corsechris Posted August 16, 2005 Posted August 16, 2005 Steve, OK, looked at the chip data sheet (mmmm...data sheet....) and I suspect it may not actually help you much. It's quite likely that the PDA has the same or very similar device in it's output stage already. You can give the potting-down method a go if you like, but it would probably pay to get an oscilloscope on it and see whats going on. It definately expects TTL inputs but is getting probably +- 6 or 7 volts from the PDA. Are you into electronics DIY?? If so, I'll do a quick circuit you can try. Main thing seems to be getting a proper voltage swing on it. The convertor you have only makes about +- 7v with little drive capability behind it. A line driver tacked on the end of the PDA might work but you'll need a proper set of voltage rails. It's also vaguely possible that the 'scope is trying to pull some volts out of the serial port but not really that likely. Where abouts are you?? I'll bring my sillyscope and we can compare notes Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 It appears that if the last two bits are 01 they both need removing and if the last bit is a 0 only that needs removing. Don't know what this proves, but it has been good fun working it out Mel, I love all this (no really!. The transformation is very interesting but there is NO 'intelligence' or processing capability in this device, it is purely a chip with a voltage double, voltage inverter and switching to turn TTL levels into true RS232 levels (+-12v nominally) so although we have both found patterns, it is hard to see how a voltage level converter can possibly make a data transposition! The really sad part is that I have now spent three long evenings on it Having now taken my 'passive' breakout box out of the loop, I have actually got the PDA to drive the telescope directly thus obviating the need for this bl**dy device ( I must assume that the LEDs in the breakout box were drawing sufficient current to kill the low voltage output of the PDA ). Sadly, I originally needed the breakout box in line to allow me to determine the connections required .... Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 The RS232 connections are not direct ie pin 2 to pin 2 in a null modem cable, they are all mixed up....dunno if it's any help Cheers Mark, I have been using a breakout box to get the connections right and they are right but the box has added problems of it's own! Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 I think i'll be looking at my Dad's telescope in a different light from now onwards You're supposed to look *through* them, not at them, and generally in the dark... You know what, I should be looking through mine and not fart a**ing around with the electronics - it was a clear sky last night and I was soldering not viewing Quote
melf Posted August 16, 2005 Posted August 16, 2005 Hi Steve Did you get the mail re setting parity and stop bits etc If information is getting through - which from reading the thread it appears to be, then I would suggest that it points to a protocol setting not a physical electrical problem Melf (not melt - is it sad that we both have views on this ) Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 Are you into electronics DIY?? If so, I'll do a quick circuit you can try. Main thing seems to be getting a proper voltage swing on it. The convertor you have only makes about +- 7v with little drive capability behind it. A line driver tacked on the end of the PDA might work but you'll need a proper set of voltage rails. It's also vaguely possible that the 'scope is trying to pull some volts out of the serial port but not really that likely. Chris, I got the oscilloscope out last night to check the voltage levels prior to adding the resistors. I have a very nice 0v-5v pulse indicating that the levels are CMOS not TTL and the device requires TTL input. With this in mind, I put a range or variable resistors in line and only got a result when using a 220K pot in series, ( I didn't try potting to ground ). However, the result was that I got the same incorrect data right up to the point where the resistance was such that it died on me completely and no data appeared at the output! I also tried another experiment:- I have two of these devices as I am also trying to interface a friend's telescope in the same manner. I connected the two devices back to back, i.e. with the TTL connections joined ( but data line crossed of course ), connected the PDA to one RS232 port and the telescope to the other - it worked perfectly. I determined therefore that if it could drive this device it should be able to drive the RS232 port on the telescope directly ( even though it ha resolutely failed to do so before! ). This time, I took the breakout box out of the line as it had already served it's purpose in determining the correct Tx/Rx connections and lo and behold, the bl**dy PDA drives the telescope directly. As noted in an earlier reply, I suggest that the LEDs in my 'passive' breakout box were draining the data levels sufficiently to kill the signal The 5v regulator on the board I bought works nicely though as it is currently holding the PDA's DTR line high ( a requirement ) However, it still begs the questions:- 1. why didn't it work? 2. can those data transformations really be just a coincidence? 3. do I need to get out a lot more? 4. would I look good with a monocle? Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 Hi Steve Did you get the mail re setting parity and stop bits etc If information is getting through - which from reading the thread it appears to be, then I would suggest that it points to a protocol setting not a physical electrical problem Melf (not melt - is it sad that we both have views on this ) Hi Mel, You have pm Quote
melt Posted August 16, 2005 Posted August 16, 2005 Hi Steve Did you get the mail re setting parity and stop bits etc If information is getting through - which from reading the thread it appears to be, then I would suggest that it points to a protocol setting not a physical electrical problem Melf (not melt - is it sad that we both have views on this ) Hi Mel, You have pm melf or melt, Mel, you have PM, this is all getting confusing, think I need to go and lie down mel That's melt not melf, I think! Quote
scott beeland Posted August 16, 2005 Posted August 16, 2005 However, it still begs the questions:- 1. why didn't it work? 3. do I need to get out a lot more? 4. would I look good with a monocle? Answered your own questions there I think fella 1) Does it matter? 2) YES 3) Probably not Quote
Martin Keene Posted August 16, 2005 Posted August 16, 2005 He lost me after here... Hi folks, I wonder if you can help with an RS232 problem? I want to drive my telescope from my Sony Clie PDA Quote
Blatman Posted August 16, 2005 Posted August 16, 2005 I think i'll be looking at my Dad's telescope in a different light from now onwards You're supposed to look *through* them, not at them, and generally in the dark... You know what, I should be looking through mine and not fart a**ing around with the electronics - it was a clear sky last night and I was soldering not viewing Which reminds me... I bought Blatgirl a star a while back (yeah, I know...). Got a nice star chart with co-ordinates and it's "proper" nomenclature. Trouble is, I can't read star charts... At some point in the future, could I invite Blatgirl and myself round to Chez Wolf and trouble you for some star location services? It would be nice to show her what I bought her. I just hope the natives are friendly over in the Gamma Quadrant... Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 At some point in the future, could I invite Blatgirl and myself round to Chez Wolf and trouble you for some star location services? It would be nice to show her what I bought her. I just hope the natives are friendly over in the Gamma Quadrant... How sweeeeet .... No problem, now that I can drive my telescope from either my PDA or my laptop, I can swing round onto any object whose RA and DEC are recorded - alternatively, the star in question may have an NGC number or something equivalent that I can also locate on. If it is actually visible from my humble observatory, I can take a photograph of it for you if you like! Quote
steppenwolf Posted August 16, 2005 Author Posted August 16, 2005 Answered your own questions there I think fella 1) Does it matter? You see, this is the sad thing - it DOES matter! I just know that even though I have got the end result I wanted without the component I bought, the 'scientist' ( aka anorak ) in me just has to know what went wrong. Its what keeps me so young looking ... Quote
Blatman Posted August 16, 2005 Posted August 16, 2005 At some point in the future, could I invite Blatgirl and myself round to Chez Wolf and trouble you for some star location services? It would be nice to show her what I bought her. I just hope the natives are friendly over in the Gamma Quadrant... How sweeeeet .... No problem, now that I can drive my telescope from either my PDA or my laptop, I can swing round onto any object whose RA and DEC are recorded - alternatively, the star in question may have an NGC number or something equivalent that I can also locate on. If it is actually visible from my humble observatory, I can take a photograph of it for you if you like! A photo would be extremely cool. I'll get back to you with co-ordinates and an estimate of how long it takes to get there at warp 5. Phasers on stunned... Quote
corsechris Posted August 16, 2005 Posted August 16, 2005 Steve, Result. I'm no fan of these half-arsed pseudo 232 drivers so commonly used. What good is a standard if some penny-pinching bean counter decides that to save 3p they'll do without a proper set of voltage rails. Pah. I love serial comms. 3 wires and days of trauma!! And to all those nay-sayers out there...without this sort of thing, you'd all still be driving cars with clockwork ignition and carburettors. Oh, you are..... I'll get me coat....... Quote
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