A500 trapdoor memory: free design

[katarakt]

Really? How stupid is that? Ok..we have the chance patzik will do it right, i hope so

[majinga]

Why? The led is almost useless here. Once the case is closed, the led is no longer visible.
To check what is enabled and what is not, check the jumpers.

[Chain]

how about translucent cases, which are on its way, somehow

[majinga]

Even in this case the led can still always on.
The led is to indicate if the board is powered or not. It has nothing to do with settings.

[Chain]

ah thats not good, led should lit when board is enabled

[majinga]

What do you mean with enabled? Ram or RTC?

And why should someone keep a disabled board inside his A500?

[patzik]

Ok, I did the last corrections and added the led jumper next to the select switch jumper. They share a common ground so only 3 wires needed.
The resistor is the same resistor as used with the onboard led, so if you need to make the led less or more bright, R6 is the resistor you need to change.
This led is just as the onboard led, and always lights up, unless you use a 4 pole switch (spdt), in that case you would switch the led and the expansion on/off at the same time.

[majinga]

Ah, so, that's the purpose of the switch on the bottom right corner. I wondered what it was for.

Just a suggestion, maybe it is better to add a silk-screen to indicate how to use the jumper.

[katarakt]

Great !! Thanks a lot!

But you haven't done all i think:

C20 change from 2.5mm to 2mm RM done ?

You have to line up the 3pin sw/led with the sel 0 sel 1 2pin gary header...so, move the 2pin a little bit more to the right of the board so the vh connector can be turned 180 degrees. Check my picture, you can see what i mean. Tomorrow i can modify the picture and measure the board...don,t know if i can describe it enough with words.

Yes ...silkscreen hint is missing for led function.

Final version silkscreen should be Rev B.7

About using a LED. With final version someday i'll use this ramexpansion with a switch i'm going to put on the back right behind the floppy. This switch has an LED built-in ...now guess...i turn on the ramexpanion and LED shows that ramexpansion is turned on

But, now we have every combination and everyone can choose which led setting he want

Btw...does anybody know for what the 2 big holes are ??? Maybe they should be deleted too ?

[mc6809e]

Back in the day I used the piggy-back method to bring my A500 to 1Meg.

I can't remember the details but basically I soldered another 16 chips on top of the 16 already on the motherboard, making sure not to solder the RAS lines. Those I pulled up to be horizontal and soldered all of them to wires that went to the appropriate RAS select on the motherboard. I might also have had to break a trace on the motherboard but I can't remember.

Of course there was no real time clock but it didn't matter at the time.

I think I got the 512K of memory from an old 68K workstation that a friend had.

And it was all free!

At one time I also wound up using an Atari ST color monitor. I had been using an old monochrome monitor (no joke) and a friend had gave me (for free again) an ST color monitor. It was easy to get it to work with the Amiga. Looked really good, too!

I remember thinking how much better it looked than the Commodore Amiga monitors!

[majinga]

Originally Posted by katarakt

...

Btw...does anybody know for what the 2 big holes are ??? Maybe they should be deleted too ?

I don't know what they are for.

But this start to be a big and heavy expansion board, if full populated. The A500 connector can't take it all the way up alone. The external hole can be used with a pcb stand-off, to keep the board up when the trapdoor is closed. Not easy to select the right stand-off, but, still an option.




Or maybe a pcb feet, mounted on the top side. Used as guide with the trapdoor rail.

Anyway, in my opinion, keep them, they can be useful in a way or another.

[majinga]

Or better, they can be turned into a big vias, to keep the ground planes perfectly connected.
In this way they also can be used for stand-offs, pcb-foots, an other things like that.

[Mathesar]

Originally Posted by katarakt

Really? How stupid is that? Ok..we have the chance patzik will do it right, i hope so

It is a power led! And good stuff has to have a nice shiny power led

[PeteAU]

Originally Posted by patzik

Ok, I did the last corrections and added the led jumper next to the select switch jumper. They share a common ground so only 3 wires needed.
The resistor is the same resistor as used with the onboard led, so if you need to make the led less or more bright, R6 is the resistor you need to change.
This led is just as the onboard led, and always lights up, unless you use a 4 pole switch (spdt), in that case you would switch the led and the expansion on/off at the same time.

Would the cheap board houses actually fabricate that? I would have doubts, but show us a photo if they do.

Originally Posted by Mathesar

It is a power led! And good stuff has to have a nice shiny power led

It also needs to be blue to be cool.

[demolition]

Originally Posted by PeteAU

It also needs to be blue to be cool.

And pulsating so it can really attract attention.

[CRP]

Hi, does anybody know if this expansion is compatible with a TF530 in an A500 rev 6A?

Thanks

[mamejay]

Hi everyone. This could be a silly question. I wanted to make just a basic 512k version of this to expand stock A500's to use. This was to be a very slim memory board.
I based my works on the B6 schematic and just ripped out everything except for the DRAM and a capacitor. In my haste I missed wiring the enable pin to gnd and also the RAS pin (Pin 14) on the DRAM to the expansion port.
I fixed these using some hookup wire but I still cannot get my Amiga's to detect memory.
I revisited the B6 schematic and compared with my board and found one additional thing which I have not had a chance to check. A9 (Pin 28) of the DRAM is left floating on my board and should be tied to GND.
Would this stop the board from working or am I missing something else?
Last thing I only allowed for 1 decoupling cap 100nf as this is what I saw on the first couple of threads that was needed. Now reading more looking like Pete is stating to use at least 2.
As stated this is a very very very basic 512k board. I will get around to testing but thought someone here may have the answer.

thanks

[SukkoPera]

Originally Posted by CRP

Hi, does anybody know if this expansion is compatible with a TF530 in an A500 rev 6A?

I think so. I'm using it with a HC533 and it works well.

Also I am using it in the A500+ configuration on another machine with a TF530 and it works well, too.

[alenppc]

Originally Posted by CRP

Hi, does anybody know if this expansion is compatible with a TF530 in an A500 rev 6A?

Thanks

Certain TF530 firmware revisions (RC 1/2) don’t work with 1.5 mb slow-fast, so you have to limit it to 1mb but otherwise it works fine.

[CRP]

Originally Posted by alenppc

Certain TF530 firmware revisions (RC 1/2) don’t work with 1.5 mb slow-fast, so you have to limit it to 1mb but otherwise it works fine.

I have a rev 3, so I will try it.

Thanks!