Circuit Construction


Contents:
                             1.  Mod_1 Circuit
			     2.  Mod_2_(Easy) Circuit
			     3.  Circuit Testing




1.  Mod_1 Circuit:
=================

This is the same basic circuit as the VBS-BEST circuit.  Certain hard to
find elements have had there values changed to ones that are easier to
obtain. (IE 9K resistor -> 10K resistor)  Here is a complete parts list
of what you need to build this circuit.

Mod_1 Parts List
================

Capacitors:                  
   1 uF      (3)  
.001 uF      (1)

Resistors:    
  10K        (1)  These are all 5% 1/4 watt resistors....
   1K        (1)
 470 Ohm     (1)
 100 Ohm     (1)
  10 Ohm     (1)

Diodes:
 1N914       (2)

Transistors:
2N3906 (PNP) (1)

Operational-Amplifier:
LF-357 IC    (1)

Misc:
8 Pin IC Socket  (1)
Female RCA Jacks (2)
Female RS232 Connector
PC/IC mounting board



2. Mod_2_(EASY) Circuit:
=======================

This is a modified VBS-BEST circuit.  Certain hard to find elements have
had there values changed to ones that are easier to obtain.  (IE 9K
resistor -> 10K resistor).  The Composite Video Output section of the
circuit been deleted along with a simplification of the capacitors on
the voltage source nodes.  I use this circuit on my computer and have
had no problems with reliability or function.  This circuit is a bit easier
to build and I simply use the tape counter instead of the monitor to 
position the VCR Tape.  Here is a complete parts list of what you need to
build this circuit.

Mod_2_(Easy) Parts List
=======================

Capacitors:                  
.001 uF      (1)
   1 uF      (2)  Note:  The value of the Cap' used between +12 and -12
                  is very flexible.  I used a .68 micro-Farad, 50 volt
		  cap I had on hand.  Any value from about .5uF to the
                  original 4.7F should work well.  .1uF to 10uF are maybes,
		  if anyone builds one and it works let me know.
		  Make sure that the Cap' can handle the voltage (24
		  Volts).

Resistors:    
  10K        (1)  These are all 5% 1/4 watt resistors....
   1K        (1)
 100 Ohm     (1)

Diodes:
 1N914       (2)

Operational-Amplifier:
LF-357 IC    (1)

Misc:
8 Pin IC Socket  (1)
Female RCA Jacks (1)
Female RS232 Connector
PC/IC mounting board


In constructing this circuit I used a female right-angle RS232 connector
and a small 1 3/4 X 1 3/4 IC mounting board to keep this thing small.
Using a pair of small wire cutters (finger-nail clippers work well!) I
nipped off all the pins from the RS232 except PINS 3, 7, 9, and 10.  Be
very careful if you do this as a mistake here will cost you a new
connector....  I then soldered the IC mounting board directly to the
modified connector and wired the circuit appropriately (See
Mod2_Layout.IFF).  With all circuit components in place I soldered an RCA
female jack directly onto the board and secured the connector, board and
jack together with a small amount of CA adhesive and hot-glue.  One day I
may put it in a case, but I'm in no hurry, the entire assembly is very
small and quite strong.

If you choose to build this circuit make sure you are accurate in all of
your connections.  Solder neatly and double check everything!  If you have
an ohm meter and or a logic-probe test this circuit before you connect it
to your computer.




3. Circuit testing:
==================

In order to safely test any of these circuits you should have a logic probe
and/or multi-meter.

Step 1:  Connect your Amiga Composite to the Video In jack of your VCR.
         (Make sure your VCR is on the right channel, [ 0, 99, AUX...])

Step 2:  Change the VBS tooltype VIDEOCHECK=ON to VIDEOCHECK=OFF.  This
         will allow you to record a VBS backup w/ the circuit in place.

Step 3:  Create a small VBS backup (read the directions for VBS).

Step 4:  Using two 9 volt batteries in series, power the circuit up. 

         + (9) - + (9) -     <--- 9 Volt Batteries

         ^      ^      ^
Pin #    9      7      10

	Using a multi-meter, check the current flowing thru the circuit.
        It should be about 5mA or less....  If you have much more than 5mA
        flowing double check your layout to make sure you haven't shorted
        something.  If you don't have a multi-meter feel each circuit
        element with your fingers.  If anything is WARM or HOT disconnect
        the circuit power and look for mistakes.

Step 5: Connect the Video-Out of your VCR to the RCA jack on the circuit.
        Rewind the tape and playback the backup you just recorded.  While
        the tape is playing examine pin 3 of the RS232 connector or pin 6
        of the Op-Amp IC with the logic-probe.  You should see an
        oscillating signal (Hi<>Low)....  If you don't see this double
        check your circuit for a mistake somewhere.  

	NOTE:  If you don't find the (HI<>LOW) signal at pin 6 (IC) check
	your Video-In connector w/ the logic probe.  If you don't see any
	signal there you either don't have anything coming from the VCR or
	you have really wired something wrong.



If your circuit has passed these tests it should be safe to connect it 
to your computer.  Don't forget to change the VBS tooltype back to
 VIDEOCHECK=ON.  This will make sure your circuit is operating properly
every time you do a backup.

Remember to check your connections.  I take no responsibility as to the
accuracy or function of these circuits or any damage caused by there use.
 	 

If anyone has questions or comments on these circuits I can be reached at
FIDO 1:151/115.0

Ken Isley