By John Ilsley. Over the next few issues, I intend to cover some topics which I hope you willfind interesting. They range from programming of simple routines, throughto making simple, yet amusing projects for connection to the BBC. I will be telling you how to connect aninfinite number of disc drives, 3" 3.5"& 5.25" to one computer. They can even be switched by the computer if you havethe software, which I am currently in the process of writing. I will explain to you how to adjust thesound 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 computerfor only a short time really, a matter of just six years, I started on the BBCB 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 October1992, 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 forthe 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 canplay games late at night without wakingup 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 ofit. Neither can we accept responsibility should your model of BBCbe 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 willsuffice, (Thats the thin stuff!).
(4). One 5k log variable resistor andknob for the control.
(5). One mono/stereo socket.(Get the pinout connections for this when youbuy 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 screwsholding the keyboard in. The BBC B's are on either side. The Master's are atthe bottom, below the space bar and onenear 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:
FDC S ROMS
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
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 canturn the sound down with only a small screwdriver. Follow the lead from the speaker down until you come to an arrayof resistors. You will see about 3cms up and 4cms in from the PSU a tiny square plastic box, about 1cm x .5cm insize, 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 areally 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 whereI 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 acm 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 withthe plug on it. Stick a piece of insulation tape around it so it doesn'tshort out. Now check you have that all done ok. You should have one wire going from thevolume 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 toearphone 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 tobe. Now cut it, strip 1 cm. Now take another piece of wire and strip 1 cm off the end of that, and twist both thebare pieces of wire together. Solder tothe join the remaining wire from the original plug you removed and wrap it with insulation tape. Take the other end of the wire to wherethe speaker goes and add a little, thencut, strip and flux the end. Solder it to the connection on the speaker. Now that was a little complicated, thisschematic drawing may help: B
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 bitsof 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 isin 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 volumecontrol 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 andtry 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 wakeup 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.