commands I recorded. I will be > able to focus from the laptop screen but I would still need the signal to > turn on the autostar signal if I want to focus with the autostar. Ooookay... one reference i forgot to cite is Meade's patent on the Autostar messaging and protocols: 6,304,376 which you can access at: http://patft.uspto.gov/netahtml/PTO/srchnum.htm (also 6,392,799 6,445,498 6,563,636 align: 6,922,283 ) I've exhumed some of the files i was seeking (dated early 2001). Much of the work is from Stefan Keller-Tuberg's signal analysis. The AUX bus shows the following bytes being carried: AUX: 0x2 0x1 00 (3 bytes total) AUX: 0x1 00 (2 bytes total) AUX: 0x3 0x1 0x1 0x81 (4 bytes total) AUX: 00 (1 byte total) AUX: 0x3 0x1 0x1 0x82 (4 bytes total) AUX: 00 (1 byte total) AUX: 0x3 0x1 0x1 0x83 (4 bytes total) AUX: 00 (1 byte total) AUX: 0x3 0x1 0x1 0x84 (4 bytes total) AUX: 00 (1 byte total) (the following are from a different analysis system) AUX decoded: 0x2 0x1 00 (3 bytes total) (1 times) AUX decoded: 0xff (1 byte total) (1 times) AUX decoded: 00 (1 byte total) (33 times) AUX decoded: 0x1 (1 byte total) (1 times) AUX decoded: 0x3 0x1 0x1 00 (4 bytes total) (6 times) AUX decoded: 0x3 0x1 0x1 0x1 (4 bytes total) (3 times) AUX decoded: 0x3 0x1 0x1 0x2 (4 bytes total) (3 times) AUX decoded: 0x3 0x1 0x1 0x3 (4 bytes total) (3 times) AUX decoded: 0x3 0x1 0x1 0x4 (4 bytes total) (3 times) AUX decoded: 0x3 0x1 0x1 0x81 (4 bytes total) (4 times) AUX decoded: 0x3 0x1 0x1 0x82 (4 bytes total) (4 times) AUX decoded: 0x3 0x1 0x1 0x83 (4 bytes total) (4 times) AUX decoded: 0x3 0x1 0x1 0x84 (4 bytes total) (4 times) Looking at the first group, the AUX: 0x2 0x1 00 (3 bytes total) is the Autostar's query, and the AUX: 0x1 00 (2 bytes total) is probably the focuser's response. The rest of the lines (without the word 'decoded') are the Autostar commanding the various speeds, and (i think) the focuser replying. He also created a minimal "logic analyzer" monitoring the clock and data lines by strobing his parallel port. That yielded data such as: -------------- Symbol period: 17792 microseconds Number of bit changes in sequence: 66 Changed bits: AUX_CLK(08) AUX_DAT(80) 88 00 08 00 08 00 08 00 08 00 08 00 08 80 88 80 88 00 08 00 08 00 08 00 08 00 08 00 08 00 08 80 88 00 08 00 08 00 08 00 08 00 08 00 08 00 08 80 88 80 88 00 08 00 08 00 08 00 08 00 08 00 08 80 88 08 AUX decode (4 bytes): 0x3 0x1 0x1 0x81 AUX_CLK: 101010101010101010101010101010101010101010101010101010101010101011 AUX_DAT: 100000000000011110000000000000011000000000000001111000000000000110 ----------------------------- Andrew Johansen has done similar studies, but he was concentrating on the motor card signals in an LX200gps, not the focuser. At the moment i can't locate his logic analyzer traces, but they're not focus related. so that's a start... run with it and please keep us posted have fun --dick
And:
Thanks for all the data. This is matching what I am getting too. I have captured the query from the autostar so far and the response from the clock in the LNT module. Haven't worried about what the clock is sending yet. I have an 8051 based board I am going to hook into the aux port so I can experiment with send and receive on the data bus. Brad
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