Re: Oric Drives

Have just finished making up coiled lead between "Oric PC" and Keyboard.
Have also found some nice pre-ribboned 25 way d connectors i'll use for each
side.
I know you said 15 way, but i'm using what i have and what i can get away
with from work.
I have been thinking about the keyboard. Would it drain too much power from
the keyboard curcuit if i add an LED (with resistor) to the +5v connection?

This way i could tell when everything is connected.

I'm still not too keen on using the extra line for a reset button, i'd be
more inclined to use it as an audio line to a socket for headphones or for
the Cold Reset (I very rarely use soft-reset since i'm working in machine
code, and when a crash occurs, it really crashes! ;) ).

Twilighte

"Andre Majorel" <cheney@xxxxxxxxxxxxxxx> wrote in message
news:slrnde7riv.bt9.cheney@xxxxxxxxxxxxxxxxxxx
> On 2005-07-23, Twilighte <twilighte@xxxxxxxxxxxxxx> wrote:
>
>> That cable looks perfect Andre! And the price is not too bad, infact
>> i am willing to spend a little to get a decent Oric setup.
>>
>> Cool idea about the soft reset, since i don't have a spare button on
>> the front for it.
>>
>> About connector, i would hope to put a socket on the front of the pc
>> for the keyboard. Something like a 25 way D.
>
> I used something like RS 468-866 for the case (male) and RS
> 446-355 for the cable (female). Cheaper versions are available.
>
>> I found some nice angle brackets to mount the 3" drive in a 5.25" bay,
>> although do you know of any easier way to have a nice escution other
>> than cutting out one from a blank plastic plate?
>
> There are commercially available cradles (plate + brackets) for
> 3.5" but I've never seen any for 3".
>
>> The other problem i am a little concerned about is the ATX power
>> supply.
>> 1) Is their a good link to what all the connectors are?
>
> I think I posted a link to the ATX spec here a month or two ago.
>
>> 2) How do i know what sort of PSU it is?
>
> There are only three sorts on the market right now : AT, 20-pin
> ATX and 24-pin ATX. AT PSUs must be hard to find now.
>
>> 3) Are their any rules when taking power off them, such as are ATX
>> psu's switch-mode ones or balanced loading?
>
> As Jani said a few weeks ago, switching PSUs need a minimum load
> to regulate reliably. It seems that the higher the power rating
> of the PSU is, the higher the minimum current is so prefer a
> "small" PSU (200 W or less if you can find one).
>
> ARM users have reported problems with their ARM systems, which
> draw about 5 W. The Oric mainboard itself draws about 3 W. So,
> assuming the PSU needs 10 W, you'd have to sink another 7 W. You
> can do that with a resistor of R = U/I = U(P/U) = U²/P = 5²/7 =
> 3.57 ohms.
>
> For the 12 V line, assuming 10 W again, you'd need to sink 10 W.
> The resistor value would be R = U²/P = 12²/10 = 14.4 ohms.
>
> There are several choices of resistors. I think that the easiest
> would be to buy these two :
>
> RS 160-916 3.3R 50W £1.78
> RS 160-938 12R 50W £1.78
>
> Note that these are designed to be heat-sink mounted so screw
> them to the case of the PC. Position them on the outside and
> vertically so as not to hamper convection. Stagger them so that
> the top resistor is not in the hot air flow from the bottom
> resistor. Use thermal grease.
>
> Heat sinking is important. The data *** says that the
> resistors should be able to sink 20W on their own but they'll
> get dangerously hot. Even with the case acting as a (mediocre)
> heat sink, expect them to get as hot as 70°C. If that's too hot,
> I have enough aluminium scraps to make you a pair of heat sinks.
>
> Those resistors are big (30x73 mm). If space is a problem, the
> 25W version is shorter (RS 160-708 3.3R 25W £1.45) but I don't
> recommend it.
>
> As an alternative to resistors, Jani has suggested light bulbs.
>
>> 4) would the main oric board supply bypass the 9v curcuitry to
>> directly power the +5v?
>
> That's what I would do. I would remove the 7905 and connect the
> PSU there (0V to pin 1 of 7905, +5V to pin 3, pin 2
> unconnected). But please double check this with more competent
> people.
>
> --
> André Majorel <URL:http://www.teaser.fr/~amajorel/>
> (Counterfeit: wid@xxxxxxxxxxxxxxx rihohyc@xxxxxxxxx)
> "J'baiserai la France jusqu'à ce qu'elle m'aime." -- Un rappeur


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