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Arduino SCSI device - Work in Progress


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On 10/28/2020 at 7:53 AM, Chopsticks said:

also might be a handy idea to add a standard HDD power connector to your pcb

 

On 10/28/2020 at 2:03 PM, erichelgeson said:

There is no need, it is powered by the SCSI bus.

 

I have had issues with some of "the competition" (as it were) on some machines where the SCSI bus doesn't seem to provide quite enough juice, even though it ought; there are a couple of models that seem particularly prone to this.  So it may be worth putting one on if room can be found, perhaps even a small floppy-style one.

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5 minutes ago, cheesestraws said:

 

 

I have had issues with some of "the competition" (as it were) on some machines where the SCSI bus doesn't seem to provide quite enough juice, even though it ought; there are a couple of models that seem particularly prone to this.  So it may be worth putting one on if room can be found, perhaps even a small floppy-style one.

interesting, i should probably, check how much current the se/30 can provided on the scsi 5v termination line compared to the current draw of this hdd emulator, as well as the current draw of the microsdcard i was using.

perhaps its not a problem on more 'modern' vintage macs?

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Just now, Chopsticks said:

perhaps its not a problem on more 'modern' vintage macs?

 

I don't think it's even that; my suspicion is that it's just slightly borderline design on a couple of models.  Earlier ones and later ones both seem to work.  Though I haven't looked into this scientifically other than sighing and finding workarounds :-), so take this with a pinch of salt.

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2 minutes ago, cheesestraws said:

 

I don't think it's even that; my suspicion is that it's just slightly borderline design on a couple of models.  Earlier ones and later ones both seem to work.  Though I haven't looked into this scientifically other than sighing and finding workarounds :-), so take this with a pinch of salt.

thats interesting to know, i guess maybe the se/30 is one of those borderline designs?
 

i gave up on this device awhile ago anyways, it was to slow compared to the hdd i have in my mac currently, still considering how cheap it is to buy the micro and the pcb im sure this is a great option for many people

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3 hours ago, cheesestraws said:

 

I don't think it's even that; my suspicion is that it's just slightly borderline design on a couple of models.  Earlier ones and later ones both seem to work.  Though I haven't looked into this scientifically other than sighing and finding workarounds :-), so take this with a pinch of salt.

It may not even be a matter of current. I noticed while poking around with my SE/30 that there appears to be a Schottky diode drop on the SCSI termination power rail, resulting in a voltage of about 4.6V iirc. This makes sense, as you don't want another device on the SCSI chain also providing term power (like my CD-ROM does) "fighting" with the power supply. This might just be marginal enough even with the low dropout of the regulator on the Blue Pill that the processor isn't getting enough voltage. And I imagine some Blue Pills have better LDOs than others, considering everybody makes them.

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On 10/26/2020 at 10:16 PM, erichelgeson said:

Got the mouser order tonight - BlueSCSI 1.0-a fully assembled - tested termination - works!

Sweet! Is this considered "ready to go" and should I order some boards from your plans or are you going to do another rev or two before you call it finished?

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2 hours ago, nyankat said:

It may not even be a matter of current. I noticed while poking around with my SE/30 that there appears to be a Schottky diode drop on the SCSI termination power rail, resulting in a voltage of about 4.6V iirc. This makes sense, as you don't want another device on the SCSI chain also providing term power (like my CD-ROM does) "fighting" with the power supply. This might just be marginal enough even with the low dropout of the regulator on the Blue Pill that the processor isn't getting enough voltage. And I imagine some Blue Pills have better LDOs than others, considering everybody makes them.

hmm that's likely it then, as 4.6v is on quite the low end of the scale and it probably means that even if the stm chip turns on it would be triggering brown out detection and constantly reseting itself

 

does anyone know just how many Macs are effected by this? as if its only a few models it probably doesn't matter but if it is common to many models it would probably be a good idea to add a power connected to the board with a. 3 pin header to allow people to select either termination power or power from an external source through the power connector (hope that makes sense), the small increase if PCB footprint size would barely have any effect on the overall cost of getting boards manufactured so its probably something worth exploring?

also these bluepill boards can be overclocked a bit and I wonder if that would improve the overall speed of scsi transfers?

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16 hours ago, Chopsticks said:

check how much current the se/30 can provided on the scsi 5v termination line

Please do and let me know - I guess all of my machines provide a good 5v - but if that's not common (and probably with 30 year old machines it varies) it would be a good idea to have a 5v line. An option is they do make molex to usb to provide 5v, but they're a bit hard to source. I'll look at the cost and layout.

 

10 hours ago, Chopsticks said:

also these bluepill boards can be overclocked a bit and I wonder if that would improve the overall speed of scsi transfers?

This is something I'll try this weekend, I've noticed the option, just never selected it.

 

12 hours ago, nyankat said:

Is this considered "ready to go"

The scsi termination works well. Would just adding niceties to it now - eg: 5v Power, activity LED pin out, fix placement of debug pins (not enough room), likely remove fuse, remove 2nd hole as there is not enough room to use it, 3d print a bracket. But all that said it works well and I'm testing/using this rev (and ztto's rev) daily. If you're comfortable figuring out any issues you run into yourself 1.0-a is ok for you. If you want a set it and forget it - let me think on a few of these items - likely a 1.0-b will be happening soon.

 

Since there is quite a bit of demand I'm considering doing an order of 100 (shipping really kills the deal for small batches) I do have 2 1.0-a's and 3 ztto v2's if anyone wants a blank now - with the expectation of feedback.

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12 minutes ago, erichelgeson said:

Please do and let me know - I guess all of my machines provide a good 5v - but if that's not common (and probably with 30 year old machines it varies) it would be a good idea to have a 5v line

 

FWIW, on a couple of IIsi boards I have here, putting any actual load on the power seems to drop the voltage to about 2.5v.  I really think a 5v in is a good idea if there's room for it.

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Re power, might it be best to add a floppy power connector to the PCB design, but leave it unpopulated? That would take little space on the board and wouldn’t change the BOM, but if anyone had issues using term power it would be trivial to solder in the connector.

 

also, I’m definitely in for a few PCBs.

Edited by Michael_b
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