By John Ilsley. Over the next few issues, I intend to
cover some topics which I hope you will
find interesting. They range from
programming of simple routines, through
to making simple, yet amusing projects
for connection to the BBC.
I will be telling you how to connect an
infinite number of disc drives, 3" 3.5"
& 5.25" to one computer. They can even
be switched by the computer if you have
the software, which I am currently in
the process of writing.
I will explain to you how to adjust the
sound on your BBC A,B or Master for
just a few pence. I will be explaining
about Bulletin board systems, one of
which I run from 6pm till 12 midnight
Monday to Friday, and all day Saturday
and Sunday.
I have been working on the BBC computer
for only a short time really, a matter
of just six years, I started on the BBC
B with a single 40/80 track disc drive,
and a Taxan KP810 Epson compatible
printer. That was ok, but I found I
needed a bit more speed and a larger
capacity of both disc space and memory.
So I invested in a Master128 in October
1992, along with a 3.5" and a 5.25"
disc drive.
I have now expanded my system to cover
the above and two extra 5.25" drives,
a modem, over 150 roms, Eprom
programmer, Eprom eraser, Teletext
adaptor, Cassette unit, and a few more
things that are hanging around.
I can't program in machine code.
If you want any eprom chips programmed,
or even erased then give either Chris,
Daniel or myself a call for more
details.
If you have had previous issues of 8BS,
you will already have the worksheet for
the Master 128's switchable RAM/ROM
sockets and the BBC B's 6502 freeze.
Here's another to add to your
collection. This will allow you to add
a set of head phones to your BBC or
Master. Or adjust the volume so you can
play games late at night without waking
up the parents or the kids.
Before I continue, I must stress that
although I have these items in my own
machine, neither 8BS, the editors or
myself will accept any responsibility
should you misinterpret these
instructions, or if you make a hash of
it. Neither can we accept
responsibility should your model of BBC
be different for some reason. You
should only attempt this if you have a
working knowledge of electrics, and if
you are sure you can follow and
understand these instructions.
How to add an earphone socket and volume control to your computer.
You will need the following:-
(1). The computer that's a must!.
(2). A soldering iron and solder.
(3). About 3ft of wire, 22swg will
suffice, (Thats the thin stuff!).
(4). One 5k log variable resistor and
knob for the control.
(5). One mono/stereo socket.(Get the pin
out connections for this when you
buy it.
First turn off, and remove the power
supply. Then remove the top case. Do
this in the normal way. BBC B owners,
remove the 2 screws marked FIX at the
rear, and 2 underneath at the front
near the disc drive and Tube
connectors. Lift the top off.
Master128 owners remove any cartridges
you have in, then the four screws from
the base marked FIX, and lift the top
off.
Both need to have their keyboards
lifted forward, so just undo the screws
holding the keyboard in. The BBC B's
are on either side. The Master's are at
the bottom, below the space bar and one
near the PSU (PSU= Power Supply Unit),
and one last stupid one acting as some
silly earthing point for no real
reason, lift them forward a fraction.
This is what you will see:
BASIC
PSU
OTHER
FDC S ROMS
B
C
Q W E R T Y U I O P 7 8 9
4 5 6
A S D F G H J K L 1 2 3
0 . #
Z X C V B N M
POWER F
D
SUPPLY C
UNIT 6522
OS
A B
S
C
Q W E R T Y U I O P
A S D F G H J K L
Z X C V B N M
S=Speaker,
B=Speaker plug
C=Keyboard connector
On the BBC B, A=Volume control.
The two dots below the B are the leads
that lead from the mother board to the
speaker. One for each wire.
First I'll explain how BBC B owners can
turn the sound down with only a small
screwdriver. Follow the lead from the
speaker down until you come to an array
of resistors. You will see about 3cms
up and 4cms in from the PSU a tiny
square plastic box, about 1cm x .5cm in
size, it is likely to be either yellow
or blue. If you look at the rear of it,
you will notice a small circle with a
line in it, just large enough to take a
really small screwdriver. If you turn
it, it will increase or decrease the
volume.
Now, if you are really careful and
promise not to drop the metal
screwdriver you are using, I haven't
told you this, you should be able to
adjust the volume for yourself.
Type this first:
REPEAT:VDU7:UNTIL FALSE
then press RETURN. You will hear a
continuous beep. Carefully stick the
screwdriver into the slot in the
circle, making sure you don't let it
come into contact with anything other
than the adjuster, then turn it until
the required volume is achieved. Now
turn off, and remove the plug.
Adding a volume control and earphone
socket to the BBC B and Master128.
First, fix the volume control and
earphone socket into position.
On the BBC B, the rear of the computer
or the right hand side is a good place.
On the Master128, on the front is where
I have my stuff.
Now remove the speaker.
BBC B users, lift the keyboard and
remove the three screws fixing the
black case on, then take the speaker
out if you have one.
Master users lift out the battery
holder and pull at the back of the
plastic enough to lift the speaker out,
then feed it back through.
Desolder both wires from the speaker
and put them to one side.
Take the new wire and strip 2/3rds of a
cm off the end. Twist and flux it with
solder. Now solder that end to the
center pin of the 5k variable resistor.
Measure it along to where the speaker
would normally go. Make sure it won't
get trapped, then add another 2cm's to
it and cut it off. Twist and flux it,
now solder it to one of the wires you
removed from the speaker, the wire with
the plug on it. Stick a piece of
insulation tape around it so it doesn't
short out.
Now check you have that all done ok.
You should have one wire going from the
volume control to one of the speaker
wires.
Now, strip and flux another piece of
wire and solder it onto one of the
other pins on the 5k resistor. Take
that wire along to the earphone socket
and add another 2cm. Cut, Strip and
flux the end of that, then solder it to
earphone socket.
Where to solder the wire depends on
whether you have a mono (3pin) or
stereo (5pin) plug.
If you got the pin out from the
electronics shop, you want it to go to
the OUT. Don't worry if you do wire up
the socket incorrectly, it just means
more work.
Now take another piece of wire, twist,
flux and solder it to the earth of the
earphone socket. (Normally at the very
rear of the socket). Take this wire to
the place where the speaker is going to
be. Now cut it, strip 1 cm. Now take
another piece of wire and strip 1 cm
off the end of that, and twist both the
bare pieces of wire together. Solder to
the join the remaining wire from the
original plug you removed and wrap it
with insulation tape.
Take the other end of the wire to where
the speaker goes and add a little, then
cut, strip and flux the end. Solder it
to the connection on the speaker.
Now that was a little complicated, this
schematic drawing may help:
B
S
EARTH
P VR
H
S=Speaker.
PH=Headphone plug
VR=5k Log variable resistor
B=The plug from the mother board.
Take the remaining long piece of wire,
strip and flux the end, then solder it
to the other pin of the earphone
socket, the IN side. Measure it to
where the speaker is supposed to be.
Cut, strip and flux the end. Solder it
to the other terminal on the speaker.
Fix the speaker in, ensure that no bits
of solder have fallen on the computer
or the circuit board(s). Remove any
tools from inside.
BBC B users, if you have adjusted the
small volume control, ensure that it is
in an audible position.
Plug in the computer, but don't switch
on. Make some last final checks. Stick
in a pair of earphones and stick them
on your head, turn the new volume
control half way, and switch on the
computer.
If you don't get the normal startup
screen:
ACORN BASIC READY >
switch off and check everything
including solder on the chips and
track. If you get a normal screen,
type:
REPEAT:VDU7:UNTIL FALSE.
If you hear nothing, turn the volume
control first one way then the other.
You should then get something. If not,
remove the earphones, and turn the
volume control first one way then the
other. If you don't get sound then you
have the earphone socket wired badly.
If you get sound, but no volume
control, then you have wired the volume
control in badly.
If you don't get any sound, then you
have the earphone socket wired badly.
It is basically the earth and ac sound
wire connected together, switch off and
try the earphone wires in different
places.
The same goes for the volume control.
Any problems, contact me. If you phone,
expect a modem carrier.If you SHOUT
down the line, I will 99% of the time
hear you.
If it all went ok, turn off. Place the
wires neatly. Replace the keyboard and
outer case.
Now I hope your parents/kids don't wake
up while you're playing games.
Let me know what you think of this,
mainly the way it is explained and the
pictures.
John Ilsley 27N.