[Land-speed] OFF Topic: Trouble Shooting a Funky Breadboard circuit

[Larry Mayfield]

Ok, so I have made a bread board wiring system to replicate the wiring of a
1996 Ford Cruise Control system. It is a pretty simple system and is easy to
do, except....I have redone ti twice now because there are some oddities
going on.  This is only the wiring harness and the cruise control system is
not plugged in.  I did add one additional feature to the schematic, however.
It is a 17 dollar harbor freight tachometer. It has 4 hookup wires.  I have
a function generator and I checked it's operation before I put it into the
circuit. I set it to run based on 4 cylinder motor : ie it needs 2 pulses
per revolution to calculate the rpm. It does this admirably well. I can run
it from about 200 rpm right on up to full rpm or 8000 with no issues.  For
circuit try number one, I pu tit in and made a connection to the power in
the wiring. I used a small 9 - 18 volt adjustable, both voltage and current,
power supply and powered just the harness up.  Ok, so the harness worked
without issue. But since I want to run a cruise control servo with tis, I
decided I needed a larger power supply: I have 2 which are 13.8 volts
regulated and with short circuit protection. The only change I made was to
plug in power input banana jacks plugs from the small 12 volt supply to the
larger one. Hook up the scope and turned it on. Huh? Now the tach won't even
light up. Drove myself crazy trying to figure it out. Nothing I did lets the
tach work like it did with the small power supply. Oh, the small power
supply displays the amount of current going into the system when it is
hooked up, 0.08 amps.  No amp meter on the larger power supply however.  SO
I frustrated myself to no end before deciding that somehow there was s sneak
circuit in there somewhere.  I disassembled the circuit and rebuilt it with
fewer wires and lights. Wiring is much simpler now. Comes the moment of
truth... plug small power supply in, cross my fingers and power on. WORKS!
Just like it did before.  Now I power everything down, swap in the larger
power supply and Viola! It now does not even light up the tack let alone
make it work.  Well, crappa dooley... So I fiddle with the terminal board a
bit. Make sure that all screws are tight, etc. Still nothing...  Plug the
small power supply back it, all works.  Since I have two  of the big
supplies, I got the other one out of storage and removed it from its
original packing and box. Old, but unused.  Well, it now lights up the tach,
but the tack still does not work. Plug it back into the small power supply
and works.  I have now pulled most of the hair I have left on my head
out....

I need some pointers on what to maybe try next. I have a car battery on the
bench in a fully charged condition, I suppose I could try that. But what
particular areas of this might I be looking at. The circuit is wires,
resistors, momentary switches and toggle switches, and of course, the tach. 

Oh, why and I torturing myself this way? Well, I have this weird concept in
my head that I can use the cruise control, under desk top guidance to change
the rpm of a motor on my diy dyno.  I plan on using the function generator
to provide a speed signal to the  servo and I have buttons that I can
set/accelerate, coast, resume, and even a BOO switch to terminate it in an
upset event. Just like on the car schematic.  As soon as I can confirm a set
of parameters I can then hook up a relay board to jumper around the
momentary switches and let my process control software run the motor speed
up and down.  All the while applying dyno brake loading.  As stated, this
particular breadboard is just to find out some timing, and operational
characteristics of the servo unit itself. It is, by the way, a true servo.
It is however, not even hooked into this circuit yet because I cannot get
the tach to work to tell me the rpm I am testing the servo at, lol...

Since this is an OFF topic question, I would appreciate any and all of you
who wish to comment on this to do so directly to :   drmayf at mayfco.com.  No
use in clogging up the lists with stuff that only I am interested in...

Many thanks in advance!

mayf

_________________________
drmayf
Worlds Fastest Sunbeam, period.
204.913 mph flying mile
210.779 mph exit speed