Date:         Sun, 27 Dec 1998 00:52:08 -0600   From:         "Chuck Shaw" <cshaw@ghg.net>     To:         <Spsweene@aol.com>>****************>   The only change I think is necessary is putting the diode D1 in theother direction.>***************> So, can you do me a favor?   Please send how you wired things up to that> bipolar motor for me> **********>Hook up one winding to pins 6 & 7 and the other winding up to pins 8 & 9.>The remander of the pins are un used for bipolar motors.>************I understand.  Thats what I had decided would work too.  Thanks for theconfirmation.  I do not use Bi-polars and do not know too many folks thatdo, but will be able to use the circuit for them.>******>I haven't had the chance to test it but using a 1K  resistor in series with>the base of a TIP120 for each of the pins 6,7,8, 9  the Emitters connectedto>ground and the collectors connected to the windings with the center taps>connected to V + should work.I know this configuration works (I have used it for over 2 years on mycurrent scope).  Actually I run the 12v into the collectors and then theoutputs of the emitters go to each of the windings, with the center taps alltied together and returning to pins 1-5 on the DB9.  I cut the traces infront of and behind 1-5 to allow the return path from the motor to use theDB9 connector. (I had to jumper around the cut out portion of the trace tocontinue the power distribution on the PCB that went through pins 1-5).Hooking up the power to the center taps means voltage is present all thetime in the line going to the motor instead of only when a winding is beingpulsed.  Good engineering practice has trained me to NOT have live wireswhen I can avoid it <G> to reduce the risk of shorts... (small risk on thisI know, but habits are habits!!!  Your way will work fine)Look at the other mods I was suggesting also when you get the chance.  UsingVcc vs Motor power for the chip is one mod, the other is the choice ofseries resistors.  If you have a motor running on this circuit I guess theresistor sizes are OK!!! <g>See ya,ChuckDate: Fri, 4 Dec 1998 23:55:13 -0600From: "Chuck Shaw" <cshaw@ghg.net>To: <mbartels@bbastrodesigns.com>, <spsweene@aol.com>CC: <iss@pvtnetworks.net>Mel, Pat (and FYI Andy),I scanned the PCB and drew in the places that I think need to be modifiedper the suggested schematic changes in my previous note (see below).  Thefiles are not saved at the highest quality settings for .jpg's to keep thefiles small. Let me know if they view OK....  I can send the slightly betterquality (albeit about 2x as large) files if you want them.PCB1b.jpg is the top of the PCB, and shows change #3 (the change in polarityof D1)PCB2b.jpg shows the bottom of the PCB and shows changes 1, 2A, and 2B.Change 1 is actually in 4 parts:Part 1-1 cuts the trace from the Optoislator pin 4 to groundPart 1-2 cuts the trace from SAA1042 pin 7 to Optoisolator pin 5Part 1-3 installs a jumper from SAA1042 Pin 7 to Optoislator pin 4Part 1-4 installs a jumper and 1 Meg resistor from SAA1042 pin 7 to groundChange 2A is actually in 3 parts:Part 2A-1 cuts the trace coming from the motor power to the FR DB 9connectorPart 2A-2 cuts the Motor Power trace leaving the FR DB9 connector the goesto the other connectorsPart 2A-3 jumpers the Motor Power trace around the cut out section passingthrough the FR DB9 connectorChange 2B is a jumper to connect the return path ground pins for the FR DB-9connector to ground.Lemme know if any of you see something I did wrong in these suggestedchanges.....See ya,Chuck-----Original Message-----From: Chuck Shaw <cshaw@ghg.net>To: mbartels@bbastrodesigns.com <mbartels@bbastrodesigns.com>; spsweene@aol.com <spsweene@aol.com>Cc: iss@pvtnetworks.net <iss@pvtnetworks.net>Date: Thursday, December 03, 1998 4:56 PMSubject: PCB Update>Pat and Mel (and FYI for Andy),>>I have been looking at the FR portion of the circuit board and I think I>have found 3 things that need to be changed to make the FR portion of the>circuit work "correctly".>>I enlarged a portion of the circuit schematic and drew in the updates.>There are 4 places that need to be looked at....  1, 2A, 2B, and 3.  Eachis>circled and numbered.  Look at the attached file (fr-pcb2.gif) and refer to>the comments below....>>1.  The "clock" for the SAA1042 is active on the positive edge of the clock>pulse.  The circuit, as drawn seems to take the "high" pulse from Pin 1 of>the Parallel port, and cause the 2N222 to conduct, which allows the>optoisolator to then  conduct, which shorts the VCC voltage and changes the>pin 7 input from normally high (thru the 4.7k resistor) to low.    This>makes the "leading edge" coming from the PC's pin 1 into a trailing>edge..... I am not sure what effect that really has, but I thought I might>as well drive the chip the way it expects to be driven.     I removed the>ground on the optoisolator and instead directed the emitter to pin 7, and>cut the line from the input of the optoisolator to pin 7.  I also added a 1>megohm resistor to make very sure the clock signal went to zero when the>opto isolator stopped conducting, yet would not draw down the voltage too>much when it WAS conducting....     Not sure if 1 MEG is the right value,or>even if it is needed (I do not have that resistor in my current circuit Iam>using, but, what the heck.....)>>2.  This is actually two parts:  The problem is the FR motor has no return>path.....  DB9 Pins 6, 7, 8,& 9 get set high from the SAA1042's pins 14,16,>1, & 2 (motor power enters the SAA1042 via pin 15, and exits via the 4 pins>mentioned).  The return path should be via pins 1, 2, 3, 4, & 5,  but those>pins are high too (from motor power)????  The fix is two changes:>>2A.  Cut the line from the motor power source to pins 1, 2, 3, 4, & 5>>2B.  Ground (to the motor power ground) pins 1, 2, 3, 4, & 5>>>The SAA1042 will then provide motor power thru the chip itself to the FR>motor.   Problem is, the chip is only rated at 500ma (with a heat sink>attached to pins 4/5/12/13).   Most FR steppers will draw more than that as>they sit for relatively long periods of time on single and double windings>energized.  So, I recommend taking the outputs from pins 6, 7, 8, and 9 and>sending them, thru an appropriate dropping resistor (remmber the input>voltage is the 12-24v motor power, not 5v VCC), to the bases of TIP 120's.>The TIP 120's would then have each of their collectors tied to the motor>power source.  The emitters of each of the TIP 120's would be tied back to>the appropriate motor windings, and then the motor windings get attached to>pins 1, 2, 3, 4, (and 5) which provides the return path.   The TIP 120's>should probably be heat sinked also...... The FR motor does not have the>current limiting benefits of Mel's software....>>3.  The Small Zener Diode between pins 2 and 15 seems to be drawn in with>its polarity backwards according to the Motorola data sheet on the>SAA1042.....  While the Zener is not strictly required for the system to>work properly (it is there to protect against large spikes generated from>the motor coils), it should be installed correctly if used....  If notused,>then pins 2 and 15 need to be tied directly together.>>>I have not looked at the PCB itself to see which traces need to be broken>and where, and where the best places to add jumpers are, but I will do so>and send that along (I scanned the PCB so I can provide a drawing update).>I think the changes are pretty easy though.....>>Lemme know if you guys think I am screwed up on these changes, but I"think">I have it right... <G>>>See ya,>>Chuck>>p.s.  Mel, I have the gear train re-installed on my scope, and we should>have some clear enough wx coming in the next couple of days to test drive>the "PEC on the FLY" update.....  I can't wait!!!  That would be a MAJOR>capability!!!  Gotta see about STS-88 getting lauched first though......>switch problems are a bitch, whether on a scope or a Shuttle!!!!>