Thread
Terminating cheapo SCA -> 50Pin SCSI adapters
As requested I took some pictures building the Mark 2 of these adapters so anyone interested could put them together
Parts:
Chepo 80Pin SCA to 50 Pin adapter (http://www.ebay.co.uk/itm/130772715339)
18x 110ohm resistors, i suggest you use 1/8 watt or you will be pushed for space (1/4 should just about be ok) (http://cpc.farnell.com/_/mf25-110r/resistor-0-25w-1-110r/dp/RE03728)
OR 110 Ohm resistor packs pulled from dead drives
1x 1N4001 diode (or anything similar) if your adapter doesn't have a diode on it already you will need 2 (though i haven't seen any without it)
1x Small electrolytic cap (I used a 10uF non polarized one, any small value should work, and it dosen't need to be NP, just the ones i have are)
Total cost of the parts should be under £2
This adapter just terminates the lines on the 50 pin connector, it will not help with any fussy SCA drives that want their extra data lines terminated.
First thing is to solder the 110 ohm resistors, Connect all the tops of them together:
Then the cap, which goes between the the common contact of the resistors and ground, i find the best thing is to fold the legs other tho the other side of the board:
And finally, solder the diode between the side of the term power jumper closest to the edge of the board and the common contact of the resistors. Cathode towards the resistors.
Also I recommend you cut the trace going from the term power to the 50 pin connector, otherwise you may find in some macs you cannot switch off termination.
Installed and it works
Parts:
Chepo 80Pin SCA to 50 Pin adapter (http://www.ebay.co.uk/itm/130772715339)
18x 110ohm resistors, i suggest you use 1/8 watt or you will be pushed for space (1/4 should just about be ok) (http://cpc.farnell.com/_/mf25-110r/resistor-0-25w-1-110r/dp/RE03728)
OR 110 Ohm resistor packs pulled from dead drives
1x 1N4001 diode (or anything similar) if your adapter doesn't have a diode on it already you will need 2 (though i haven't seen any without it)
1x Small electrolytic cap (I used a 10uF non polarized one, any small value should work, and it dosen't need to be NP, just the ones i have are)
Total cost of the parts should be under £2
This adapter just terminates the lines on the 50 pin connector, it will not help with any fussy SCA drives that want their extra data lines terminated.
First thing is to solder the 110 ohm resistors, Connect all the tops of them together:
Then the cap, which goes between the the common contact of the resistors and ground, i find the best thing is to fold the legs other tho the other side of the board:
And finally, solder the diode between the side of the term power jumper closest to the edge of the board and the common contact of the resistors. Cathode towards the resistors.
Also I recommend you cut the trace going from the term power to the 50 pin connector, otherwise you may find in some macs you cannot switch off termination.
Installed and it works
Thanks glad i could contribute something usefull 
and i should have probably noted, the contacts you solder the resistors to are:
r r r r r r r r o r o o o o o o r r r r r r r r r
o o o o o o o o o o o o o o o o o o o o o o o o o
(that is with the 50 pin connector towards you) r = resistior o = no resistior
glad i could contribute something usefull and i should have probably noted, the contacts you solder the resistors to are:
r r r r r r r r o r o o o o o o r r r r r r r r r
o o o o o o o o o o o o o o o o o o o o o o o o o
(that is with the 50 pin connector towards you) r = resistior o = no resistior
yes, let me take pics of my one using resistor packs from a dead 120mb quantum pro drive ELS it is much much neater
I did consider using SMT parts, however i find they are very fiddly in situations like this, However an interesting idea would be to produce a small cuircuit board using smt parts, with pads right at the edge of the board. Then you could just stick the board down and solder it right to the pins, easy and neat (like the QSB's used in the xbox modding community)
EDIT: Here is mk1, using the res packs, however it is permanently terminated
I did consider using SMT parts, however i find they are very fiddly in situations like this, However an interesting idea would be to produce a small cuircuit board using smt parts, with pads right at the edge of the board. Then you could just stick the board down and solder it right to the pins, easy and neat
(like the QSB's used in the xbox modding community)EDIT: Here is mk1, using the res packs, however it is permanently terminated
I thought for some more modern drives you needed to terminate some pins of the 80pin connector, so the drive would know that it is being used with ancient things?
That or use a 68pin cable with it's own terminator on the end and hook that to the motherboard and drives with adapters.
That is what I remember hearing anyway.
That or use a 68pin cable with it's own terminator on the end and hook that to the motherboard and drives with adapters.
That is what I remember hearing anyway.
Yes that is correct, some 80pin drives need the extra lines terminated, whereas others don't, so this will only work for ones which don't need them terminated
I do plan to make one that terminates the extra lines on the 80 pin connector, but first i need to find a drive that doesn't work without doing that
I do plan to make one that terminates the extra lines on the 80 pin connector, but first i need to find a drive that doesn't work without doing that
I have a Compaq BD0366459B (36GB 10k RPM) that appears to need termination on the 80pin, or use a 68pin cable.
I can just use it with a 68pin cable but in a cramped space that might not be as nice unless I also used a flexible extension on the mobo side of the the 68 to 50 pin adapter.
*shrug*
I can just use it with a 68pin cable but in a cramped space that might not be as nice unless I also used a flexible extension on the mobo side of the the 68 to 50 pin adapter.
*shrug*
initial tests with the BD0366459B seem sucessfull, it is recognized and is currently being formatted.
Once it is formatted I will test it on the adapter without the extra lines terminated and see if it still works
Edit, well, it seems that it gets it recognised where it otherwise wouldn't. However it failed in formatting and is now saying it can't get the required data from the disk...
Once it is formatted I will test it on the adapter without the extra lines terminated and see if it still works
Edit, well, it seems that it gets it recognised where it otherwise wouldn't. However it failed in formatting and is now saying it can't get the required data from the disk...
Wow, a new record! the drive failed after being powered up for 10 min... so much for fully tested.
oh well, hoefully the seller will agree to just send me annother.
However, the test was successfull, the drive was recognized using mk3 of the adapter, where it wasn't with mk2
oh well, hoefully the seller will agree to just send me annother.
However, the test was successfull, the drive was recognized using mk3 of the adapter, where it wasn't with mk2
I like that idea, I've been using cable-end terminators for drives that need them but this is a tidy approach for space-cramped compact and pizzabox machines.
YMMV but I've found that the Savvio drives seem to work fine without any additional termination. I assumed the drives have onboard termination but I could simply be lucky.
YMMV but I've found that the Savvio drives seem to work fine without any additional termination. I assumed the drives have onboard termination but I could simply be lucky.
Yeah, it is really just the luck of the draw weather a drive requires extra termination. For ones that don't there is no need to add the extra 8 resistors.
Using inline terminators was what i originally intended to to, however i decided just to see if i could just add the termination to the board.
However i guess the real use of these is not so much for the termination, but to allow some more picky drives to be used
Using inline terminators was what i originally intended to to, however i decided just to see if i could just add the termination to the board.
However i guess the real use of these is not so much for the termination, but to allow some more picky drives to be used
thanks
Tbh it was less of research and more of just probing a dead hdd to find out how it was terminated, and then a little guesswork
Hopefully this will allow a much wider range of drives to be used in these old macs, i'm planning to buy a random sample of whats on ebay and see which work
Tbh it was less of research and more of just probing a dead hdd to find out how it was terminated, and then a little guesswork
Hopefully this will allow a much wider range of drives to be used in these old macs, i'm planning to buy a random sample of whats on ebay and see which work
Your right there actually, I guess I can call it R&D then
Also, anyone else have a recommendation of a picky drive I should try next? If not I'll just grab the first sub £10 sca drive my next eBay search brings up (actually I did find a lot of 5 36gb sca's for a little over £20, very tempting...)
Also, anyone else have a recommendation of a picky drive I should try next? If not I'll just grab the first sub £10 sca drive my next eBay search brings up (actually I did find a lot of 5 36gb sca's for a little over £20, very tempting...)
Got a new drive today, and it has a interesting feature, it can be set to narrow or wide mode...
in wide mode it needs the extra lines terminated, but in narrow mode it dosen't
the drive is a 9.1gb 7k2 rpm compaq bb009135b4 (or a fujitsu mah3091mc - it is the same drive) i wonder if this is common on ultra 2 drives?
(i must add i haven't tried it on a 68k yet, just on the g4 qs, but i don't see why it wouldn't work)
in wide mode it needs the extra lines terminated, but in narrow mode it dosen't
the drive is a 9.1gb 7k2 rpm compaq bb009135b4 (or a fujitsu mah3091mc - it is the same drive) i wonder if this is common on ultra 2 drives?
(i must add i haven't tried it on a 68k yet, just on the g4 qs, but i don't see why it wouldn't work)
I have to disagree with you, Uni. There's no problem with forming a theory and sharing it. It's not as though he said it worked when he hadn't tested it. Hopefully he will test it and share the results.
We're all here to learn, as well as help, one another; share knowledge, experience, and theory, no?
We're all here to learn, as well as help, one another; share knowledge, experience, and theory, no?
yeah it works
I do understand what uniserver said - these macs can be picky
my assumption was because this drive had a setting to set weather the drive was on a narrow or wide bus
they do seem to be much less picky with all the lines terminated though, i plan to continue testing random drives like this
I do understand what uniserver said - these macs can be picky
my assumption was because this drive had a setting to set weather the drive was on a narrow or wide bus
they do seem to be much less picky with all the lines terminated though, i plan to continue testing random drives like this
Not trying to poke at anyone, Its just, this is not in the lounge, and wouldn't want a ton of people to flock to ebay and buy up hd's only for them to not work.
thats all.
For sure these terminating adaptors he is making are very awesome! They will save people time and money.
and not to mention his solution is more compact/integrated then any other solution out there.
There was a nice solution OWC was selling, but not any more. This solution is next best inline!
So to conclude, For people that might come across this,
There are some SCSI hard drives out there that will work good in Vintage Macs, (with this adaptor he is selling)
We need to make a thread that has a standard format, with a photo of the Hard drive that works, then specifications of it. Maybe with current price per.
Obviously cheaper is better Great Availability is also pretty nice too
Also when in doubt, one could purchase a working scsi hd from me for $20 ea (ready-to-use)(will ship international) To be used with one of these fine
#Terminated SCA adaptors#.
thats all.
For sure these terminating adaptors he is making are very awesome! They will save people time and money.
and not to mention his solution is more compact/integrated then any other solution out there.
There was a nice solution OWC was selling, but not any more. This solution is next best inline!
So to conclude, For people that might come across this,
There are some SCSI hard drives out there that will work good in Vintage Macs, (with this adaptor he is selling)
We need to make a thread that has a standard format, with a photo of the Hard drive that works, then specifications of it. Maybe with current price per.
Obviously cheaper is better
Great Availability is also pretty nice too Also when in doubt, one could purchase a working scsi hd from me for $20 ea (ready-to-use)(will ship international) To be used with one of these fine
#Terminated SCA adaptors#.
I do agree with uni, that is why i did add that note, the only reason i didn't test it on a 68k first is because i had just got in from collage and didn't fancy waiting the half hour it can take my 450 to format a large hdd
A list is a good idea, i would add that it might be a good idea to add weather a drive needs the extra lines terminated or not
A list is a good idea, i would add that it might be a good idea to add weather a drive needs the extra lines terminated or not
Got my latest drive, a 18.4GB compaq
And it is not compatible, although it works in my G4 QS with a scsi 1 card it dose not work in 68k's
Drive model number is:BD01864552
So there's one to avoid.
will see if it works on the 8600's fast scsi bus.
Also got my order of SCSI -> 50 pin adapters, just hopeing my reel of 0805 110R smd's is going to turn up in the next few days so i can get to work on these adapters...
And it is not compatible, although it works in my G4 QS with a scsi 1 card it dose not work in 68k's
Drive model number is:BD01864552
So there's one to avoid.
will see if it works on the 8600's fast scsi bus.
Also got my order of SCSI -> 50 pin adapters, just hopeing my reel of 0805 110R smd's is going to turn up in the next few days so i can get to work on these adapters...
Thanks Just glad people find them usefull
uni, yeah, just updated it with more accurate postage prices
And i have a question, how critical is the value of the termination resistiors? i would like to use resistior packs but 110ohm ones are dam near impossible to find.
I have a laptop -> desktop scsi adapter here that uses 150 ohm resistiors that seems to work fine, however 9 element 150ohm packs are just as hard to find
Just glad people find them usefulluni, yeah, just updated it with more accurate postage prices
And i have a question, how critical is the value of the termination resistiors? i would like to use resistior packs but 110ohm ones are dam near impossible to find.
I have a laptop -> desktop scsi adapter here that uses 150 ohm resistiors that seems to work fine, however 9 element 150ohm packs are just as hard to find
So, since my last post uniserver brought my attention to the fact the price of these adapters have skyrocketed (hopefully this will only be a temporary thing), and as i only have 3 left i decided to look into the viability of producing a proper PCB for these
After a bit of fiddling in EAGLE (and a lot of swearing at it keeping joining electrical connections for no good reason) i ended up with this:
[attachment=0]Screen Shot 2014-01-26 at 16.13.18.png[/attachment]
It needs a bit of neatening up and having the silkscreen added, but it all fits (just about) (btw, a few of the scsi data traces look shorted in that, they aren't it's just how it looks in that pic)
Weather or not this will turn out to be viable is still to bee seen, PCB production prices are so high in the UK if i had them made here it would push the price to something like £20 each. So i guess i will look at pcb fabrication services in the US to see if i can get a better price
After a bit of fiddling in EAGLE (and a lot of swearing at it keeping joining electrical connections for no good reason) i ended up with this:
[attachment=0]Screen Shot 2014-01-26 at 16.13.18.png[/attachment]
It needs a bit of neatening up and having the silkscreen added, but it all fits (just about) (btw, a few of the scsi data traces look shorted in that, they aren't it's just how it looks in that pic)
Weather or not this will turn out to be viable is still to bee seen, PCB production prices are so high in the UK if i had them made here it would push the price to something like £20 each. So i guess i will look at pcb fabrication services in the US to see if i can get a better price
Don't suppose anyone here knows where i could get hold of some of the sca connectors? digikey has them, but at ~£7.50 each + £12 shipping to the uk it's a bit steep
Looks like pcb manufacture isn't going to be too bad, so i'm gonna refine the board a bit more and put in a order later this week
just finding those dam SCA connectors....
Looks like pcb manufacture isn't going to be too bad, so i'm gonna refine the board a bit more and put in a order later this week
just finding those dam SCA connectors....
you will have to get your SCA connectors direct from china…you might have to buy them 1000 or 2000 at a time…
but for pennies each..
i am one step away from buying my caps direct from china… and bypassing mouser all together.
the savings is mind boggleing. like some caps are .0003 ea LOL!
but for pennies each..
i am one step away from buying my caps direct from china… and bypassing mouser all together.
the savings is mind boggleing. like some caps are .0003 ea LOL!
Yeah i was thinking of that, where would the best place be to get them for china? normally i order my Chinese parts off ebay but there's none on there
either that or i'll buy a bunch or the cheap 68 - 80 pin adapters and use hot air to sweat the connectors off, i don't want to do that but it should be possible
either that or i'll buy a bunch or the cheap 68 - 80 pin adapters and use hot air to sweat the connectors off, i don't want to do that but it should be possible
ok here is the guy that i was buying my SCA to 50 pin adaptors from…
http://www.ebay.com/itm/SCA-80-ADAPTER-TO-68-PIN-ULTRA-SCSI-II-III-LVD-SE-C-/280498842646?pt=US_Drive_Cables_dapters&hash=item414f08ac16
i see he is selling a SCA adaptor for the same price… 1.61 but…. its SCA, but not to 50 pin scsi.
i cannot find SCA connectors for sale anywhere on the net.
maybe you will have to break down and make some calls to some factories in china….
http://www.ebay.com/itm/SCA-80-ADAPTER-TO-68-PIN-ULTRA-SCSI-II-III-LVD-SE-C-/280498842646?pt=US_Drive_Cables_dapters&hash=item414f08ac16
i see he is selling a SCA adaptor for the same price… 1.61 but…. its SCA, but not to 50 pin scsi.
i cannot find SCA connectors for sale anywhere on the net.
maybe you will have to break down and make some calls to some factories in china….
Aha! found a uk supplier with the SCA connector -> http://uk.rs-online.com/web/p/pcb-sockets/7293842/
Not exactly cheap at £3.56 a piece, not listed as a SCA connector but my measurements make it the same
They will do for initial testing, once it comes to actually producing any for sale i'll harvest them from the Chinese boards
-> http://uk.rs-online.com/web/p/pcb-sockets/7293842/Not exactly cheap at £3.56 a piece, not listed as a SCA connector but my measurements make it the same
They will do for initial testing, once it comes to actually producing any for sale i'll harvest them from the Chinese boards
Anyone here have experience with making PCB's?
looking to use this service: http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418002.html
got all they way to generating the gerbers (using the file on the download tab on that site)
but i seem to be missing this file: Outline layer: pcbname.GKO
anyone know how i generate it?
looking to use this service: http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418002.html
got all they way to generating the gerbers (using the file on the download tab on that site)
but i seem to be missing this file: Outline layer: pcbname.GKO
anyone know how i generate it?
Dear dreammacys,
hey i see you are selling these 68 to LVD…
i need SCA 68pin to SCSI 50pin…
you used to sell them just a few months ago…
what happened? i need like 50!!!
please let me know!
- morestuffuniwho
yeah man get those in… thanks… you were my guy… the only guy on the planet selling these for a reasonable price.
not only me but i know of a guy in the UK that buys these from you and ADDS termination with some caps and resistors
because they do not naturally come with termination. i don't thin 9 cents is going to effect peoples buying habits of them.
ThankYou!
- morestuffuniwho
hey i see you are selling these 68 to LVD…
i need SCA 68pin to SCSI 50pin…
you used to sell them just a few months ago…
what happened? i need like 50!!!
please let me know!
- morestuffuniwho
Dear dreammacys,
yeah man get those in… thanks… you were my guy… the only guy on the planet selling these for a reasonable price.
not only me but i know of a guy in the UK that buys these from you and ADDS termination with some caps and resistors
because they do not naturally come with termination. i don't thin 9 cents is going to effect peoples buying habits of them.
ThankYou!
- morestuffuniwho
I've not used itead, but I've used Seeed and Smart Prototyping to make PCBs, and been mostly happy with both.
GKO is apparently the keep-out area, though I don't remember seeing it generated when I make a board with Eagle. See http://www.4pcb.com/pcb-file-submissions.html
Yeah seems the .GKO is supposed to have the keep out layer in it
However this http://digital-diy.com/forum/eagle/gerber-board-outline-layer-t2158.html says that what ITEAD actually want in the file is the dimensions layer
It seems it may not be needed, but i'll include it anyway
Also seems i need to move the outline of the board to the dimensions layer.
However this http://digital-diy.com/forum/eagle/gerber-board-outline-layer-t2158.html says that what ITEAD actually want in the file is the dimensions layer
It seems it may not be needed, but i'll include it anyway
Also seems i need to move the outline of the board to the dimensions layer.
Placed the order, so i guess i'll be seeing if the gerbers are formatted right soon (i can't think why there would be any problem with them)
Now... back to seeing if i can find cheap SCA connectors, don't really want to harvest them from chineese boards of i can avoid it
Now... back to seeing if i can find cheap SCA connectors, don't really want to harvest them from chineese boards of i can avoid it
yeah i dont blame you…
i am sure they get them from a distributor over there.
there is a phone number on this SCA to 50 pin adaptor i have here
tel 13316907839
- maybe you could call them and as to buy just some SCA connectors… if no…. then ask where they get them from.
never hurts to ask.
even jobs said him self said:
i am sure they get them from a distributor over there.
there is a phone number on this SCA to 50 pin adaptor i have here
tel 13316907839
- maybe you could call them and as to buy just some SCA connectors… if no…. then ask where they get them from.
never hurts to ask.
even jobs said him self said:
Two thoughts, and I wish I had seen this before you ordered boards.
First, you might email your supplier of SCA to 50 pin adapters and ask him if he can get the components unassembled. You need everything except the circuit board anyway, and it should save him money with his supplier if they just ship the unassembled components.
I don't know if their flow will allow that to work, but it is another avenue, in case you can't get to a SCA connector manufacturer, or in case they want too much volume.
Second, would you mind explaining your termination scheme? It looks to me like you're tieing Term. Pwr. to the signal lines through 110 ohm resistors with a couple of diodes in the line to step down the voltage. I see what you're trying to do, but it is not going to be reliable. According to the literature, you can't count on Term. Pwr. being a reliable 5V. Plus, your voltage seen at the signal pin isn't constant because it depends on the current that flows through the single resistor -- no connection to ground, and that will change as the signal switches between 0 and 1. I'm willing to believe that I've overlooked some trick of electronics that makes this a reliable termination method, but it looks like a contraption for wildly varying termination current/impedance to me.
If one is going to tie the signal pins to Term. Pwr through 110 ohms of resistance, then the Term. Pwr. needs to be a voltage regulated source of 2.85V. This is active termination and it requires an actual voltage regulator in the circuit, such as an LT1086CT.
If you're not going to use a voltage regulator, then the old method of passive termination is to tie the signal pins to ground through 330 ohms and to Term. Pwr. through 220 ohms. This still has the problem that Term. Pwr. may not actually be 5V, but it has the virtue that the voltage at the signal pin is constant because of the voltage divider created between Term. Pwr and ground.
First, you might email your supplier of SCA to 50 pin adapters and ask him if he can get the components unassembled. You need everything except the circuit board anyway, and it should save him money with his supplier if they just ship the unassembled components.
I don't know if their flow will allow that to work, but it is another avenue, in case you can't get to a SCA connector manufacturer, or in case they want too much volume.
Second, would you mind explaining your termination scheme? It looks to me like you're tieing Term. Pwr. to the signal lines through 110 ohm resistors with a couple of diodes in the line to step down the voltage. I see what you're trying to do, but it is not going to be reliable. According to the literature, you can't count on Term. Pwr. being a reliable 5V. Plus, your voltage seen at the signal pin isn't constant because it depends on the current that flows through the single resistor -- no connection to ground, and that will change as the signal switches between 0 and 1. I'm willing to believe that I've overlooked some trick of electronics that makes this a reliable termination method, but it looks like a contraption for wildly varying termination current/impedance to me.
If one is going to tie the signal pins to Term. Pwr through 110 ohms of resistance, then the Term. Pwr. needs to be a voltage regulated source of 2.85V. This is active termination and it requires an actual voltage regulator in the circuit, such as an LT1086CT.
If you're not going to use a voltage regulator, then the old method of passive termination is to tie the signal pins to ground through 330 ohms and to Term. Pwr. through 220 ohms. This still has the problem that Term. Pwr. may not actually be 5V, but it has the virtue that the voltage at the signal pin is constant because of the voltage divider created between Term. Pwr and ground.
Interesting idea on asking for the boards unassembled, since that would give me all the parts. anyway, i'll work more on this once i have the pcb's, the ones i found in the uk are cheap enough for me to do initial testing.
How it is terminated is tieing 5v to the scsi lines through either 110ohm or 150ohm resistors (depending on if i'm using smd's or repacks, so in the case of these it will be 150ohm) plus 2 diodes (i'm using 1n4001's)
I did initially try using a 3.3v voltage regulator but just couldn't ever get it to work
i'll build a quick one using the active termination method at the weekend and see if i can get it working.
How it is terminated is tieing 5v to the scsi lines through either 110ohm or 150ohm resistors (depending on if i'm using smd's or repacks, so in the case of these it will be 150ohm) plus 2 diodes (i'm using 1n4001's)
I did initially try using a 3.3v voltage regulator but just couldn't ever get it to work
i'll build a quick one using the active termination method at the weekend and see if i can get it working.
Everybody keep on the lookout for the dumpster ballast level Sun SPARCstation 5 for some real goodies inside. There's a 2 SCA Drive backplane and cable in there with that's probably one of the very best Active Termination setups ever made! [
] ]'>
After I drill out a bunch of spot welds I'll post a thread about this backplane bonanza. I've (almost literally) been sitting on this Pile-O-SPARCstations I picked up at something like $5 ea. I was filching the purple blank and FDD Bezels out of one of the three 5s in the stack for use in a Sun Tape Drive Case and discovered this gem by accident this morning.
] ]'>After I drill out a bunch of spot welds I'll post a thread about this backplane bonanza. I've (almost literally) been sitting on this Pile-O-SPARCstations I picked up at something like $5 ea. I was filching the purple blank and FDD Bezels out of one of the three 5s in the stack for use in a Sun Tape Drive Case and discovered this gem by accident this morning.
That'd defiantly be interesting to see, do you think it is something that could be replicated in the limited space of the SCA though?
i'll be doing some playing with vreg's after collage tommrow, hopefully i still have some lm317's around, if i can get that working i will switch to using that
i'll be doing some playing with vreg's after collage tommrow, hopefully i still have some lm317's around, if i can get that working i will switch to using that
Ok, i really don't know why i couldn't get this working in the past
Used a bit of a crude setup to do some testing
[attachment=0]photo(20) copy.jpg[/attachment]
I couldn't get exactly 2.85v, but i tried a couple of differen't setups with the lm317, one gave 3.03v and one gave 2.5v. Both worked successfully
Then i tried a 3.3v regulator i had previously tried and that had failed, that also worked
So from now on i will use voltage regulators in all new builds
Used a bit of a crude setup to do some testing
[attachment=0]photo(20) copy.jpg[/attachment]
I couldn't get exactly 2.85v, but i tried a couple of differen't setups with the lm317, one gave 3.03v and one gave 2.5v. Both worked successfully
Then i tried a 3.3v regulator i had previously tried and that had failed, that also worked
So from now on i will use voltage regulators in all new builds
i have been using your adaptors in many different mac's and they have been working out fantastic for me… not one issue.
isn't this what were doing here, passive termination?
http://computer.howstuffworks.com/scsi4.htm
isn't this what were doing here, passive termination?
http://computer.howstuffworks.com/scsi4.htm
i love simplicity. if it works don't fix it…
The big reg is a LM317, just there for testing, will be using LM1117's for the actual adapter
The way they are terminated is actually closer to active termination, as trag mentioned earlier in the thread passive termination entails using two sets of resistors
And there isn't anything wrong with the way i have been doing it, just it relies on the 5v rail being the correct voltage, so if they where used in a computer with a wacked out 5v rail there is a chance you could get some damage (but if you have a wacked out 5v rail your probably gonna damage something anyway)
The regulators don't add any extra cost to the adapter, there a couple of pence each from china, + a tiny square of pcb (which i'll produce myself)
The way they are terminated is actually closer to active termination, as trag mentioned earlier in the thread passive termination entails using two sets of resistors
And there isn't anything wrong with the way i have been doing it, just it relies on the 5v rail being the correct voltage, so if they where used in a computer with a wacked out 5v rail there is a chance you could get some damage (but if you have a wacked out 5v rail your probably gonna damage something anyway)
The regulators don't add any extra cost to the adapter, there a couple of pence each from china, + a tiny square of pcb (which i'll produce myself)
yeah i am pretty sure BMOW has this very same issue with his Floppy Emu, The screen goes weird every time plug it into this 512k i have here, The thing works but might have some dirty power output or something.
maybe i should ask em to put a nice volt meter on the screen of his floppy emu??? that would be useful… pop on and you can see right whats/what. make it more useful and more of a diagnostic tool as well!
maybe just a one liner at the top? +12=XX.XX -12=XX.XX +5=XX.XX
. 5 -12V
. 6 +5V
. 7 +12V
. 8 +12V
or go the extra mile and program in limits… and the floppy emu says… HEY YOUR PSU IS NOT GOOD DOOD! FIX IT! hahah that would be Cool!!
maybe i should ask em to put a nice volt meter on the screen of his floppy emu??? that would be useful… pop on and you can see right whats/what. make it more useful and more of a diagnostic tool as well!
maybe just a one liner at the top? +12=XX.XX -12=XX.XX +5=XX.XX
. 5 -12V
. 6 +5V
. 7 +12V
. 8 +12V
or go the extra mile and program in limits… and the floppy emu says… HEY YOUR PSU IS NOT GOOD DOOD! FIX IT! hahah that would be Cool!!
There's a simple test is you think you have dirty power on the 512k, grab some big caps (1000uf or so) and stick them on the voltage rails on the floppyemu, should give it much cleaner power
Had the same issue with a project i built in my electronics class in school a year or so back, microcontroller went crazy every time i tried to power up the board, after a week of literally checking everything on the board i tried putting a 1000uf cap over the power input, and it worked perfectly from then on. Turns out the power brick i was using wasn't so well regulated
Had the same issue with a project i built in my electronics class in school a year or so back, microcontroller went crazy every time i tried to power up the board, after a week of literally checking everything on the board i tried putting a 1000uf cap over the power input, and it worked perfectly from then on. Turns out the power brick i was using wasn't so well regulated
Actually, I think there was.
With a voltage regulator in there, as you've switched to, when the signal pins are high (2.85 - 5V) there will be some current flow from the signal pin through the 110 ohm resistor to the regulated voltage area, damping ringing on the high end.
Under your previous configuration, when the signal was high, there could be no current flow to damp the ringing because the diodes acting as the voltage regulator would be reverse biased. Using diodes as a voltage regulator only works if the current flow is always in the same direction and if the difference in voltage between the ends is large enough to forward bias the diodes. Neither of these conditions are always met in this application.
I have not given full consideration to how the capacitor may have contributed to the termination, though, hence my earlier request for an explanation of how it was meant to work. It's possible I've overlooked an aspect which would make it work. But based on what I know so far, I really don't think it should work properly -- using a real voltage regulator is a much more robust solution.
Of course, in many instances, even no termination will still allow a SCSI bus to operate, so the fact that some systems with the old style terminators work is not proof that they're doing their job properly.
Anyway, all that said, I think it's great that you're moving to using a real voltage regulator circuit. Nice work.
I do not know enough to answer this question. The specification says to use 2.85V. I imagine that you could get some ringing on the high signals because 3.3V is a little too high and your highs will be a little underdamped, and your lows will be a little overdamped. With slow original SCSI and for these applications, will it ever make a difference, or will it be "good enough"? I just don't know. There was probably a time when I could have calculated/analyzed it, but those days were about a decade ago....
If you can get 2.85V or an adjustable Vreg without blowing the budget, I'd go that route. I think the LM317 is adjustable, but then you need more components. You might hunt around at National Semiconductors, TI, and Linear Tech (I think someone bought NS a year or two ago) in their power and control or voltage regulation sections and identify a few simple chips that can do the job, then hunt them on Ebay to see the pricing. Also, take a look at questcomp.com. Sometimes they have stuff in stock at lower prices than Ebay. The LT1086 is a good choice, if available in a smaller package than I've seen it in, but I don't know about pricing. LT might have something similar with a lower current rating. Oh, it's worth checking Digikey and Mouser as well. Oh, you're in the UK right? So Farnell?
i'll just find some 2.85's then, better to do it correctley now than have to change it again further down the line
This is a good price for them : http://www.aliexpress.com/item/Ams1117-2-85-2-85v-1a-power-supply-voltage-stabilizing/771958640.html
I can't seem to find any uk suppliers that do them for a decent price, so it looks like getting them from china is my only choice
This is a good price for them : http://www.aliexpress.com/item/Ams1117-2-85-2-85v-1a-power-supply-voltage-stabilizing/771958640.html
I can't seem to find any uk suppliers that do them for a decent price, so it looks like getting them from china is my only choice
Yeah that was my worry, However i think i'm going to take the risk. As the cheapest i can find them is from in the uk is from RS, ~30 pence each (+ shipping +a card handling charge as my order would be under £20)
Edit: the best ones from farnell is : http://uk.farnell.com/rohm/bu2jtd3wg-tr/ldo-fixed-2-85v-0-2a-ssop-5/dp/2342945
However the £20 pretax minimum order limit is a real problem for me
Edit: the best ones from farnell is : http://uk.farnell.com/rohm/bu2jtd3wg-tr/ldo-fixed-2-85v-0-2a-ssop-5/dp/2342945
However the £20 pretax minimum order limit is a real problem for me
that website seems fairly massive.
I doubt a vendor would risk getting black listed from such a large sales medium...
but then again ... Ya never know... I would say its worth the 8-10 bucks.
I was going to buy 2000 Murata 16v 47uf ceramic caps from there last fall... for like 206.00 free shipping.
sick deal!
I have not found a deal like that this new year.
mouser also sells that brand.
I doubt a vendor would risk getting black listed from such a large sales medium...
but then again ... Ya never know... I would say its worth the 8-10 bucks.
I was going to buy 2000 Murata 16v 47uf ceramic caps from there last fall... for like 206.00 free shipping.
sick deal!
I have not found a deal like that this new year.
mouser also sells that brand.
I have bought a few items on Alibaba, and always had a good experience, so far. However, they are a marketplace, not a department store, so who knows how well they police their participants.
At the low currents you're dealing with, even if the Vregs are fakes, as long as there is a Vreg in the package and not just empty packages, you're probably okay. They might be rated for a little lower power or have a slower response time, but as long as they hold 2.85V closely, you're probably okay.
At the low currents you're dealing with, even if the Vregs are fakes, as long as there is a Vreg in the package and not just empty packages, you're probably okay. They might be rated for a little lower power or have a slower response time, but as long as they hold 2.85V closely, you're probably okay.
A slightly modified PCB using the proper voltage regulator setup (this was harder that i thought it would be, had to swap a few parts for their SMT equivs)[attachment=0]Screen Shot 2014-02-05 at 22.11.58.png[/attachment]
I'll order these once i have confirmed the boards i have ordered work
I'll order these once i have confirmed the boards i have ordered work