able to turn it on and off while
driving to see tailgaters. My guess is
to put an on/off switch between the
reverse switch, but I have no
schematic. Can this be done?
— Walt Krol
AThe KIA shift lever is in the center console. Most likely the switch is connected to it and you will have to
remove the console cover; a repair
manual will be handy for doing that.
The switch is normally open, so all
you need to do is connect another
switch in parallel so it becomes an
There is no need to cut any
wires; you can get a splice at the
The splice is a plastic part with
metal inserts that cut the insulation
but not the wire. There is a channel
for the through wire and a short
channel for the splice. Place the
wires in the channels, fold the top
over, compress it with pliers, and
snap the retainer over the edge.
It is possible that the switch is
inside the transmission, but I doubt it.
The repair manual should tell you,
but in any case, the modification is
It is likely that the switch also
turns on the backup lights. In most
states, it is illegal to have white lights
at the rear of the vehicle while it is
going forward, so don’t drive around
with the backup lights on.
QI am a new subscriber to the magazine and am a beginner when it comes to electronics. I got the
magazine because I wanted to
practice reading schematics and
I read the book, Make:
Electronics by Charles Platt as an
introduction to electronics but I am
still struggling with schematics.
I wanted to try to understand
the simple cat alarm schematic
proposed in the August 2013 Q&A
I’m sure these questions are
really basic, so thank you for helping
22 October 2013
My LTspiceIV is a free simulation program that has
been enhanced for switching circuits (SPICE typically has a
problem with fast switching circuits; you’ll get a “time step
too small” error message).
The program has schematic capture and a waveform
viewer. You can download it from www.linear.com/
designtools/software. The manual is available in the
HELP file in the upper right corner.
There is an extensive library of Linear Technology
parts, but if you want to use some other device or a
transistor that is not in the library, you will have to find
the SPICE file and install it. To do that, use a search
engine (Google) and when the file is found, copy and
paste it into Notepad.
Now, go to C:\program files\LTC\LTspiceIV\lib\sub
and copy the file to that subdirectory if it is a subcircuit.
Now you need a symbol, so go back to \lib\sym and
double-click on the type of circuit, for example, an op-amp. The LT1012 is a typical op-amp with input, output,
and power pins that will fit many applications.
If you double-click on the symbol, it will open and you
can change the name. If you right-click on the red circle at
the name, a window opens that will allow you to change
the name. If you left-click, then you can choose delete.
If you delete, then use Draw/text to make a new name.
Save the symbol with a new name which must be the
same as the name of the subcircuit. You are not done yet.
The order of the pins in the symbol must be the
same as the order of pins in the subcircuit. For a five-pin
op-amp, the order is:
1. Positive input
2. Negative input
3. Positive power
4. Negative power
The actual numbers don’t matter; only the order is
important. If the order is different, edit the subcircuit.
LTspice will make the symbol for you. In the SPICE
file, right-click on the line that has the name of the
subcircuit and choose “Create Symbol” from the pop-up
If you have a transistor .model file, go to C:\program
files\LTC\LTspiceIV\lib\cmp and double-click on
standard.bjt. If it doesn’t open as a text file, open it with
Notepad. Just copy and paste the file and you are done.
If you want the library to display the manufacturer,
Vceo rating, and Ic rating, you can add that at the end of
the file; just use a space as a delimiter. The syntax is:
Vceo=xx icrating=xx mfg=yyy.
If there is not a subcircuit model available, you may
be able to make one using LTspice. Just draw the
schematic using simple parts. If it is too detailed, the
simulation may take a long time to run. Instead of a
transistor, use a current controlled current source; instead
of an op-amp, use a voltage controlled voltage source
because these will run much faster.
For example, I used an INA128 instrumentation
op-amp recently (I don’t know if a model is available;
I am going to make one as an exercise). The IC has three
op-amps and some resistors.
To start, I will simulate the over-voltage protection