APPENDIX B : BASICS OF WIRE WRAPPING

1. 
   
   Wire-wrapping wire is available prestripped in various lengths or in bulk on a
   spool. The prestripped wire is usually more expensive and you are restricted to
   the different wire lengths you can afford to buy. Bulk wire can be cut to any
   length you wish, which allows each wire to be custom fit.
   
2. 
   
   Serveral different types of wire-wrap boards are available. These are usually
   called perfboards or wire-wrap boards. These types of boards are sold at many
   electronics stores (such as Radio Shack). The best type of board has plating
   around the holes on the bottom of the board. These boards are better because
   the sockets and pins can be soldered to the board, which makes the circuit more
   mechanically stable.
   
3. 
   
   Choose a board that is large enough to accommodate all the parts in your
   design with room to spare so that the wiring does not become too cluttered. If
   you wish to expand your project in the future, you should be sure to include
   enough room on the original board for the complete circuit. Also, if possible,
   the layout of the 1C on the board needs be done such that signals go from left
   to right just like the schematics.
   
4. 
   
   To make the wiring easier and to keep pressure off the pins, install one stand
   off on each corner of the board. You may also wish to put standoffs on the top
   of the board to add stability when the board is on its back.
   
5. 
   
   For power hook-up, use some type of standard binding post. Solder a few sin
   gle wire-wrap pins to each power post to make circuit connections (to at least
   one pin for each 1C in the circuit).
   
6. 
   
   To further reduce problems with power, each 1C must have its own connection
   to the main power of the board. If your perfboard does not have built-in power
   buses, run a separate power and ground wire from each 1C to the main power.
   In other words, DO NOT daisy chain (chip-to-chip connection is called daisy
   chain) power connections, as each connection down the line will have more
   wire and more resistance to get power through. However, daisy chaining is
   acceptable for other connections such as data, address, and control buses.
   
7. 
   
   You must use wire-wrap sockets. These sockets have long square pins whose
   edges will cut into the wire as it is wrapped around the pin.
   

9. Wire wrapping will not work on round legs. If you need to wrap to components, such as capacitors, that have round legs, you must also solder these connections. The best way to connect single components is to install individual wire-wrap pins into the board and then solder the components to the pins. An alternate method is to use an empty 1C socket to hold small components such as resistors and wrap them to the socket.

1. 
   
   The wire should be stripped about 1 inch. This will allow 7 to 10 turns for each
   connection. The first turn or turn-and-a-half should be insulated. This prevents
   stripped wire from coming in contact with other pins. This can be accom
   plished by inserting the wire as far as it will go into the tool before making the
   connection.
   
2. 
   
   Try to keep wire lengths to a minimum. This prevents the circuit from looking
   like a bird nest. Be neat and use color coding as much as possible. Use only
   red wires for V_cc and black wires for ground connections. Also use different
   colors for data, address, and control signal connections. These suggestions will
   make troubleshooting much easier.
   
3. 
   
   It is standard practice to connect all power lines first and check them for con
   tinuity. This will eliminate trouble later on.
   
4. 
   
   It’s also a good idea to mark the pin orientation on the bottom of the board.
   Plastic templates are available with pin numbers preprinted on them specifi
   cally for this purpose or you can make your own from paper. Forgetting to
   reverse pin order when looking at the bottom of the board is a very common
   mistake when wire wrapping circuits.
   
5. 
   
   To prevent damage to your circuit, place a diode (such as IN5338) in reverse
   bias across the power supply. If the power gets hooked up backwards, the
   diode will be forward biased and will act as a short, keeping the reversed volt
   age from your circuit.
   
6. 
   
   In digital circuits, there can be a problem with current demand on the power
   supply. To filter the noise on the power supply, a 100 fiF electrolytic capacitor
   and a 0.1 |jF monolithic capacitor are connected from V_cc to ground, in par
   allel with each other, at the entry point of the power supply to the board. These
   two together will filter both the high- and the low-frequency noises. Instead of
   using two capacitors in parallel, you can use a single 20-100 ixF tantalum
   capacitor. Remember that the long lead is the positive one.
   
7. 
   
   To filter the transient current, use a 0.1 uF monolithic capacitor for each IC.
   Place the 0.1 uF monolithic capacitor between Vcc and ground of each IC.