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S-100 backplane project

NobodyIsHere

Veteran Member
Joined
Dec 21, 2006
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Hi All! For some time now I've been working on a side project to make an S-100 backplane. After some feedback, I've got a design for a small 6" x 8" backplane of 6 slots with active termination. I will post an updated ZIP file with the specifics if you'd like to see it. You'll need to supply your own power supply, S-100 boards, and parts.

I am considering doing a small PCB manufacturing run in the relatively near future to assess this prototype. What I am looking for is a small group of experienced S-100 builders who'd like to purchase one of these boards (at cost, PCB only, plus shipping) to help with building it and checking it out. I am trying to keep the costs low but the PCB will be in the $30-$40 range.

If you are interested please contact me by PM or post here.

Thanks and have a nice day!

Andrew Lynch
 
Hi Mike, if you are willing to use wire wrap connectors and solder them in (heresy, I know) you can find them for $3 each on eBay. I've seen various prices around but from Digikey I recall the prices were like $7-$9 each for the proper connector with solder tabs.

I am specifying a 40 mil drill hole (0.04") for the S-100 connector. The PCB will be double thick for rigidity (1/8" or 3.2mm) and use double weight copper traces. The regular signal traces will be 17 mil width and power traces will be 51 mil width. The minimum clearance will be 11 mils. I will place copper pour fill zones for heat dissipation and grounding.

As soon as the trace router is done I'll post some PDFs of the schematic and PCB layout. The design is pretty neat as there are *no* vias other than the PTHs for devices.

Thanks and have a nice day!

Andrew Lynch

PS, not to discourage people but if you are considering this project you should be aware this is a "experimental untested prototype" release intended for hobbyists fairly experienced in electronics to help verify the design. It is *not* a kit and probably will contain errors requiring fixes before a general release. In other words, be prepared to use your own oscilloscope, VOM, soldering iron, S-100 boards, power supply, etc.
 
Hi! Based on some feedback I received on the N8VEM mailing list, I have totally redesigned the S-100 backplane. It is now a 6 slot unit with active termination. It includes mounting holes for each slot and additional chassis mounting holes for stress relief. Nearly all the traces have been migrated to the component side of the PCB and the copper side is almost entirely a ground plane for improved signal performance. There are no vias at all on the PCB and only the minimum PTHs for the components.

The PCB will be double thick for rigidity and durability (3.2mm or 0.125") and use double weight copper (2oz) for traces. Regular signal traces will be 17 mil wide and power traces will be triple width (51 mil) for low impedance rails. minimum clearance is 11 mils and normal round PTH pads used throughout. For now, the builder will have supply their own power supplies.

As soon as this unit completes its trace routing, I will update the files on the N8VEM wiki and request further comments. My plan is to make a small initial run of PCBs for advanced builders with two purposes in mind; find out if there are any major problems with the design and also to gauge the degree of interest in an amateur S-100 backplane.

Obviously, there are limits to making a prototype of this design so there is some degree of risk for the advance builders. The way to mitigate the risk is to do as much review as possible. I am making a good faith effort to make this as defect free as possible but as an amateur project there are no guarantees. Most likely any problems discovered can be resolved with the usual cuts and jumpers or other common work arounds.

Costs will be an issue with this project since the PCB is now about 7.5" on each side and over 50 square inches of area. That means the PCBs will be in the $30 to $40 range at the outset. Most of the components are common and relatively inexpensive but the S-100 connectors themselves are not easily obtained and can be expensive when you do find them.

Thanks and have a nice day!

Andrew Lynch
 
Hi! I updated the zip file with the information on the N8VEM wiki. If you have any comments or suggestions please I'd appreciate hearing them. I'd like to go to manufacturing soon with this design so if anyone is interested in participating in the trial run please let me know.

Thanks and have a nice day!

Andrew Lynch

PS, I swapped the copper and component planes so now almost all of the traces are on the copper side and the large copper pour/ground plane in on the component side.
 
Andrew,
I'd be really interested in buying one for my Mishmash computer. Let me know when you are getting ready to produce them. I will look over the plots again and let you know if I find anything dubious.

/Pontus
 
Andrew,
I'd be really interested in buying one for my Mishmash computer. Let me know when you are getting ready to produce them. I will look over the plots again and let you know if I find anything dubious.

/Pontus

Hi! Thanks! Yes, that is the ideal application for this S-100 backplane. My intent is for this to be a bench tool for home brew computing hobbyists to repair their S-100 boards and/or prototype new boards. It could be used to base a new home brew S-100 system but there is no case or chassis for it at the moment.

My recommendation is to test the backplane thoroughly before using it with boards. Also don't to use irreplaceable boards during the initial build until we're sure its working properly. You may consider using one of your S-100 prototype boards and rig a test board first.

If this backplane project is successful enough that it works and there is enough interest to at least cover my costs of its manufacturing run, I would like to take on some of the other difficult S-100 related hobbyist issues like the lack of readily available compatible linear power supplies, etc.

As you pointed out earlier, you can use SMPSUs but I've found them to be rather expensive solution ($100-$150 or so) since it appears, or at least I cannot find, a suitable SMPSU unit with three rails of 7.5 to 9 VDC, 15 to 18 VDC, and -18 to -15 VDC. That means multiple units are required and that gets expensive unless one wants to modify an SMPSU.

I investigated using a mixture of repurposed laptop and printer PS units but that is a nasty kludge and I don't think they have sufficient capacity for even a small S-100 system. As you said earlier, quality power supply is crucial to a reliable system. What would be a ideal would be a DC/DC converter to allow an ATX supply to be used but so far I've found nothing with useful current capacity with a reasonable price.

It'd be great if I was wrong but the really big problem with home brew S-100 systems is the power supply.

Thanks and have a nice day!

Andrew Lynch
 
Andrew,
How about implementing your own switched power supply on board the motherboard. There at least a million different good switched power supply controllers available from a number of vendors. This way a user could use one of the inexpensive notebook power supplies you mentioned earlier.

Pontus
 
Andrew,
How about implementing your own switched power supply on board the motherboard. There at least a million different good switched power supply controllers available from a number of vendors. This way a user could use one of the inexpensive notebook power supplies you mentioned earlier.

Pontus

Hi! I considered designing a custom SMPSU but to be honest I really don't have the experience to pull off one of those. While I am OK with designing a linear power supply as it is simple enough that I can probably get something to work "well enough." designing a SMPSU, at least a good one, is a really advanced skill.

My plan is to build the linear PS on a separate board and if it proves out possibly release a later design with an integrated backplane and linear power supply.

Thanks and have a nice day!

Andrew Lynch
 
I'm totally hooked on the LM2575. $2.45 at futurlec. Then you just need a few capacitors, a 1N5819 diode and a 330uH inductor that is under 1 ohm resistance. I got a whole pile of those for $2 each. I'm now dropping them onto boards instead of the 7805. They work exactly the same, except they only mildly get warm even when running at 800mA. When you factor in the cost of a heatsink for a 7805, the cost is about the same for a switcher. They run up to 1A.

You can have one for each voltage level. I don't know about the current levels - but an entire N8VEM with cmos components is only 65mA. But I guess if a board was LS (or TTL...). Or maybe seperate supplies for each board (if each one comes in under 1A). What are each of the rails driving? There are mods around to PC power supplies to tweak the output volts.
 

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Hi! The S-100 power supplies are really an odd mix and are probably almost unique in microcomputers. They are really comprised of two parts external and internal. The external power supply provides +8VDC, +18VDC, and -18VDC *unregulated* to the S-100 connector pins. Then the cards internal power supply section uses whatever local regulators it needs to create its rails as needed. That's why you see commonly see on S-100 boards 7805, 7812, 7905, 7912, zener diode circuits, and the like that you don't often see on more recent systems. It also makes building an S-100 power supply a real PITA.

With recent systems using supply voltages less than +3.3VDC I suppose you could say the two part power supply approach has made a come back. Many modern CPUs and memory systems use low voltages that the motherboard creates locally.

I am cobbling a temporary S-100 power supply together based on a mixture of low cost SMPSUs and repurposed laptop power supplies. It will probably work and not be too expensive but its no substitute for the real thing.

Thanks and have a nice day!

Andrew Lynch
 
Hi! I am expecting the first round of home brew S-100 backplanes to arrive in mid-May or so. They'll be available for $32 each plus shipping which is typically $2 in the US and $5 overseas. My intent is to get them to some S-100 enthusiast/hobbyists as low cost as possible while not taking a big loss myself. The $32 price is literally "at cost" -- the actual cost of the boards divided by the number of units.

These are prototype boards and only a small quantity will be available. The goal is to have these first generation boards get a thorough shake down to determine if they work well enough and there is sufficient interest to do a second generation.

Hopefully the initial round builders and testers can see this project as an investment and worthwhile. It is a prototype board so there is some risk involved. However, how many new S-100 backplanes can you buy anywhere these days at any price? Especially a low cost unit where you can influence the design. Vector was the last S-100 backplane manufacturer I know of. The IMSAI II team did release some units I think. I don't know if those actually made it out of testing though.

Thanks and have a nice day!

Andrew Lynch
 
Andrew,
I'm on for one. I have a few connectors left from my last order from Digikey which should be okey. By the way, what pitch between the connector rows are you using ?

/Pontus
 
Andrew,
I'm on for one. I have a few connectors left from my last order from Digikey which should be okey. By the way, what pitch between the connector rows are you using ?

/Pontus

Hi! I am using what I think are standard S-100 connectors. They are 0.125" (3.18mm) pitch connectors and 0.250" (6.36mm) between the two rows.

What part number did you order from Digikey so I can check the datasheet? Most S-100 backplanes that I know of use the 0.125"/0.250" combination. I suppose there could be variations as there are a *lot* of S-100 variants.

Thanks and have a nice day!

Andrew Lynch
 
Ouch, just checked my connectors and they are the Altair type who are 3.18mms between the rows. Anyway, you should go for the 0.125"/0.250" combo since those connectors are much less expensive than the Sullins connectors. I think mine were something like 16 bucks a piece and I had to get 20 of them. They have the 0.125"/0.250" on digikey at 8 bucks a piece and that's not too bad.

/Pontus
 
Hi! Thanks for the info on the S-100 connectors. I had assumed that since all of my S-100 related parts used the 0.125"/0.250" parts those were the way to go. I was not aware of the Altair parts until you pointed those out.

You are right though as the 0.250" parts are significantly less expensive. The good news is both S-100 connector styles seem to be in production and readily available. Not cheap but available. I see at Mouser you can get the parts for $5 each and I've seen even better deals on eBay.

Last night I received an email from the PCB manufacturer so I should be receiving the boards in the next few days. Also I ordered all the parts from Digikey so I can build a prototype. My 8VDC PS arrived but it requires some funky connectors :-( I may just solder to bypass them.

So this project is moving if glacially slow. More as it develops.

Thanks and have a nice day!

Andrew Lynch
 
Hi! I noticed a FedEx notice on my door yesterday when I got home so I think the S-100 backplanes will be delivered today unless its something else they are delivering. Also my package from Digikey arrived so I have most but not all of my parts now. Stand by for news!

Thanks and have a nice day!

Andrew Lynch
 
Hi! The S-100 backplane PCBs have arrived. Please contact me if interested getting one. Thanks and have a nice day!

Andrew Lynch
 
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