Briel replica-1 and ACI solution without -12v

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Joined: Oct 9 2011
Posts: 1046

So I keep forgetting to post this....

Anyway, if you are using a wallwart or usb for power on your replica-1 and would like to use Mike Willegal's ACI or similar one the power supply on the Briel for some reason isn't consistent enough to use Mike Willegal's trick of -12V to ground. I have tried it with both Mike's exact replica and Vince's "beta" ACI. Both seem to work in an Apple-1 semi ok with -12v to ground, though you need a little more volume to read cassettes.

My first trick to avoid a big power supply with -12V was to use the onboard MAX232 as a voltage pump. This yielded about -3 volts. Enough to make it work much much better, but the moment you hooked up anything on the replica-1 serial it was toast. So I simply added an extra chip, the Max 202 with a couple of .1 caps (just like the sample in the datasheet) to the proto area and routed my -12 from the expansion port (pin Z) from the Max202's pin #6. With this change I can now load from cassette, iPod with as much reliability as the ACI on an Apple-1, which isn't perfect but pretty darn good for 1976.

Now my replica-1 is also a little more tricked out, in that I added a 39D 5300uf cap to the power supply because my radioshack wallwart was a little noisy and I happened to have one with a 1990's date code that I didn't care about. You don't have to use a $25 cap for that, simply use a modern one that only cost a couple of cents with a similar value.

One more note: if you have an EEPROM and not an eprom, there may be too much noise on the bus as well. You can simply swap out your EEPROM with a compatible eprom programmed with the code. If you have a problem with doing that PM me, I may be able to help as I have a programmer. Vince may also be able to help.

Anyway just thought I should let others know since I think loading off an ACI, even with an iPod, is much more fun than using something like a CFFA card setup.


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Joined: Jun 5 2008
Posts: 380
Re: Briel replica-1 and ACI solution without -12v

Hi Corey,

I expect you probably used what you had on hand, but if I was going to generate a negative supply specifically for the voltage comparator on the ACI, I would first try using a 7660 voltage converter IC or similar. The 7660 is only 8 pins and requires just a couple of capacitors to do it's job. Example schematics for basic voltage inverters are in the data sheets.

Mike Willegal